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A  COMPLETE  TREATISE 


ON    THE 


ELECTRO-DEPOSITION  OF  METALS! 

COMPRISING 

ELECTRO-PLATING    AND    GALVANOPLASTIC    OPERATIONS,    THE    DEPOSITION    OF 

METALS  BY  THE  CONTACT  AND  IMMERSION  PROCESSES,  THE  COLORING  OF 

METALS,  LACQUERING,  THE  METHODS  OF  GRINDING  AND  POLISHING, 

AS   WELL  AS 

DESCRIPTIONS  OF  THE  VOLTAIC  CELLS,  DYNAMO-ELECTRIC  MACHINES, 

THERMO-PILES.  AND  OF  THE  MATERIALS  AND  PROCESSES 

USED  IN  EVERY  DEPARTMENT  OF  THE  ART. 

TRANSLATED  FROM  THE  LATEST  GERMAN  EDITION  OF 

DR.  GEORGE  LANGBEIN, 

PROPRIETOR    OF   A    MANUFACTORY    FOR    CHEMICAL   PRODUCTS,    MACHINHS,    APPARATUS, 

AND    UTENSILS   FOR    ELECTKO-PLATBRS   AND    OF   AN   ELECTRO-PLATING 

ESTABLISHMENT    IN    LEIPZIG.jj 

WITH  ADDITIONS  BY 

WILLIAM  T.  BRANNT, 

EDITOR    OF  THE   "  TECHNO-CHEMICAL    RECEIPT   BOOK/' 

SEVENTH  EDITION,  REVISED  AND  ENLARGED. 
ILLUSTRATED  BY  ONE   HUNDRED   AND  FIFTY-FIVE  ENGRAVINGS. 


PHILADELPHIA  : 
HENRY  CAREY  BAIRD  &  CO., 

INDUSTRIAL  PUBLISHERS,  BOOKSELLERS,  AND  IMPORTERS, 

810  WALNUT  STREET. 

1913 


COPYRIGHT,  BY 

HENEY  CAKEY  BAIKD  &  CO. 
1913. 


PRINTED   AT  THE 

WlCKERSHAM    PRINTING    HOUSE, 

111-117  EAST  CHESTNUT  STREET, 

LANCASTER,  PA..  U.  8.  A. 


PREFACE  TO  THE  SEVENTH  AMERICAN  EDITION. 


THE  number  of  American  editions  through  which  Dr.  George 
Langbein's  work,  Handbuch  der  elecktrolytischen  Metall-Nieder- 
•schlage,  has  passed  in  rapid  succession,  and  the  continued 
demand  for  it,  may  be  accepted  as  evidence  that  the  book, 
written  from  a  scientific,  as  well  as  practical,  standpoint,  has 
been  found  to  fulfill  the  purpose  for  which  it  is  primarily 
intended,  namely  to  serve  as  a  ready  book  of  reference  and 
practical  guide  to  the  electroplater,  who,  if  he  would  be  a 
master  of  his  art,  must  be  conversant  with  the  scientific  prin- 
ciples upon  which  it  rests. 

In  this  the  seventh  American  edition,  now  presented  to  the 
public,  the  general  scheme  and  scope  of  the  sixth  edition  have 
been  retained,  but  a  thorough  revision  has  been  made,  and  a 
good  deal  of  new  matter  has  been  added. 

Due  attention  has  been  paid  to  all  important  innovations, 
and  it  has  been  endeavored  to  include  all  practical  methods 
of  plating  which  have  become  known  since  the  publication  of 
the  sixth  edition,  as  well  as  the  most  recent  machinery  and 
apparatus. 

The  editor  is  under  obligations  to  The  Hanson  &  Van 
Winkle  Co.,  ot  Newark,  iJ.  J.,  the  well-known  manufacturers 
of,  and  dealers  in,  electroplaters'  supplies  and  to  The  Egyptian 
Lacquer  Manufacturing  Co.,  of  New  York,  for  valuable  in- 
formation and  engravings.  He  has  also  diligently  consulted 
the  leading  trade  journals  and  freely  quoted  from  them,  due 
credit  having  been  given  in  the  text ;  but  he  would  acknowl- 
edge his  special  indebtedness  to  "  The  Metal  Industry." 

The  publishers  have  spared   no  expense  in  the  proper  il- 


355432 


IV  PREFACE    TO    THE    SEVENTH    AMERICAN    EDITION. 

lustration  and  the  mechanical  production  of  the  work,  and, 
like  the  previous  editions,  it  has  been  provided  with  such  a 
copious  table  of  contents  and  very  full  index  as  to  render 
reference  to  any  subject  prompt  and  easy. 

W.  T.  B. 

PHILADELPHIA,  OCTOBER  15,  1913. 


PREFACE  TO  THE  FIRST  AMERICAN  EDITION. 


THE  art  of  the  electro-deposition  of  metals  has  during  recent 
years  attained  such  a  high  degree  of  development  that  it  was 
felt  that  a  comprehensive  and  complete  treatise  was  needed  to 
represent  the  present  advanced  state  of  this  important  industry. 
In  furtherance  of  this  object,  a  translation  of  Dr.  George  Lang- 
bein's  work,  Vollstdndiges  Handbuch  der  Galvanischen  Mettall- 
Niederschldge,  is  presented  to  the  English-reading  public  with 
the  full  confidence  that  it  will  not  only  fill  a  useful  place  in 
technical  literature,  but  will  also  prove  a  ready  book  of  refer- 
ence and  a  practical  guide  for  the  workshop.  In  fact,  it  is 
especially  intended  for  the  practical  workman,  wherein  he  can 
find  advice  and  information  regarding  the  treatment  of  the 
objects  while  in  the  bath,  as  well  as  before  and  after  electro- 
plating. The  author,  Dr.  George  Langbein,  is  himself  a 
master  of  the  art,  being  the  proprietor  of  an  extensive  electro- 
plating establishment  combined  with  a  manufactory  of  chem- 
ical products,  machinery  and  apparatus  used  in  the  industry. 

The  results  yielded  by  the  modern  dynamo-electric  ma- 
chines, to  which  the  great  advance  in  the  electro-plating  art  it 
largely  due,  are  in  every  respect  satisfactory,  and  the  more  so 
since  the  need  of  accurate,  and  at  the  same  time  handy, 
measuring  instruments  has  also  been  supplied.  With  the 
assistance  of  such  measuring  instruments,  the  establishment 
of  fixed  rules  regarding  the  current-conditions  for  an  electro- 
plating bath  has  become  possible,  so  that  good  results  are 
guaranteed  from  the  start.  While  formerly  the  electro-plater 
had  to  determine  the  proper  current-strength  for  the  depositions 
in  an  empirical  manner,  by  time-consuming  experiments,  to- 
day, by  duly  observing  the  determined  conditions,  and  pro- 

(v) 


VI  PREFACE    TO    THE    FIRST    AMERICAN    EDITION.  ' 

vided  with  well-working  measuring  instruments,  he  can  at  once- 
produce  beautiful  and  suitable  deposits  of  the  various  metals. 

The  data  referring  to  these  current-conditions,  according  to 
measurements  by  Dr.  Langbein,  are  given  as  completely  as 
possible,  while  for  the  various  baths,  only  formulae  yielding 
entirely  reliable  results  have  been  selected.  To  most  of  the 
baths  a  brief  review  of  their  mode  of  action  and  of  their  ad- 
vantages for  certain  uses  is  added,  thus  enabling  the  operator 
to  select  the  bath  most  suitable  for  his  special  purpose.  To 
the  few  formulae  which  have  not  been  tested,  a  note  to  that 
effect  is  in  each  case  appended,  and  they  are  only  given  with 
due  reserve. 

To  render  the  work  as  useful  as  possible,  the  most  suitable 
formula  for  plating  by  contact  and  immersion,  as  well  as  the 
best  methods  for  coloring  the  metals,  and  the  characteristic 
properties  of  the  chemicals  used  in  the  industry,  are  given. 
However,  the  preparation  of  the  chemicals  has  been  omitted, 
since  they  can  be  procured  at  much  less  expense  from  chemi- 
cal works  than  it  would  be  possible  for  the  electro-plater  to 
make  them  in  small  quantities,  even  if  he  possessed  the  neces- 
sary apparatus  and  the  required  knowledge  of  chemistry  and 
skill  in  experimenting. 

It  is  hoped  that  the  additions  made  here  and  there  by  the 
translator,  as  well  as  the  chapter  on  "  Apparatus  and  Instru- 
ments," and  that  on  "  Useful  Tables."  added  by  him,  may 
contribute  to  the  usefulness  of  the  treatise. 

Finally,  it  remains  only  to  be  stated  that  the  publishers 
have  spared  no  expense  in  the  proper  illustration  and  the 
mechanical  production  of  the  book  ;  and.  as  is  their  universal 
practice,  have  caused  it  to  be  provided  with  a  copious  table  of 
contents,  and  a  very  full  index,  which  will  add  additional 
value  by  rendering  any  subject  in  it  easy  and  prompt  of 
reference. 

W.  T.  B. 

PHILADELPHIA,  JULY  1,  1891. 


CONTENTS. 


I. 
HISTORICAL  PART. 


CHAPTER  I. 
HISTORICAL  REVIEW  OF  ELECTRO-METALLURGY. 

PAGE 

The  method  of  coating  metals  by  simple  immersion  known  to  Zozimus 
and  Paracelsus;  Luigi  Galvani's  discovery,  in  1789,  of  the  electric 
contact-current;  Alexander  Volta's  discovery,  in  1799,  of  the  true 
causes  of  the  electric  contact-current;  Galvani's  experiments  •  .  i 

Erroneous  inference  drawn  by  Galvani  from  his  experiments;  General 
ignorance  in  regard  to  the  electric  current;  Discovery  which  led  to 
the  construction  of  the  pile  of  Volta,  or  the  voltaic  pile;  Cruik- 
shank's  trough  battery 2 

Decomposition  of  water  by  electrolysis  by  Nicholson  and  Carlyle, 
1800;  Wollaston's  observations,  1801;  Cruikshank's  investigations, 
1803;  Brugnatelli's  experiments  in  electro-gilding,  1805;  Sir  Hum- 
phry Davy's  discovery  of  the  metals  potassium  and  sodium,  1807; 
Prof.  Oersted's  discovery  of  the  deflection  of  the  magnetic  needle, 
1820 3 

Construction  of  the  galvanoscope  or  galvanometer;  Ohm's  discovery, 
in  1827,  of  the  law  named  after  him;  Faraday's  discovery,  in  1831, 
of  electric  induction;  First  electro-magnetic  induction  machine  con- 
structed byPixii;  Faraday's  electrolytic  law  laid  down  and  proved  in 
1833;  Production  of  iridescent  colors,  in  1826,  by  Novili;  Production 
of  the  amalgams  of  potassium  and  sodium,  in  1853  by  Bird  .  .  4 

Discovery  of  the  actual  galvanoplastic  process,  in  1838,  by  Prof. 
Jacobi;  Claims  of  priority  of  invention  by  T.  Spencer,  and  C.  J.  Jor- 
dan; Labors  of  the  Elkingtons  and  of  De  Ruolz;  Murray's  discov- 
ery, in  1840,  of  black-leading 5 

Introduction,  in  1843,  of  gutta-percha  by  Dr.  Montgomery;  First  em- 
ployment, in  1840,  of  alkaline  cyanides  by  Wright;  Patent  for  the 
deposition  of  nickel,  1840;  Origination  of  the  term  "electro-metal- 
lurgy" by  Mr.  Alfred  Smee,  1841;  Prof.  Bcettger's  discovery,  in 
1842,  of  the  deposition  of  nickel  from  its  double  salt  ....  6 

(vii) 


Vlll  CONTENTS. 


First  deposition  of  metallic  alloys  by  De  Ruolz;  First  use  of  thermo- 
electricity, in  1843,  by  Moses  Poole;  Advances  in  the  art  of  electro- 
deposition;  First  magnetic  machine  that  deposited  silver  on  a  prac- 
tical scale  constructed,  in  1844,  by  Woolwych;  Attempts,  since  1854, 
by  Christoffle  and  Co.,  to  replace  their  batteries  by  magneto-elec- 
trical machines;  The  Alliance  machine;  Objections  to  Wilde's 
machine;  Dr.  Antonio  Pacinotti's  invention,  in  1860,  of  the  ring 
named  after  him.  

Siemens'  dynamo  machine,  1866;  Wheatstone's  dynamo  machine, 
1867;  Zenobe  Gramme's  machine,  1871;  Hefner- Alteneck's  machine, 
1872;  Siemens  &  Halske  machine,  1874;  S.  Schuckert's  machine; 
Impetus  given  to  the  electro-plating  industry  by  the  construction  of 
suitable  dynamo  machines 


II. 

THEORETICAL  PART. 


CHAPTER  II. 
MAGNETISM  AND  ELECTRICITY. 

Magnetism. 

Loadstone  or  magnetic  iron  ore;  Natural  and  artificial  magnets    .         .      9 
Definition  of  the  magnetic  poles;  Neutral  line  or  neutral  zone;  Mag- 
netic meridian;  North  and  south  poles;  Phenomena  of  attraction  and 

repulsion;  Ampere's  theory 10 

Magnetic  field n 

Electro-Magnetism . 

Direction  of  the  reflection  of  a  magnetic  needle;  Instruments  for  recog- 
nizing feeble  currents .11 

Galvanoscopes  or  galvanometers;  Astatic  galvanometer;  Instruments 
for  measuring  the  intensity  of  the  current  by  the  magnitude  of  the 
deflection  of  the  magnetic  needle;  Definition  of  electro-magnets  .  12 

Expression  of  the  magnitude  of  the  magnetizing  force  of  the  current; 
Remanent  or  residual  magnetism;  Properties  of  an  electro- magnet; 
Flow  of  the  magnetic  lines  of  force;  Magnetic  field  .  .  .  .13 

Direction  and  magnitude  of  the  field-force;  Effect  of  the  electro-magnet 
upon  soft  iron;  Definition  of  permeability 14 

Magnitude  of  the  magnetic  induction;  The  solenoid      .         .         .         .15 

Induction. 

Definition  of  induction .        .        .15 

Primary,  inducing  or  main  current;  Secondary,  induced  or  induction- 
current  .  ....  16 


CONTENTS.  IX 

PAGE 

Direction  of  the  induced  current 17 

Electro- magnetic  alternating  actions;  Hand-rule  for  following  the 
direction  of  the  induced  current 18 

Fundamental  Principles  of  Electro-Technics. 

Electric  units 18 

Comparison  of  the  electric  current  with  a  current  of  water  .         .  19 

Definition  of  current-strength;    The  coulomb;    The  ampere;  Electro- 
motive force  or  tension          .........     20 

The  volt;  Difference  of  electro-motive  force  or  difference  of  potential; 

The  volt-ampere,  or  watt;  Unit  of  electrical  work;  Electric  resistance.     21 
Electric  resistance  of  the. current;  The  ohm;  Law  of  Ohm;  Equations; 

Examples  to  equations 22 

Internal  and  external  resistance;  Decrease  in  electro-motive  force        .     23 
Proportion  of  the  current-strength  to  the  resistance  of  the  current; 
Equation  for  calculating  the  decreasing  electro-motive  force;  Im- 
pressed electro-motive  force;  Specific  resistances        .         .         .         .24 
Specific  resistances  and  coefficient  of  temperature  of  the  metals  .         .     25 
(Tbefftcient  of  temperature;  Law  of  Kirchhoff;  Branching  or  distrib- 
uting the  current;  Main  wire  and  branch  wires 26 

Summary  of  Kirchhoff 's  law    .........     27 

Law  of  Joule 28 

Friction  a  I  Electricity . 
Idio-electrics      ............     28 

Non-electrics;  Good  and  bad  conductors;  Electroscope;  Kinds  of  elec- 
tricity .............  29 

Contact  Electricity. 

Generation  of  a  current  of  electricity  by  the  contact  of  various  metals; 
Potential;  Difference  of  potential;  Series  of  the  electro-motive  force 
of  the  metals 30 

Galvanic  current  or  hydro-electric  current;  Galvanic  element  or  voltaic 
cell 31 

Fundamental  Chemical  Principles. 
Action  of  moist  air  upon  bright  iron  or  steel;  Action  of  heat  upon  red 

oxide  of  mercury;  Synthetic  and  analytical  chemical  processes  .         .     32 
Law  of  the  conservation  of  matter;  Chemical  elements;   Molecules; 

Atoms 33 

Atomic  weights;  Symbols  and  their  formation 34 

Table  of  the  atomic  weights  of  the  most  important  chemical  elements, 
together  with  their  symbols  and  atomic  weights;  Valence  of  the 

elements 36 

Equivalent  weights  or  combining  weights      .         .         .         .         .         -37 
Arrangement  of  the  most  important  elements  according  to  their  va- 
lence; Metals  and  non-metals  and  their  classification.         .         .         .38 


X  CONTENTS. 

PAGE 

Metalloids;  Properties  of  metals  and  non-metals  .  .  .  .  .30 
Acids,  bases,  salts;  Great  affinity  of  the  elements  for  oxygen  .  .  40 
Acids  and  their  properties;  Haloid  acids;  Oxy-acids;  Bases;  Hydroxyl 

group;  Salts  and  their  properties 41 

Neutralization;  Reagent  papers        ........     42 

Formation  of  new  products  by  the  neutralization  between  acids  and 

bases       .............     43 

Formation  of  salts  from  the  acids;  Neutral  salts      .         .         .         .         .44 

Acid  salts;  Equations  showing  the  difference  between  neutral  and  acid 

salts;  Nomenclature  of  salts  ..........     45 

Fundamental  Principles  of  Electro-Chemistry. 

Electrolytes;  Conductors  and  non-conductors;  Conductors  of  the  first, 

and  of  the  second,  class 46 

Electrolysis;  Electrodes;  tons;  Cations;  Anions;  Properties  of  the  ions.     47 
Theory  of  solutions;  A  solution  not  merely  a  mechanical  mixture;  Vari- 
ous kinds  of  solutions    ..........     48 

Experiment  with  cupric  sulphate  solution;  Law  followed  by  the  gases; 

Osmotic  pressure 49 

Electrolytic  dissociation;    Clausius'    theory;    Raoult's  method  of   de- 
termining the  molecular  weights  of  dissolved  bodies  .         .         .         .50 
Discovery,  by  Arrhenius,  regarding  the  conductivity  of  solutions        .     51 
Migration   of  the   ions;    Energy;    Definition   of  energy;    Mechanical 

work 52 

Force  and  counter-force;  Law  of  the  conservation  of  force  and  work  .  53 
Processes  on  the  electrodes;  Electrolysis  of  a  solution  of  potassium 

disulphate 54 

Electrolysis  of  very  dilute  hydrochloric  acid,  and  of  sodium  hydroxide.     55 

Electrolysis  of  a  solution  of  cupric  sulphate 56 

Electrolysis  of  a  silver  bath  containing  potassium-silver  cyanide  .         .     57 
Laws  of  Faraday       ...........     58 

Proportion  of  the  quantity  of  substances  which  is  separated  on  the 

electrodes,  to  the  strength  of  the  electric  current        .         .         .         -59 
Second  law  of  Faraday  as  expressed  by  v.  Helmholz;  Eleptro-chemi- 
cal  equivalent,  and  its  definition  ........     60 

Table  of  electro-chemical  equivalents:  Solution-tension  of  metals.         .     61 
Osmotic  theory  of  the  production  of  the  current,  according  to  Nernst; 
Process  which  takes  places  in  a  cell     .         .         .         .    '    .         .         .63 

Determination  of  the  electro-motive  force  of  a  cell        .         .         .         .64 

Additional  chemical  processes  which  take  place  in  a  cell;  Polarization 
and  its  occurrence.         .         .         .         .         .         .         ......         .         .65 

Counter-current  or  polarization-current  ...         .;.-      .        ...     66 

Origin  of  the  electro-motive  force  of  the  polarization-current;  Decom- 
position-pressure     .,     .        .        .67 

Decomposition-values  of  solutions;  Velocity  of  ions  .  .  •  .  *. . .  .68 
Transport-values  of  the  ions  .  .  .  .  .  .  ..  .  .  ...  .  69 


CONTENTS.  XI 


III. 

SOURCES  OF  CURRENT. 


CHAPTER  III. 

VOLTAIC  CELLS,  THERMO-PILES,  DYNAMO-ELECTRIC  MACHINES, 
ACCUMULATORS. 

Voltaic  cells;  Conversion  of  chemical  energy  into  electrical  energy; 

Inconstant  cells 70 

Constant  cells;  Voltaic  pile;  Trough  battery;  Local  action;  Amalga- 
mation             ...     71 

Smee  cell  .............     72 

Avoidance  of  polarization;  Daniell  cell 73 

Meidinger  cell  ............     74 

Bunsen  cell;  Artificial  carbon  ..........     75 

Processes  in  the  Bunsen  cell;  Forms  of  Bunsen  cells    .         .         .         .76 

Improved  Bunsen  cell;  Location  of  Bunsen  cells  .....     78 

Dupre's  substitute  for  sulphuric  and  nitric  acids  for  filling  cells     .         .     79 
Treatment  of  Bunsen  cells         .         .         .         .         .         .         .         .         .80 

Advisability  of  having  duplicate  set  of  porous  clay  cups;  Renewal  of 
the  acid;  Leclanche  cell         .........     81 

Cupric  oxide  cell 82 

Cupron  cell        ............    83 

Plunge  batteries        , 84 

Plunge  battery  constructed  by  Fein 85 

Stoehrer's  plunge  battery;  Dr.  G.  Langbein's  plunge  battery       .         .     86 

Bichromate  cell;  Coupling  cells 87 

Coupling  for  electro-motive  force;  Coupling  for  quantity  of  current,  or 

parallel  coupling;  Mixed  coupling  or  group  coupling.         .         .         .89 
Thermo-electric  piles;  Discovery  by  Prof.  Seebeck        .         .         .         .90 

Noe's  and  Clamond's  thermo-electric  piles 91 

Giilcher's  thermo-electric  pile  .         .         .         .         .         .         .         .92 

Dynamo-electric  machines 93 

Fundamental  principle  of  dynamo-electric  machines      .         .         .         -94 
Windings;  Armature         ..........     95 

Separate  parts  of  the  dynamo-machine;  The  frame;  Magnetic  winding 

or  field  winding;  Two-polar  and  four-polar  type  of  dynamo        .         .     96 
Remanent  magnetism;  Self  excitation;  Foreign  or  separate  excitation; 
Armature  or  inductor;  Ring  armature;  Drum  armature;  Ring  arma- 
ture winding ............     97 

Drum  armature  winding 98 

Chief  difference  between  the  modes  of  winding      .         .         .         .         -99 
Slotted  armature;  Commutator        .         .         .         .         .  .         .  100 


Xll  CONTENTS. 

PAGE 

Brushes;  Choice  of  material  for  the  brushes;  Copper  and  brass  gauze 
brushes  .............  101 

Boudreaux  brushes;  Brush  holders;  Brush  rocker          ....  102 

Direct    current    dynamos;     Series    wound    machines;     Shunt-wound 

dynamo 103 

Two-pole  wound  dynamos 104 

Compound -wound  dynamos      .........  105 

Multi-polar  type  of  dynamo  manufactured    by  The   Hanson   &   Van 

Winkle  Co.,  and  its  armature 106 

Motor-generator  sets  manufactured  by  the  same  firm     ....  109 

Data  for  the  most  suitable  machine no 

Secondary  cells  (accumulators);  Planters  practical  application  of  ac- 
cumulators, and  his  accumulator in 

Use  of  lead  grids  by  Faure;  Chemical  processes  in  the  accumulator; 
Elb's  theory.         .         .         .         .         .         .         .         .         .         .         .112 

Liebenow's  theory;  Common  form  of  an  accumulator;  Maintenance  of 
accumulators.         .         .         .         ,         .         .         .         .         .         .         .116 

Mode  of  charging  a  cell 117 

Coupling  accumulators;  Ampere  hours  capacity      .         .         .         .         .118 


IV. 
PRACTICAL  PART. 


CHAPTER  IV. 
ARRANGEMENT  OF  ELECTRO-PLATING  ESTABLISHMENTS  IN  GENERAL. 

Light  and  ventilation  in  plating  rooms 119 

Heating  the  plating  room 120 

Renewal  of  water;  Floors  of  plating  rooms 121 

Size  of  plating  rooms;  Grinding  and  polishing  rooms     ....  122 

Exhaust  fans 123 

Distance  between  machines;  Transmission      .         .         .         .         .         .  124 

Electro-Plating  Arrangements  in  Particular. 

Parts  of  the  actual  electro-plating  plant;  Current  density        .         .         .  124 
Electro-chemical  equivalent  of  the  ampere-hour;  Determination  of  the 

quantity  of  deposit  and  the  time  required     ......  126 

Determination  of  the  current-output  ** 127 

Electro-motive  force  in  the  bath;  Determination  of  the  resistance  of 

the  electrolyte 128 

Electro-motive  counter  force  of  polarization    ......  130 

Determination  of  the  electro-motive  counter-force 131 

Scattering  of  the  current  lines 132 


CONTENTS.  Xlll 

PAGE 
A.    INSTALLATION  WITH  CELLS. 

Coupling  of  cells 132 

Examples  of  coupling  ..........  133 

Current  regulation 135 

Current  regulator,  resistance  board,  or  rheostat;  Conditions  upon 

which  the  action  of  the  resistance  board  is  based  .  .  .  .  136 
Modes  of  coupling  the  resistance  board  .......  137 

Current  indicator;  Galvanometer 138 

The  Hanson  &  Van  Winkle  patent  underwriters'  rheostat  .  .  .  140 
The  Hanson  &  Van  Winkle  Co.'s  special  rheostat  ....  141 
Indications  made  by  the  galvanometer;  Validity  of  the  deductions 

drawn  from  the  position  of  the  needle.         ......  143 

Means  of  recognizing  the  polarity  of  the  current;  Measuring  instru- 
ments; Ampere-meter  or  ammeter;  Voltmeter    .....  144 

Instmiments  constructed  according  to  Hummel's  patent        .         .         .  145 
The  Waverly  voltmeter    ..........  146 

The  Weston  ammeter;  Arrangement  of  the  switch-board,  and  ammeter 

with  a  bath  operated  by  means  of  a  battery;  Voltmeter  switch  .  .  147 
Scheme  showing  the  coupling  of  the  main  object-wire  and  of  the  main 

anode-wire,  together  with  the  resistance-boards,  the  voltmeter  switch 

and  two  baths , 148 

Dependence  of  the  current-density  on  the  electro-motive  force  .  .  151 
Conductors;  Most  suitable  material  for  conducting  the  current;  Loss  of 

electro-motive  force  caused  by  conductors 152 

Mounting  of  conductors;  Main  and  branch  conductors;  Dimensions  of 

conductors 153 

Connection  of  main  and  branch  conductors;  Tanks;  Welded  steel  tanks.  154 

Construction  of  wooden  tanks;  Lead-lined  tanks 155 

Cement-lined  tanks;  Stoneware  tanks      .         .        .         .         .         .         .  156 

Insulating  joint;  Conducting  fixtures;  Conducting  rods.         .         .         .  157 

Binding  posts  and  screws;  Arrangement  of  objects  and  anodes  in  the 

bath 158 

Supply  of  anodes;  Anode-hooks  ........  159 

Slinging  wires;  Protection  of  the  rods 160 

Apparatus  for  cleansing  and  rinsing;  Cleansing  the  objects  from  grease; 

Special  table  for  this  purpose  . 161 

Drying  the  objects    ...........  163 

Centrifugal  dryer 164 

B.    INSTALLATION  WITH  DYNAMO-ELECTRIC  MACHINES. 

Setting  up  and  running  a  dynamo;  Cause  of  most  of  the  troubles  with 
plating  dynamos  ...........  164 

Foundations  for  dynamos;  Mode  of  ascertaining  the  direction  of  rota- 
tion; Belting.  ...........  165 

Starting  up;  Proper  position  of  the  tips  of  the  brushes;  Adjustment  of 
the  brushes;  Lubrication;  Treatment  of  the  commutator  .  .  .  166 


XIV  CONTENTS. 

PAGE 

Choice  of  a  dynamo 167 

Impressed  electro-motive  force  of  the  dynamo;  Explanation  by  an  ex- 
ample of  the  choice  of  a  suitable  dynamo 168 

Destruction  of  an  excess  of  electro- motive  force     .....  169 

Advisability  of  using  several  dynamos  with  different  impressed  electro- 
motive forces.         ...........  170 

Principle  of  series-coupling  of  baths  illustrated;  Connection  of  the 
baths,  resistance  boards  and  measuring  instruments  to  a  shunt- 
wound  dynamo t  ...  171 

Parallel  coupling  and  series-coupling  of  dynamo-machines;  Rules  to 

be  observed  in  coupling  several  dynamos  in  parallel   .         .         .         .  172 
When  the  coupling  of  dynamos  in  series  may  become  necessary  .         .  174 
Ground  plan  of  an  electro-plating  plant  with  dynamo    ....  175 
Plating  room  and  method  of  connecting  dynamo,  tanks  and  instru- 
ments according  to  the  two-wire  system «.  179 

Three-wire  system  of  current  distribution;  Plating  room  wired  accord- 
ing to  this  system;  Switch  boards  .......  180 

C.    INSTALLATION  AND  ACCUMULATORS. 

Use  of  an  accumulator;  Dynamos  for  supplying  the  accumulator.         .  184 
On  what  the  magnitude  of  the  performance  of  an  accumulator  de- 
pends; Ampere-hour  capacity  of  an  accumulator;   Explanatory  ex- 
ample     .............  185 

Diagram  of  connections  for  using  storage  batteries  in  connection  with 
dynamos  .  .  ._ 186 

CHAPTER  V. 

PREPARATION  OF  THE  METALLIC  OBJECTS. 
A.  MECHANICAL  TREATMENT  PREVIOUS  TO  ELECTRO-PLATING. 

Nature  of  the  mechanical  treatment;  Formation  of  the  deposit  in  cor- 
respondence with  the  surface  of  the  basis-metal  .         .         .  .188 
Scratch-brushing;  Various  forms  of  brushes  .         .         ....  189 

Treatment  of  scratch-brushes 190 

Circular  scratch-brushes  and  their  construction  .....  191 
Various  kinds  of  brushes  suitable  for  the  different  operations  .  .  192 
The  sand-blast  and  its  use  in  cleaning;  Types  of  s*and-blast  .  .  .  193 
Cleaning  metallic  articles  in  the  tumbling  barrel  or  drum  .  .  .  194 
Adjustable  oblique  tumbling  barrel;  Grinding;  Grinding  wheels  and 

their  construction .         .         .         .  196 

Grinding  wheels  of  paste-board  and  of  cork  waste  .        .•       .        .         .  197 

Elastic  wheel;  Reform  wheel;  Emery  for  gluing 198 

Treatment  of  the  grinding  wheels;  Vienna  lime 199 

Removing  emery  and  glue  from  worn  leather-covered  wood  polishing 
wheels,  and  machine  for  that  purpose;  Grinding  lathes  .  .  .  200 


CONTENTS.  XV 

PAGE 

Belt  attachment  combined  with  a  double  grinding  lathe;  Types  of  elec- 
trically driven  grinding  motors    ........  202 

Execution  of  grinding  and  brushing;  Fiber  brushes       ....  204 

Grinding  iron  and  steel  articles 205 

Grinding  brass  and  copper  castings,   sheets  of  brass,  German  silver, 

copper  and  zinc;  Polishing 206 

Foot-lathe  for  polishing;    Union  canvas  wheel;    Universal  polishing 

wheel 207 

Walrine  wheel;  Types  of  polishing  lathes 208 

Independent  spindle  polishing  and  buffing  lathe     .....  210 
Electrically  driven  polishing  and  buffing  lathes      .  .         .         .211 

Belt-strapping  attachment;  Polishing  materials      .....  212 
Polishing  with  Vienna  lime;  Burnishing         ......  213 

B.    MECHANICAL  TREATMENT  DURING  AND  AFTER    ELECTRO-PLATING. 

Scratch-brushing  the  deposits,  and  its  object 213 

Porous  formation  of  the  deposit;  Effect  of  scratch-brushing;  Scratch- 
brushes  for  various  purposes;  Mode  of  operating  with  the  hand 
scratch-brush  ...........  214 

Scratch-brushing  with  the  lathe  brush;  Drying  the  finished  plated 
objects 215 

Freeing  nickel  objects  from  moisture;  Production  of  high  luster; 
PolisHing  deposits  of  nickel,  copper  and  brass,  gold,  silver  and 
platinum;  Operation  of  burnishing  .......  216 

Forms  of  burnishers;  Cleansing  the  polished  objects      ....  217 

CHEMICAL  TREATMENT. 

Pickling  and  dipping;  Pickle  for  cast-iron  and  wrought-iron  articles; 

Cleansing  badly  rusted  iron  articles 218 

Operation  of  pickling  cast-iron         ........  219 

Pickling  in  the  electrolytic  way        .         . 220 

Bath  for  electrolytic  pickling;  Removal  in  the  electrolytic  way  of  the 

layer  of  hard  solder  remaining  after  soldering  bicycle  frames      .         .  221 
Duration  of  pickling.         .         .         .         .         .         .         .         .         .         .  222 

Pickling  zinc  objects;  Cleansing  and  brightening  copper  and  its  alloys; 

Preliminary  pickle;  Bright  dipping  bath 223 

Use  of  potassium  cyanide  as  a  pickle;  Mat-dipping         ....  224 
Preparation  of  a  good  mat  dip;  Mixture  for  the  production  of  a  mat- 
grained  surface  by  pickling;  Main  points  to  be  observed  in  pickling.  225 

Absorbing  plant  for  escaping  acid  vapors 227 

Removal  of  grease  and  cleansing;  Materials  used  for  the  purpose.         .  228 
Preparation  of  lime  mixture  or  paste;  Electro-chemical  cleaning.         .  229 
Electro-chemical  cleaning  baths  and  their  application    ....  230 
Cleansing  objects  of  iron  and  steel,  copper,  bronze,  German  silver  and 
tombac 232 


XVI  CONTENTS. 


ELECTRO-PLATING  SOLUTIONS  (ELECTROLYTES,  BATHS). 

Solvents;  Spring  and  well  waters 233 

Distilled  water,  Rain  water;  Purity  of  chemicals;  Examples  of  differ- 
ence in  chemicals  ...........  234 

Concentration  of  the  baths;  Conclusions  which  may  be  drawn  from  the 

specific  gravity * 235 

Cause  of  dark  or  spotted  nickeling;   Difference  in  concentration  in 

summer  and  in  winter;  Agitation  of  the  baths 236 

Uneven  wearing  of  the  anodes 237 

Advantages  claimed  for  constant  agitation;  Cause  of  changes  in  con- 
centration of  the  baths  .         .         .         .         , 238 

Temperature  of  the  baths;  Boiling  the  baths,  and  utensils  for  the  pur- 
pose          ...  240 

Use  of  nickeled  kettles;  Dissolving  nickel  salts  soluble  with  difficulty; 

Working  the  bath  with  the  current;  Objections  to  this  process.         .  241 
Filtering  the  baths;  Prevention  of  impurities;  Choice  of  anodes  .         .  242 

Absorption  of  the  deposit 243 

Effect  of  the  current-density 244 

Current-output;  Reaction  of  the  baths 245 

General  qualifications  an  electro-plating  bath  should  possess         .         .  246 

CHAPTER  VI. 
DEPOSITION  OF  NICKEL  AND  COBALT. 

I.  DEPOSITION  OF  NICKEL. 
Growth  and  popularity  of  nickel  plating;  Properties  of  nickel        .         .  247 

Nickel  salts 248 

Conducting  salts 249 

Other  additions  to  nickel  baths;  Boric  acid 250 

Substitution  of  glycerin  for  water  in  the  preparation  of  nickel  baths  .  251 
Effect  of  current-density;  Electro-motive  force;  Reaction  of  nickel 

baths       .         .         .         .         ,        •  "'  v;;;        •••:•"•        •  •     ....-•••      •  252 

Formulas  for  nickel  baths        .         .         .        .....        .        .        .  253 

Baths  with  the  addition  of  chlorides        .         .        .        .        .        •         •  255 

Nickel  baths  containing  boric  acid .         .         .         .        .        .        .         .  256 

Nickel  baths  for  special  purposes;  For  copper  and  copper  alloys  .  .  258 
For  zinc;  Bath  yielding  a  very  fine  dark  nickeling  ....  259 

Black  nickeling 260 

Bath  for  iron  and  copper  alloys;  Baths  for  the  production  of  very  thick 

deposits '   .        ...         .         .  262 

Addition  of  carbon  disulphide  to  nickel  baths  ...  .  .  263 
Nickel  bath  without  nickel  salt;  Prepared  nickel  salts  .  .  .  .264 
Correction  of  the  reaction  of  nickel  baths;  Thick  deposits  in  hot 

nickel  baths 265 

Foerster's  experiments;  Dr.  George  Langbein's  experiments;  Quick 

nickeling;  Dr.  Kugel's  discovery 266 


CONTENTS.  XV11 

PAGE 

Thick  deposits  in  cold  nickel  baths  .         .         .         .  .         .  267 

Coehn  and  Siemens'  experiments  with  electrolytes  containing  nickel 
salts  and  magnesium  salts;  Nickel  anodes;  Elliptic  anodes  patented 
by  The  Hanson  &  Van  Winkle  Co.     .         .         .         .         .         .         .268 

Objection  to  the  use  of  insoluble  anodes          .         .         .         .         .         .  271 

Proportion  of  cast  to  rolled  anodes .         .  273 

Cause  of  a  reddish  tinge  on  the  anodes    .         .         .         .         .         .  274 

Uneven  solution  of  the  anodes;  Scattering  of  current  lines;   Execu- 
tion of  nickeling;  Removal  of  grease  from  the  objects        .         .         .  275 
Previous  coppering  or  brassing  of  certain  objects;  Security  against  rust.  276 
Nickeling  parts  of  bicycles;   Means  for  preventing  the  rusting  of  the 

basis-metal 277 

Over-nickeling  or  burning  and  means  of  avoiding  it  .         .         .  278 

Normal  deposition  and  criterion  for  judging  it;   Most  suitable  current- 
density  for  nickeling      ..........  279 

Advisability  of  the  use  of  a  voltmeter  and  ammeter,  as  well  as  of  a 

rheostat;  Production  of  a  very  thick  deposit;  Solid  nickeling     .         .  280 
Faulty  arrangement  of  anodes;  Suspension  of  the  objects       .         .         .  281 
Nickeling  of  cavities  and  profiled  objects;  Use  of  the  hand  anode;  Ex- 
periments in  nickeling  the  inside  of  brass  tubes  .....  282 

Polarization;  Reason  why  iron  requires  a  stronger  current  for  nickel- 
ing than  copper  alloys,  and  zinc  a  stronger  one  than  iron.         .         .  284 

Stripping  defective  nickeling 285 

Stripping  acid    ............  286 

Removal  of  the   nickel   coating  by  mechanical  means;    Stripping  by 

electrolysis 287 

Remedy  against  the  yellowish  tone  of  the  nickeling;  Defective  nickel- 
ing; Resume  of  the  principal  defects  which  may  occur  in  nickeling, 

and  remedies 288 

Refreshing  nickel  baths    .         .         .         .         .         .         .         .         .         .  290 

Treatment  of  the  articles  after  nickeling;  Polishing  nickel  deposits; 
Cleansing  polished  objects     .........  291 

Calculation  of  the  nickeling  operation 292 

Nickeling  small  and  cheap  objects  in  large  quantities     ....  293 

Types  of  mechanical  electro-plating  apparatus 295 

Lifting  device  for  raising  and  lowering  the  plating  barrel  .  .  .  297 
Nickeling  sheet-zinc;  Preliminary  grinding  or  polishing  the  sheets  .  298 
Construction  of  cloth  bobs;  Mode  of  polishing  the  sheets  .  .  .  299 
Automatic  polishing  machines  .  .  .  .  .  .  .  .  300 

Freeing  zinc  sheets  from  grease 301 

Nickeling  the  sheets;  Advantages  of  coppering  or  brassing  the  sheets.  302 
Dimensions  of  tanks  for  nickeling  the  sheets;  Anodes  for  nickeling 

sheet-zinc 304 

Alkalinity  of  the  baths  for  nickeling  sheet-zinc;  Polishing  the  nickeled 

sheets 305 

Nickeling  tin-plate,  copper  and  brass  sheets,  sheet-iron  and  sheet-steel.  306 


XV111  CONTENTS. 


Nickeling  wire 307 

Nickeling  knife-blades,  sharp  instruments,  etc.      .....  310 

Nickeling  skates;  Nickeling  soft  alloys  of  lead  and  tin  .         .         .         .311 

Nickeling  printing  plates;  Hard  nickeling  and  baths  for  that  purpose.  312 
Recovery  of  nickel  from  old  baths;  Deposition  of  nickel  alloys      .         .  314 
Nickel  bronze;  Deposit  of  German  silver        ......  315 

Examination  of  nickel  baths;  Determination  of  the  content  of  acid       .  316 
Methods  for  the  examination  of  baths;  Gravimetric  analysis;  Volu- 
metric analysis .         .  318 

Electrolytic  method  of  analysis,  and  apparatus  for  that  purpose     .         .  319 

2.    DEPOSITION  OF  COBALT. 

Properties  of  cobalt;  Baths  for  plating  with  cobalt;  Cobalting  copper 
plates  for  printing 323 

Determination  of  the  quantity  of  copper  dissolved  in  stripping  the  co- 
balt deposit  from  cobalted  copper  plates;  Warren's  cobalt  solution  .  324 

CHAPTER  VII. 
DEPOSITION  OF  COPPER,  BRASS  AND  BRONZE. 

I.  DEPOSITION  OF  COPPER. 
Properties  of  copper;  Copper  baths;  On  what  the  composition  of  these 

baths  depends 326 

Copper  cyanide  baths,   and    their   preparation;    Formation  of   cupric 

cyanide 327 

Stockmeyer's  experiments;  Hossauer's  copper  bath       ....  328 
Copper  baths  for  iron  and  steel  articles   .......  329 

Stockmeyer's  copper  bath 330 

Copper  baths  with  sulphate  of  copper  (blue  vitriol)         ....  331 

Use  of  cupro-cupric  sulphite  for  the  preparation  of  copper  baths;  Cop- 
per bath  recommended  by  Pfanhauser.         ......  332 

Copper  bath  for  small  zinc  objects;  Prepared  copper  salts      .         .         .  333 
Copper  baths  without  potassium  cyanide;  Bath  for  coppering  zinc  ob- 
jects; Weill's  copper  bath 334 

Walenn's  and  Gauduin's  copper  baths;  Tanks  for  potassium-copper 

cyanide  baths. 335 

Copper    anodes;    Formation    of   slime    on    the    anodes;  Execution  of 

copper-plating 336 

Causes  of  copper  baths  yielding  no  deposit  at  all  or  only  a  slight  one, 

and  their  remedies .         .         .  337 

Scouring  and  pickling  the  articles  to  be  coppered;  Treatment  of  de- 
fective places  of  the  deposit;  Washing  the  coppered  objects       .         .  338 
Prevention  of  stains;  O.  Schultz's  method  for  removing  hydrochloric 
acid  from  the  pores  and  preventing  the  formation  of  stains;  Polish- 
ing the  coppered  objects .  339 

Penetration  of  the  deposit  into  the  basis-metal;  Coppering  sheet-iron 
or  sheet-zinc;  Treatment  of  copper  baths  when  they  become  inactive.  340 


CONTENTS.  XIX 

PAGE 

Coppering  small  articles  in  quantities;  Inlaying  of  depressions  of  cop- 
pered art  castings  with  black 341 

Examination  of  copper  baths  containing  potassium  cyanide  .         .         .  342 
Determination  of  potassium  cyanide        .......  343 

Determination  of  copper  by  electrolysis 345 

Volumetric  determination  of  copper 346 

2.    DEPOSITION  OF  BRASS. 

Constitution  and  varieties  of  brass 348 

Behavior  of  brass  towards  acids;  Brass  baths,  their  composition  and 

preparation 349 

Rules  for  baths  containing  more  than  one  metal  in  solution;  Brass 

bath  according  to  Roseleur 350 

Other  brass  baths      ...........  351 

Use  of  cupro-cupric  sulphite  and  cuprous  oxide  for  the  preparation  of 

brass  baths 352 

Bath  for  brassing  zinc;  Bath  for  brassing  wrought  iron,  cast  iron  and 

steel 353 

Solution  for  transferring  any  copper-zinc  alloy  which  serves  as  anode; 

Irregular  working  of  fresh  baths;  Prepared  brass  salts  .  .  .  354 
Tanks  for  brass  baths;  Brass  anodes;  Execution  of  brassing;  On  what 

the  color  of  the  deposit  depends    .         .         .         .         .        .        .         .  355 

Formation  of  slime  on  the  anodes,  and  what  it  indicates       .         .         .  356 
Remedies  for  the  sluggish  formation  of  the  deposit        ....  357 

Effect  of  too  great  an  excess  of  potassium  cyanide;  Treatment  of  a 

brass  bath  that  has  not  been  used  for  some  time  ....  358 
Production  of  a  brass  deposit  which  is  to  show  a  tone  resembling  gold; 

Importance  of  the  distance  of  the  objects  to  be  brassed  from  the 

anodes 359 

Brassing  of  unground  iron  casting;   Examination  of  brass  baths;  De- 
termination of  free  potassium  cyanide  and  the  content  of  copper        .  360 
Volumetric  determination  of  zinc;  Deposits  of  tombac  ....  362 

Deposits  of  bronze    ...........  363 

Method  of  preparing  a  bronze  bath 364 

CHAPTER  VII. 

DEPOSITION  OF  SILVER. 
Properties  of  silver    ...........  365 

Silver  baths,  their  composition,  preparation  and  treatment    .        .         .  366 
Advantage  of  silver  baths  prepared  with  silver  chloride.         .         .         .  367 

Silver  bath  for  a  heavy  deposit  (silvering  by  weight);  Preparation  of  a 

bath  with  silver  chloride;  Preparation  of  silver  chloride      .         .        .  368 
Preparation  of  a  bath  with  silver  cyanide;  Preparation  of  silver  cyanide.  369 
Silver  bath  for  ordinary  electro-silvering;  Tanks  for  silver  baths;  Treat- 
ment of  the  silver  baths;  Silver  anodes;  Potassium  cyanide  required 
for  the  bath 370 


XX  CONTENTS. 


Indication  of  the  presence  of  too  much  or  not  enough  potassium  cyanide.  371 
The  behavior  and  appearance  of  the  anodes  as  criteria  of  the  content  of 
potassium  cyanide  in  the  bath;  Regulating  the  content  of  potassium 

cyanide 372 

Keeping  the  bath  constant  by  silver  anodes 373 

Proper  treatment  of  baths  made  with  silver  chloride;  Gradual  thicken- 
ing of  the  baths 374 

Determination  of  the  proper  proportion  of  silver  and  excess  of  potas- 
sium cyanide  in  the  bath;  Agitation  of  silver  baths;  Contrivances  to 

keep  the  articles  in  gentle  motion 375 

Addition  of  certain  substances  to  silver  baths;  Preparations  for  bright 

plating .377 

Yellow  tone  of  silvering .         .  .  379 

Silver  alloys;  Areas  silver-plating 380 

Experiments  in  areas  silver-plating 381 

Execution  of  silver-plating;    Silver-plating  by  weight;  Freeing  from 

grease;  Pickling  and  rubbing;  Amalgamating  (quicking).         .         .  382 
Slinging  wires;  Methods  of  depositing  an  extra  heavy  coating  of  silver 

on  the  convex  surfaces  of  spoons  and  forks 383 

Silver-plating  the  steel  blades  of  table  knives.         .....  385 

Determination  of  weight  of  deposit          .         .         .         .         .         .         .  386 

Roseleur's  plating  balance 388 

Plating  balance,  together  with  rheostat,  voltmeter  and  silver  bath        .  390 
Voltametric  balance;  Copper  voltameter          ......  392 

Advantages  and  disadvantages  of  the  voltametric  balance      .         .         .  393. 

Neubeck's  combination    .         . 394 

Voltametric  controlling  apparatus 396 

Calculation  of  the  weight  of   the    silver   deposit    from    the    current- 
strength  used 39& 

Mat  silver 400 

Polishing  the  deposits;    Ordinary  silver-plating;    Quicking  solution; 

Direct  silvering  of  Britannia,  tin,  German  silver        .         .'    •  .         .  401 
Australian  patent  for  directly  silver-plating  iron  and  steel;  Stopping- 
off,  and  varnish  for  that  purpose  .         .         .        .       •„        .         .       -.  402 

Special  application  of  electro-silvering;  Silvering  of  fine  copper  wire; 
Incrustations  with  silver  and  gold        .        ;      ,..       ....         .  403 

Imitation  of  niel  or  nielled  silvering;  Nielling  upon  brass     .         .         .  404 
Old  (antique)  silvering;  Oxidized  silver.        .        .        .  .         .  405 

Brown  tone  on  silver 406 

Yellow  color  on  silvered  articles:  Stripping  silvered  articles.         .         .  407 
Determination    of    silver-plating;    Process   for    the    determination    of 

genuine  silvering  used  by  the  German  custom-house  officers     .         .  408 
Examination  of  silver  baths;  Determination  of  free  potassium  cyanide, 
and  of  potassium  carbonate  .         .         .         .        .        .       .,        ,-       .  409 

Calculation  of  the  quantity  of   barium  cyanide  required  for  the  con- 
version of  the  quantity  of  potassium  carbonate  found.        .        .        .  410 


CONTENTS.  XXI 

PAGE 

Table  for  the  use  of  a  20^  per  cent,  barium  cyanide  solution;  Deter- 
mination of  the  silver  by  the  electrolytic  method        .         .         .         .411 
Recovery  of  silver  from  old  silver  baths,  etc.         .         ...         .         .  412 

CHAPTER  IX. 
DEPOSITION  OF  GOLD. 

Occurrence  of  gold;  Properties  of  gold;  Mode  of  expressing  the  fine- 
ness of  gold;  Testing  gold  by  means  of  the  touch-stone     .         .         ,  415 
Shell-gold  or  painters'  gold;  Gold  baths  their  composition,  prepara- 
tion and  treatment 416 

Baths  for  cold  gilding;  Effect  of  too  large  an  excess  of  potassium  cyanide.  417 
Bath  with  yellow  prussiate  of  potash  for  cold  gilding     ....  418 

Baths  for  hot  gilding 419 

Preparation  of  gold  baths  with  the  assistance  of  the  electric  current     .  420 
Gold  anodes;  Management  of  gold  baths;  Use  of  insoluble  platinum 

anodes;  Use  of  steel  anodes  and  experiments  with  them    .         .         .  421 
Advantages  claimed  for  steel  anodes;  Use  of  carbon  anodes;  Platinum 

anodes  for  coloring  the  deposit 423 

Cause  of  unsightly  and  spotted  deposits;  Tanks  for  gold  baths      .         .  424 

Heating  the  baths .  425 

Execution  of  gold-plating;  Gilding  without  a  battery;  Preparation  of 

the  articles  for  gilding 426 

Current-strength  for  gilding;  Agitation  of  the  objects  in  the  bath        .  427 
Gilding  the  inner  surfaces  of  hollow-ware;  Process  of  gold-plating  in 
the  cold,  and  in  the  hot,  bath       ........  428 

Polishing  the  gold  deposits  •     .         . ,  429 

Red  gilding;    Determination  of  the  content  of   copper  required  for 
obtaining  a  beautiful  red  gold        ........  430 

Plating  rings,  watch  chains,  and  other  objects  of  base  metal  with  red 
gold;  Green  gilding       ..........  431 

Rose-color  gilding;  Rose  gold  solution 432 

Method  of  gilding  which  is  a  combination  of  fire-gilding  with  electro- 
deposition       433 

Mat  gilding;  Matting  with  the  sand  blast  and  by  chemical  or  electro- 
chemical means      ...........  434 

Coloring  of  the  gilding 435 

Gilder's  wax;  Process  to  give  gilded  articles  a  beautiful,  rich  appear- 
ance  436 

Method  of  improving  bad  tones  of  gilding;  Incrustations  with  gold; 
Gilding  of  metallic  wire  and  gauze;  J.  W.  Spaeth's  machine  for  this 

purpose 437 

Stripping  gold  from  gilded  articles;  Electrolytic  smoothing  and  polish- 
ing scratched  or  rubbed  rings 440 

Determination  of  genuine  gilding;  Examination  of  gold  baths;   De- 
termination of  gold  by  the  electrolytic  method    .  .        .         .  441 
Recovery  of  gold  from  gold  baths,  etc.    .......  442 


XX11  CONTENTS. 

CHAPTER  X. 
DEPOSITION  OF  PLATINUM  AND  PALLADIUM. 

I.  DEPOSITION  OF  PLATINUM. 

Properties  of  platinum;  Platinum  baths,  their  composition,  prepara- 
tion and  treatment 444 

Boettger's  bath;  Preparation  of  platoso-ammonium  chloride;  Platinum 
bath  patented  by  the  Bright  Platinum  Plating  Co.;  Jordis's  platinum 

bath        .  445 

Management  of  platinum  baths;  Execution  of  platinum  plating     .         .  446 
Production  of  heavy  deposits;   Process  for  plating  directly,   without 
previous    coppering,    iron,    nickel,    cobalt,    and    their    alloys    with 
platinum         ............  447 

Recovery  of  platinum  from  platinum  solutions 448 

2.    DEPOSITION  OF  PALLADIUM. 

Properties  of  palladium 448 

Bertrand's  palladium  bath;  Pilet's  bath  for  plating  watch  movements.  449 

CHAPTER  XI. 

DEPOSITION  OF  TIN,   ZINC,   LEAD,   AND  IRON. 
I.     DEPOSITION  OF  TIN. 

Properties  of  tin;  Moire  metallique  on  tin;  Tin  baths,  their  composi- 
tion, preparation  and  treatment 450 

Tinning  of  objects  of  zinc,  copper,  and  brass;  Experiments  with  Sal- 
zede's  bronze  bath 451 

Neubeck's  bath;  Management  of  tin  baths;  Process  of  tin-plating        .  452 

2.    DEPOSITION  OF  ZINC. 

Properties  of  zinc 453 

Value  of  electro-zincking 454 

Comparative  experiments  regarding  zincking  by  the  hot  process  and 
by  electro-deposition;  Disadvantages  of  hot  galvanizing;  Loss  of  zinc 

in  electro-zincking 455 

Drawbacks  of  both  processes;  Preece's  test  for  judging  the  thickness 
of  the  coating  of  zinc  obtained  by  hot  galvanizing;  Burgess's  method 
of  testing  the  power  of  resistance  of  coatings  obtained  by  electro- 
zincking  456 

Zinc  baths;  Dr.  Alexander's  patented  zinc  bath 458 

Decision  of  the  Circuit  Court  of  the  United  States  for  the  District  of 
New  Jersey  in  regard  to  the  Alexander  patent;  Recent  investigations 
regarding  the  electrolysis  of  zinc;  Regenerative  process     .         .         .  450 
Addition  of  aluminium-magnesium  alloy  and  of  dextrose  to  zinc  baths.  460 
Addition  of  pyridine,  and  of  glucosides;  Formula  for  an  alkaline  zinc 

bath .         .         .461 

Formulas  for  zinc  baths;  Importance  of  using  zinc  salts  free  from  other 
metals 462; 


CONTENTS.  XX111 

PAGE 

Zinc  anodes;  Treatment  of  zinc  baths 463 

Loss  of  zinc  by  the  formation  of  basic  zinc  salts;  Heating  the  baths  for 

strongly  profiled  objects        ....*.....  464 
Tanks  for  zinc  baths;  Execution  of  zincking  ......  465 

Zincking  of  sheet  iron 466 

Zincking  of  pipes      ...........  467 

Zincking  of  wrought  iron  girders,  "Y-iron,  \J-iron,  L-iron,  etc.;  Pro- 
filed anodes    ............  468 

Zincking  of  wire,  steel  tapes,  cords,  etc.         ......  469 

Zincking  of  screws,  nuts,  rivets,  nails,  tacks,  etc.;  Zinc  alloys,  and 
their  deposition  ...........  471 

3.    DEPOSITION  OF  LEAD. 

Properties  of   lead;    Lead  baths,  their  composition  and  preparation; 

Anodes  for  lead  baths 472 

Metallo-chromes  (Nobili's  rings,  iridescent  colors,  electrochromy)       .  473 

4.    DEPOSITION  OF  IRON   (STEELING)  . 

Principal  practical  use  of  the  electro-deposition  of  iron;  Iron  (steel) 
baths,  their  composition  and  preparation     ......  475 

Management  of  iron  baths       .........  476 

Execution  of  steeling 477 

CHAPTER  XII. 
DEPOSITION  OF  ANTIMONY,  ARSENIC,  ALUMINIUM. 

I.  DEPOSITION  OF  ANTIMONY. 

Properties  of  antimony;  Antimony  baths,  their  composition  and  pre- 
paration; Explosive  power  of  antimony  deposits 478 

Non-explosive  deposit  of  antimony;  Antimony  bath  which  yields  good 
results 479 

2.    DEPOSITION  OF  ARSENIC.  • 

Properties  of  arsenic;   Arsenic  baths,  their  composition,  preparation 

and  treatment 479 

Cause  of  defective  deposits        .         .         .         .         .         .         .         .         .  480 

Solutions  for  coloring  articles  black 481 

3.    DEPOSITION  OF  ALUMINIUM. 

Non-feasibility  of  depositions  of  aluminium  from  aqueous  solutions  of 
its  salts;  Aluminium  baths  offered  by  dealers,  and  the  results  of  test- 
ing them 483 

4.    DEPOSITION  UPON  ALUMINIUM. 

Difficulties  met  with  in  the  electro-deposition  of  other  metals  upon 
aluminium;  Behavior  of  aluminium  towards  the  usual  cleansing 
agents  .............  484 


XXIV  CONTENTS. 


Coppering  aluminium  previous  to  plating  and  copper  bath  for  this  pur- 
pose; Villon's  process  of  plating  aluminium;  Prof.  Nees's  process; 
Burgess  and  Hambuecnen's  method 485 

Gottig's  process;  Electro-deposits  upon  aluminium  produced  by  the 
Mannesmann  Pipe  Works,  Germany  .  .  .  .  '  .  .  .  486 

CHAPTER  XIII. 

DEPOSITION  BY  CONTACT,  BY  BOILING,  AND  BY  FRICTION. 
Theory  of  contact-deposition;  Deposits  by  immersion  or  boiling;  Plat- 
ing by  means  of  a  brush  or  by  friction.         ......  487 

Limits  of  the  application  of  the  contact-process;    Drawbacks  of  the 
process   .............  488 

Contact-metals;  Properties  of  the  electrolytes  for  the  contact-process  .  489 
Means  of  increasing  the  conductivity  of   the  electrolytes  containing 
potassium  cyanide;  Promotion  of  the  attack  of  the  contact-metal; 
Plating  small  objects  in  quantities;    Useless  reduction  of  metal  in 

contact-deposition          .         .         .* 490 

Methods  to  avoid  the  reduction  of  metal  on  the  wrong  place;  Defects 
of  the  contact-process;  Nickeling  by  contact  and  boiling;  Stolba's 

process  of  nickeling 491 

Processes  for  nickeling  small  articles;    Use  of  aluminium-contact  in 

place  of  zinc-contact 492 

Darlay's  patented  process  of  nickeling    .......  493 

Chemical  process  of  Darlay's  electrolyte;    Cobalting  by  contact  and 

boiling    .         .         .       ~7~ 494 

Coppering   by  contact  and  dipping;    Liidersdorff's  solution;  Bacco's 

copper  bath 495 

Darlay's  patented  bath      ..........  496 

Chemical  process  of  Darlay's  formula;  Brush  coppering        .         .         .  497 
Coppering  iron  and  steel  objects,  steel  pens,  needles'  eyes,  etc.;  Brass- 
ing by  contact;  Darlay's  bath 498 

Silvering  by -contact,  immersion  and  friction;  Bath  for  contact-silver- 
ing of  copper  and  brass  objects 499 

Darlay's  patented  bath;  Silvering  by  immersion  and  solution  for  this 
purpose  .............  5°o 

Preparation  of  solution  of  sodium  sulphite       ......  501 

Ebermayer's  silver  immersion-bath;    Process  of  coating  with  a  thin 

film  of  silver  small  articles,  such  as  hooks  and  eyes,  pins,  etc.  .         .  503 
Cold  silvering  with  paste;  Composition  of  the  argentiferous  paste        .  504 
Graining;  Process  of  graining  parts  of  watches      .         .         .         .         .  505 

Preparations  for  graining;  Preparation  of  silver  powder        .         .         .  506 
Composition  of  resist        .         .         .         .         ...         .         .  .  507 

Gilding  by  contact,  by  immersion,  and  by  friction;  Formulas  for  con- 
tact gold  baths 508 

Gilding  by  immersion  (without  battery  or  contact)  and  formulas  for 
this  purpose 509 


CONTENTS.  XXV 

PAGE 

Gilding  by  friction;  Reddish  gilding  by  friction;  Solution  for  gilding 
by  friction  ............  510 

Platinizing  by  contact;  Tinning  by  contact  and  by  boiling;  Baths  for 
tinning  by  contact 511 

Zilken's  patented  bath  for  tinning  by  contact;  Darlay's  cold  tin  bath; 
Tinning  solution  for  iron  and  steel  articles.  .....  512 

Tinning  solutions  for  small  brass  and  copper  articles      ....  513 

A  characteristic  method  of  tinning  by  Stolba;  Zincking  by  contact, 
and  solution  for  this  purpose;  Darlay's  bath;  Process  for  coating 
brass  and  copper  with  a  bright  layer  of  zinc 514 

Deposition  of  antimony  and  of  arsenic  by  immersion     ....  515 

CHAPTER  XIV. 
COLORING  OF  METALS. 

Means  by  which  metal  coloring  may  be  effected;  Requirements  for  the 

practice  of  coloring 516 

Coloring  of  copper;  Production  of  all  shades  from  the  pale  red  of  cop- 
per to  a  dark  chestnut-brown;  Brown  color  on  copper;  Brown  layer 
of  cuprous  oxide  on  copper;  Brown  of  various  shades  on  copper         .  518 
Brown  on  copper  by  the   Chinese  process;    Gold-yellow  on  copper; 

Manduit's  process  of  bronzing  copper;  Yellowish-brown  on  copper  .  519 
Dark  brown  to  black  on  copper;   Red  to  violet  shades  on  copper; 

Cuivre-fumk ' 520 

Black  color  on  copper;  Mat-black  on  copper  ......  521 

Patina;  Definitions  of  patina  and  patinizing;   Artificial  patina:   Pro- 
cesses of  patinizing         ..........  522 

Donath's  process;  Imitation  of  genuine  green  patina     ....  523 

Blue-green  patina;   Brown  patina;   Patina  for  copper  and  brass;  Steel 

gray  on  copper 524 

Various  colors  upon  massive  copper;  Coloring  brass  and  bronzes.         .  525 
Lustrous  black  on  brass;  Black  color  on  brass  optical  instruments         .  526 
Steel-gray  on  brass;  Silver  color  on  brass;  Pale  gold  color  on  brass; 
Straw  color,  to  brown,  through  golden  yellow,  and  tombac  color  on 
brass;  Color  resembling  gold  on  brass.         ......  527 

Brown  color  called  bronze  Barbedienne  on  brass 528 

Coloring  bronze  articles  dead-yellow  or  clay-yellow;  Coloring  brass 
articles  in  large  quantities  brown  by  boiling;  Violet  and  cornflower 

blue  on  brass 529 

Ebermayer's  experiments  in  coloring  brass    ......  530 

Coloring  zinc;  Black  on  zinc 531 

Gray,  yellow,  brown  to  black  colors  upon  zinc;  Brown  patina  on  zinc; 
Various  colors  on  zinc  ..........  532 

Gray  coating  on  zinc;  Bronzing,  and  yellow  shades  on  zinc;  Coloring 
iron;  Browning  gun  barrels;  Lustrous  black  on  iron.         .         .         .  533 

Meritens'  process  for  obtaining  a  bright  black  color  on  iron.         .         .  534 


XXVI  CONTENTS. 

PAGE 

Mat  black  coating  upon  clock  cases  of  iron  and  steel — Swiss  mat;  Blue 
color  on  iron  and  steel;  Brown-black  coating  with  bronze  luster  on 
iron;  To  give  iron  a  silvery  appearance  with  high  luster  .  .  .  535 

Coloring  of  tin;  Bronze-like  patina  on  tin;  Sepia-brown  tone  upon 
tin;  Dark  coloration  upon  tin;  Electrochroma 536 

CHAPTER  XV. 
LACQUERING. 

Application  of  lacquer;  Drying  the  lacquered  objects     ....  538 
Development  in  the  art  of  lacquer  making,  and  most  noted  improve- 
ments in  lacquers;  Pyroxylitie  lacquers,  and  their  properties     .         .  539 

Lacquering  by  dipping .  540 

Appearance  of  rainbow  colors  upon  objects  lacquered  with  pyroxyline 
lacquer;    Production  of   various  shades  of   color;    Special  invisible 
lacquer  for  ornamental  cast  and  chased  interior  grille,  rail  and  en- 
closure work.         ...........  541 

Satin  finish  lacquer;   Dip  lacquer  for  pickled  castings  to  be  copper- 
plated  and  oxidized        ..........  542 

Helios  dip  lacquer;  Old  brass  or  brush-brass  finishes     ....  543 

Brush-brass  finish  lacquers 544 

Egyptian  brush-brass  dip  lacquer  and  brush-brass  thinner;  Brass  bed- 
stead lacquering 545 

Dead  black  lacquers .         .         .         .         .  .        .         .         .         .  546 

Dead  black  lacquer  as  a  substitute  for  Bower-Barff        ....  547 

Spraying  of  lacquers;  The  spraying  machine  and  its  application  .         .  548 
Equipment  to  be  used       ..........  549 

Management  of  lacquers  for  spraying 550 

Lacquers  for  spraying  manufactured  by  The  Egyptian  Lacquer  Manu- 
facturing Co.;  Spraying  black  lacquers;  Priming  lacquer  .  .  551 

Water-dip  lacquers  and  their  use 553 

Points  to  be  followed  when  using  water-dip  lacquers      ....  554 

CHAPTER  XVI. 
HYGIENIC  RULES  FOR  THE  WORKSHOP. 

Neutralization  of  the  action  of  acid  upon  the  enamel  of  the  teeth  and 
the  mucous  membranes  of  the  mouth  and  throat;  Protection  against 
the  corrosive  effect  of  lime  and  caustic  lye;  Vessels  used  in  the 
establishment  not  to  be  used  for  drinking  purposes  ....  555 

Precautions  in  handling  potassium  cyanide  and  its  solutions;  Sensi- 
tiveness of  many  persons  to  nickel  solutions;  Poisoning  by  prussic 
acid,  potassium  cyanide  and  by  cyanide  combinations;  Poisoning  by 
copper  salts 556 

Poisoning  by  lead  salts;  by  alkalies;  by  mercury  salts;  by  sulphuretted 
hydrogen;  by  chlorine,  sulphurous  acid,  nitrous  and  hyponitric  gases.  557 


CONTENTS.  XXV11 

PAGE 

CHAPTER  XVII. 
GALVANOPLASTY  (REPRODUCTION). 

Definition  of  galvanoplasty  proper;  Application  of  galvanoplasty;  In- 
vention of  the  process    ..........  558 

I.    GALVANOPLASTY  IN  COPPER. 

Properties  of  copper  deposited  by  electrolysis;    Composition   of   the 

bath  for  depositing  copper;  Investigations  by  Hiibl  and  by  Forster.  559 
Formation  of  spongy  and  sandy  deposits;    Investigations  by  Mylius 

and  Fromm,  and  by  Lenz  and  Soret 560 

Classification  of  the  processes  used  in  galvanoplasty;  Galvanoplastic 

deposition  in  the  cell  apparatus;  Simple  apparatus  frequently  used     .  561 
Large  apparatus;  French  form  of  cell  apparatus     .....  562 

German  form  of  cell  apparatus 563 

Copper  bath  for  the  cell  apparatus  .        .         .         .         .         .         .  *       .  564 

Freeing  the  bath  from  an  excess  of  sulphuric  acid;  Decrease  of  the 
content  of  copper  in  the  bath;  Table  of  the  content  of  blue  vitriol  at 

different  degrees  of  Baume 565 

Electro-motive  force  in  the  cell-apparatus,  and  its  regulation;  Galvano- 
plastic deposition  by  the  battery  and  dynamo;  Arrangement  for  the 
employment  of  an  external  source  of  current       .....  566 

Regulation  of  the  current;  Deposition  with  the  battery;  Cells      .         .  567 
Deposition   with    the    dynamo;    Dynamos    suitable    for  the    purpose; 
Electro-motive  force  for  the  slow  process    ......  568 

Combination  of  dynamos  with  a  motor-generator  .....  569 

Coupling  the  baths;  Coupling  in  series 570 

Mixed  coupling  or  coupling  in  groups     .......  571 

Electro-motive  force  with  baths  coupled  in  parallel,  and  with  baths 
coupled  in  groups  ...........  572 

Combined  operation  with  dynamo  and  accumulators;  Disadvantage  of 
interrupting  the  galvanoplastic  deposition  of  copper  ....  573 

Copper  bath  for  galvanoplastic  deposition  with  a  separate  source  of 
current;  Functions  of  the  sulphuric  acid      ......  574 

Bath  for  the  reproduction  of  shallow  as  well  as  of  deep  moulds;  Prop- 
erties of   the  deposited  copper;    Bath   for  copper  printing  plates; 
Influence  of  the  temperature  of  the  electrolyte  on  the  mechanical 
properties  of  the  copper         .........  575 

Current  conditions;  Color  of  the  deposit  as  a  criterion  of  the  quality   .  576 

Table  showing  the  results  of  Hiibl' s  experiments 577 

Causes  of  brittle  copper  deposits;  Forster's  and  Hiibl's  investigations.  578 
E.  Miiller  and  P.  Behntje's  investigations  on  the  effects  of  organic 
additions;  Duration  of  deposition.         .......  579 

Table  of  the  duration  of  deposition  for  electrotypes  0.18  millimeter 
thick  with  different  current-densities;  Nitrate  baths  ....  580 

Agitation  of  the  baths 581 


XXV111  CONTENTS. 

PAGE 

Sand's  experiments 582 

Stirring  contrivances;  Agitation  of  the  bath  by  blowing  in  air;  Agita- 
tion by  flux  and  reflux 583 

Arrangement  of  the  baths  for  this  purpose 584 

Necessity  of  keeping  agitated  baths  clean;  Filtering;  Maximowitschs' 

plan  for  agitating  the  baths  .         .       • 585 

Anodes;  Effect  of  impurities  in  the  anodes;  Anode  slime        .         .         .  586 
Forster's  experiments;  Tanks;  Rapid  galvanoplasty       ....  587 
Principles  upon  which  the  process  of  rapid  galvanoplasty  is  based         .  588 
Bath  for  shallow  impressions  of  autotypes,  wood-cuts,  etc.;   Heating 
the  bath;   Danger  of  the  crystallization  of  blue  vitriol;  Agitation  of 

the  bath 590 

Current-density  for  this  bath;  Knight's  process  of  coppering  matrices.  591 

Bath  for  deep  depressions;  Rudholzner's  process 592 

Quality    of    the    copper    deposit;    Treatment    of    rapid    galvanoplastic 

baths- 593 

Examination  of  the  acid  copper  baths;    Determination   of  free  acid; 
Volumetric  determination  of  the  content  of  copper     .         .         .         .  594 

Electrolytic  determination  of  the  copper.         ......  595 

Operations  in  galvanoplasty  for  graphic  purposes;  Preparation  of  the 

moulds  (matrices)  in  plastic  material 596 

Moulding  in  gutta-percha,  and  in  wax     .......  597 

Mixtures  for  moulding  in  wax.         .         . 598 

Wax-melting  kettles;  Preparing  the  wax  for  receiving  the  impression; 
Moulding  box         .       ~-r^      .........  599 

Modern  method  of  operation;  Presses;  The  toggle  press        .         .         .  600 
Hydraulic    press         .         .         .         .         .         .         .         .         .         .         .  601 

Metal  matrices 602 

Dr.  E.  Albert  on  the  rational  preparation  of  metal  matrices.         .         .  603 
Basis  for  the  solution  of  the  problem;  Explanation  of  the  process.         .  605 

Fischer's  process;  Kunze's  method .  609 

Further  manipulation  of  the  moulds;  Removal  of  inequalities  and  eleva- 
tions; Making  the  moulds  conductive;  Black-leading  the  moulds  and 
machines  for  this  purpose  .........  610 

Black-leading  by  the  wet  process     . 612 

Electrical  contact;  Trimming  and  wiring  gutta-percha  moulds;  Feelers; 

Preparation  of  gutta-percha  moulds  for  suspension  in  the  bath  .         .  613 
Process  for  black-leaded  wax  moulds;    Hook  for  suspension  in  the 
bath;  Preventing  the  copper  deposit  from  spreading;  Treatment  of 
very  deep  forms     ...........  614 

Suspending  the  moulds  in  the  bath;  Detaching  the  deposit  or  shell 
from  the  mould  .  .  .  .  .  .  .  .  .  .  .615 

Moulding  arid  melting  table  for  wax  moulds 616 

Backing  the  deposit  or  shell     .         .         . 617 

Finishing;  Saw  table         ..........  618 

Planing  or  shaving  machines 619 


CONTENTS.  XXIX 


Copper  deposits  from  metallic  surfaces;  Process  of  making  a  copy 
directly  from  a  metallic  surface  without  the  interposition  of  wax  or 

gutta-percha 620 

Coppering  stereotypes       .         .         .         .         .         .         .         .         .         .  622 

Coppering  zinc  plates;    Preparation  of  type   matrices;   Treatment  of 

originals  of  hard  lead  or  similar  alloys;  Electro-etching     .         .         .  623 
Covering  or  etching  ground;  Work  of  the  engraver      ....  624 

Photo-engraving  and  processes  used 625 

Photo-galvanography 626 

Collographic  printing;  Zincography         .......  627 

Process  of  transferring  by  reprinting       .......  628 

Etching  with  the  assistance  of  the  electric  current         .         .         .         .  629 

Heliography 630 

Electro-engraving;  Rieder's  patented  process 631 

Apparatus  for*'  electro-engraving       ........  632 

Galvanoplastic  reproduction  of  plastic  objects;  Reproduction  of  busts, 

vases,  etc.;  Materials  for  the  moulds 634 

Moulding  surfaces  in  relief  and  not  undercut;  Dissection  of  the  ob- 
jects; Moulding  with  oil  gutta-percha 635 

Preparation  of  oil  gutta-percha;  Moulding  with  gutta-percha;  Metallic 

moulds,  and  metallic  alloys  for  this  purpose 636 

Plaster  of  Paris  moulds  and  their  preparation.         .....  637 

Moulding  large  objects 638 

Rendering  plaster-of-Paris  moulds  impervious        .....  639 
Metallizing  or  rendering  the  moulds  conductive;  Metallization  by  the 
dry  way^;  Metallization  by  metallic  powders         .....  640 

Metallization  by  the  wet  way 641 

Parkes'  method  of  metallization       ........  642 

Lenoir's  process— Galvanoplastic  method  for  originals  in  high  relief    .  643 
Gelatine  moulds,  and  directions  for  making  them.         ....  644 

Special  applications  of  galvanoplasty;  Nature  printing  .         .         .         .  645 

Production  of  copper  tubes;  Corvin's  niello    ......  646 

Plates  for  the  productions  of  imitations  of  leather;  Incrusting  galvano- 
plasty     .............  647 

Rendering  the  objects  impervious   ........  648 

Copper  bath  and  current  conditions;  Neubeck's  investigations  of  the 
work  in  the  cell-apparatus;  Additional  manipulation  of  the  deposits; 
Philip's  process  of  coating  laces  and  tissues  with  copper    .         .         .  649 
Coating  grasses,  leaves,  flowers,  etc.,  with  copper;  Providing  wooden 
handles  of  surgical  instruments  with  a  galvanoplastic  deposit  of  cop- 
per; Coppering  busts  and  other  objects  of  terra-cotta,  stoneware, 
clay,  etc.         ............  650 

Protecting  mercury  vessels  of  thermometers  by  a  galvanoplastic  de- 
posit of  copper;  Coppering  mirrors;  Galvanoplastic  decorations  on 
glass  and  porcelain  ware  .........  651 


XXX  CONTENTS. 

PAGE 

A.  A.  LeFort's  process  for  silver  deposit  on  glass  and  china;  Prepara- 
tion of  metallized  silver  .........  652 

Grinding  the  paint 653 

Firing  the  objects     .         .         .         .         .  .         .         .         .         .  654 

Plating  the  objects,  and  bath  for  this  purpose        .         .         .         .         .  655 

Decorating  umbrella  and  cane  handles  of  celluloid  with  a  metallic  de- 
posit; Coppering  baby  shoes,  carbon  pins  and  carbon  blocks,  rolls  of 
steel  and  cast  iron,  pump  pistons,  etc.,  steel  gun  barrels,  candela- 
bra, stairs,  and  structural  parts  of  buildings  of  rough  castings  .  .  656 

II.    GALVANOPLASTY  IN  IRON   (STEEL). 

First  production  of  serviceable  iron  electrotypes;  Klein's  bath  .  .  657 
Lenz's  investigations;  Dr.  George  Langbein's  investigations  .  %  658 
Precautionary  measures  to  counteract  the  spoiling  of  the  deposits; 

Contrivance  for  mechanically  interrupting  the  current  .  %  .  .  659 
Neubeck's  experiments;  Properties  of  electrolytically  deposited  iron; 

Advantages  of  steeled  copper  electrotypes 660 

III.    GALVANOPLASTY  IN  NICKEL. 

Production  of  nickel  electrotypes  in  an  indirect  way  ....  661 
Cold  nickel  bath  for  the  direct  method;  Requirements  for  working  with 

the  direct  process  of  deposition 662 

Most  suitable  electro-motive  force;  Devices  for  preventing  the  nickel 

deposit  from  rolling  off.  .........  663 

Nickel  matrices  .  .__  .  664 

Mode  of  effecting  an  intimate  union  of  the  copper  casing  with  the 

nickel *  .  665 

Matrices  of  massive  nickel  and  cobalt 666 

IV.    GALVANOPLASTY  IN    SILVER  AND  GOLD. 

Difficulties    in    the   preparation  of   reproduction    in    silver  and  gold; 

Moulding  of  the  originals .  667 

Baths  for  galvanoplasty  in  silver,  and  in  gold.         ,        .         .        .         .  668 

CHAPTER  XVIII. 
CHEMICALS  USED  IN  ELECTRO-PLATING  AND  GALVANOPLASTY. 

I.    ACIDS. 

Sulphuric  acid  (oil  of  vitriol)    .         .        .        .        .  -      .         .         .         .  669 

Recognition  of  sulphuric  acid;  Nitric  acid  (aqua  fortis,  spirit  of  nitre) 
and  its  recognition;  Hydrochloric  acid  (muriatic  acid)  and  its  recog- 
nition; Hydrocyanic  acid  (prussic  acid)  .  .  .  ..  .  .670 

Recognition  of  hydrocyanic  acid;  Citric  acid  and  its  recognition;  Boric 
acid  (boracic  acid)  and  its  recognition.  ....  :*.  .  671 

Arsenious  acid  (white  arsenic,  arsenic,  ratsbane)  and  its  recognition; 
Chromic  acid  and  its  recognition;  Hydrofluoric  acid  .  .  .  .  672 

Recognition  of  hydrofluoric  acid 673 


CONTENTS.  XXXI 


II.   ALKALIES  AND  ALKALINE  EARTHS. 

Potassium  hydrate  (caustic  potash);  Sodium  hydrate  (caustic  soda); 

Ammonium  hydrate  (ammonia  or  spirits  of  hartshorn)       .         .         .  673 
Recognition  of  ammonium   hydrate;  Calcium  hydrate  (burnt  or  quick 

lime) 674 

III.  SULPHUR  COMBINATIONS. 

Sulphuretted  hydrogen  (sulphydric  acid,  hydrosulphuric  acid)  and  its 
recognition;  Potassium  sulphide  (liver  of  sulphur)  ....  674 

Recognition  of  potassium  sulphide;  Ammonium  sulphide  (sulphydrate 
or  hydrosulphate  of  ammonium) ;  Carbon  disulphide  or  bisulphide; 
Antimony  sulphide;  Black  sulphide  of  antimony  (stibium  sulfuratum 
nigrum}',  Red  sulphide  of  antimony  (stibium  sulfuratum  aurantia- 
cum) ;  Arsenic  trisulphide  or  arsenious  sulphide  (orpiment)  .  .  675 

Ferric  sulphide 676 

IV.  CHLORINE  COMBINATIONS. 

Sodium  chloride  (common  salt,  rock  salt)  and  its  recognition;  Am- 
monium chloride  (sal  ammoniac)  and  its  recognition;  Antimony 
trichloride  (butter  of  antimony)  ........  676 

Arsenious  chloride;  Copper  chloride;  Tin  chloride — a.  Stannous  chlo- 
ride or  tin  salt  and  its  recognition,  b.  Stannous  chloride;  Zinc  chlo- 
ride (hydrochlorate  or  muriate  of  zinc) ;  Butter  of  zinc,  and  its  recog- 
nition   677 

Chloride  of  zinc  and  ammonia;  Nickel  chloride  and  its  recognition; 
Cobaltous  chloride  and  its  recognition;  Silver  chloride  .  .  .  678 

Recognition  of  silver  chloride;  Gold  chloride  (terchloride  of  gold, 
auric  chloride)  and  its  recognition;  Platinic  chloride  and  its  recog- 
nition   679 

v.  CYANIDES. 

Potassium  cyanide  (white  prussiate  of  potash) 680 

Comparative  table  of  potassium  cyanide  with  different  content;  Copper 

cyanide  and  its  recognition 682 

Zinc  cyanide  (hydrocyanate  of  zinc,  prussiate  of  zinc) ;  Silver  cyanide 
(prussiate  or  hydrocyanate  of  silver) ;  Potassium  ferrocyanide  (yellow 
prussiate  of  potash),  and  their  recognition 683 

VI.    CARBONATES. 

Potassium  carbonate  (potash)  and  its  recognition;  Acid  potassium 
carbonate,  commonly  called  bicarbonate  of  potash;  Sodium  car- 
bonate (washing  soda);  Sodium  bicarbonate  (baking  powder)  .  .  684 

Calcium  carbonate  (marble,  chalk);  Copper  carbonate,  zinc  carbonate, 
nickel  carbonate,  and  their  recognition  ......  685 

Cobaltous  carbonate  .  686 


XXX11  CONTENTS. 

PAGE 
VII.    SULPHATES  AND  SULPHITES. 

Sodium  sulphate  (Glauber's  salt);  Ammonium  sulphate,  potassium- 
aluminium  sulphate  (potash-alum),  and  their  recognition;  Alu- 
minium-alum ...........  686 

Recognition  of  aluminium-alum;  Ferrous  sulphate  (sulphate  of  iron, 
protosulphate  of  iron,  copperas,  green  vitriol),  and  its  recognition; 
Iron-ammonium  sulphate;  Copper  sulphate  (cupric  sulphate,  blue 
vitriol  or  blue  copperas) ,  and  its  recognition 687 

Zinc  sulphate  (white  vitriol),  nickel  sulphate,  and  their  recognition; 
Nickel-ammonium  sulphate 688 

Recognition  of  nickel-ammonium  sulphate;  Cobalt-ammonium  sul- 
phate; Sodium  sulphite  and  its  recognition;  Sodium  bisulphite  .  689 

Cuprous  sulphite        ...........  690 

VIII.    NITRATES. 

Potassium  nitrate  (saltpetre,  nitre),  and  its  recognition;  Sodium 
nitrate  (cubic  nitre  or  Chile  saltpetre);  Mercurous  nitrate.  .  .  690 

Mercuric  nitrate  (nitrate  of  mercury),  and  its  recognition;  Silver 
nitrate  (lunar  caustic) 691 

IX.  PHOSPHATES  AND  PYROPHOSPHATES. 

Sodium  phosphate,  sodium  pyrophosphate,  and  their  recognition; 
Ammonium  phosphate. 692 

X.    SALTS  OF  ORGANIC  ACIDS. 

Potassium  bitartrate  (cream  of  tartar) 692 

Potassium-sodium  tartrate  (Rochelle  or  Seignette  salt),  and  its  recog- 
nition; Antimony  potassium  tartrate  (tartar  emetic),  copper  acetate 
(verdigris)  and  their  recognition         .......  693 

Lead  acetate,  and  its  recognition;  Sodium  citrate 694 

APPENDIX. 

Contents  of  vessels;  To  find  the  number  of  gallons  a  tank  or  other 
vessel  will  hold;  Avoirdupois  weight;  Troy  weight  ....  695 

Imperial  fluid  measure;  Table  of  useful  numerical  data;  To  convert 
Fahrenheit  thermometer  degrees  (F.)  to  Centigrade  degrees  (C.); 
To  convert  Centigrade  degrees  to  Fahrenheit  degrees  .  .  .  696 

Table  for  the  conversion  of  certain  standard  weights  and  measures       .  697 

Table  of  solubilities  of  chemical  compounds  commonly  used  in  electro- 
technics 798 

Content  of  metal  in  most  commonly  used  metallic  salts.     .  .  .  700 

Table  showing  the  electrical  resistance  of  pure  copper  wire  of  various 
diameter;  Resistance  and  conductivity  of  pure  copper  at  different 
temperatures  .  .  .  .  .  .  .  ........  .  701 

Table  of  hydrometer  degrees  according  to  Baume,  at  63.5°  F.,  and 
their  weights  by  volume;  Table  of  bare  copper  wire  for  low  voltages.  702 

Index .'     ..         .703 


ELECTRO-DEPOSITION  OF  METALS. 


i. 

HISTORICAL  PART. 


CHAPTER  I. 

HISTORICAL    REVIEW    OF    ELECTRO-METALLURGY. 

IN  reviewing  the  history  of  the  development  of  electrolysis, 
'i.  e.,  the  reduction  of  a  metal  or  a  metallic  alloy  from  the 
solution  of  its  salts  by  the  electric  current,  the  simple  reduc- 
tion which  takes  place  by  the  immersion  of  one  metal  in  the 
solution  of  another,  may  be  omitted.  This  mode  of  reduction 
was  well  known  to  the  alchemist  Zozimus,  who  described  the 
reduction  of  copper  from  its  solutions  by  means  of  iron,  while 
Paracelsus  speaks  of  coating  copper  and  iron  with  silver  by 
simple  immersion  in  a  silver  solution.  • 

Before  the  discovery,  in  1789,  of  contact-electricity  by  Luigi 
Galvani,  there  was  nothing  like  a  scientific  reduction  of 
metals  by  electricity  ;  and  only  in  1799  did  Alexander  Volta, 
of  Pavia,  succeed  in  finding  the  true  causes  of  Galvani's  dis- 
covery. Galvani  observed,  while  dissecting  a  frog  on  a  table, 
whereon  stood  an  electric  machine,  that  the  limbs  suddenly 
became  convulsed  by  one  of  his  pupils  touching  the  crural 
nerve  with  the  dissecting-knife  at  the  instant  of  taking  a  spark 
from  the  conductor  of  the  machine.  The  experiment  was 
•several  times  repeated,  and  it  was  found  to  answer  in  all  cases 
when  a  metallic  conductor  was  connected  with  the  nerve,  but 
'not  otherwise.  He  observed  that  muscular  contractions  were 
1 


Z  ELECTRO-DEPOSITION    OF    METALS. 

produced  by  forming  a  connection  between  two  different 
metals,  one  of  which  was  applied  to  the  nerve,  and  the  other 
to  the  muscles  of  the  leg.  Similar  phenomena  having  been 
found  to  arise  when  the  leg  of  the  frog  was  connected  with 
the  electric  machine,  it  could  scarcely  be  doubted  that  in  both 
cases  the  muscular  contractions  were  produced  by  the  same 
agent.  From  a  course  of  experiments,  Galvani  drew  the 
erroneous  inference  that  these  muscular  contractions  were 
caused  by  a  fluid  having  its  seat  in  the  nerves,  which 
through  the  metallic  connections  flowed  over  upon  the  mus- 
cles. Everywhere,  in  Germany,  England  and  France,  emi- 
nent scientists  hastened  to  repeat  Galvani's  experiments,  in 
the  hope  of  discovering  in  the  organism  a  fluid  which  they 
considered  the  vital  principle  ;  but  it  was  reserved  to  Volta  to- 
throw  light  upon  the  prevailing  darkness.  In  his  repeated 
experiments  this  eminent  philosopher  observed  that  one  cir- 
cumstance had  been  entirely  overlooked,  namely,  that  in 
order  to  produce  strong  muscular  contractions  in  the  frog-leg 
experiment,  it  was  absolutely  necessary  for  the  metallic  con- 
nection to  consist  of  two  different  metals  coming  in  contact 
with  each  other.  From  this  he  drew  the  inference  that  the 
agent  producing  the  muscular  contractions  was  not  a  nerve- 
fluid,  but  was  developed  by  the  contact  of  dissimilar  metals, 
and  identical  with  the  electricity  of  the  electric  machine. 

This  discovery  led  to  the  construction  of  what  is  known  as 
the  pile  of  Volta,  or  the  voltaic  pile.  The  same  philosopher 
found  that  the  development  of  electricity  could  be  produced  by 
building  up  in  regular  order  a  pile  of  pairs  of  plates  of  dis- 
similar metals,  each  pair  being  separated  on  either  side  from 
the  adjacent  pairs  by  pieces  of  moistened  card-board  or  felt. 
On  account  of  various  defects  of  the  voltaic  pile,  Cruikshank 
soon  afterwards  devised  his  well-known  trough  battery,  which 
consisted  of  square  plates  of  copper  and  zinc  soldered  together,, 
and  so  arranged  and  fastened  in  parallel  order  in  a  wooden 
box  that  between  each  pair  of  plates  a  sort  of  trough  was- 
formed,  which  was  filled  with  acidulated  water. 


HISTORICAL    REVIEW    OF    ELECTRO-METALLURGY.  3 

Nicholson  and  Carlisle,  in  1800,  were  the  first  to  decompose 
water  electrolytically  into  hydrogen  and  oxygen,  using  a 
Volta  pile.  The  method  has  only  acquired  practical  im- 
portance during  the  last  few  years.  Wollaston,  in  1801,  found 
that  if  a  piece  of  silver  in  contact  with  a  more  positive  metal, 
for  instance,  zinc,  be  immersed  in  copper  solution,  the  silver 
will  be  coated  with  copper,  and  this  coating  will  stand 
burnishing. 

Cruikshank,  in  1803,  investigated  the  behavior  of  solutions 
of  nitrate  of  silver,  sulphate  of  copper,  acetate  of  lead,  and  of 
several  other  metallic  salts,  towards  the  galvanic  current,  and 
found  that  the  metals  were  so  completely  reduced  from  their 
solutions  by  the  current  as  to  suggest  to  him  the  analysis  of 
minerals  by  means  of  the  electric  current. 

To  Brugnatelli  we  owe  the  first  practical  results  in  electro- 
gilding.  In  1805,  he  gilded  two  silver  medals  by  connecting 
them  by  means  of  copper  wire  with  the  negative  pole  of  the 
pile,  and  allowing  them  to  dip  in  a  solution  of  fulminating 
gold  in  potassium  cyanide,  while  a  piece  of  metal  was  sus- 
pended in  the  solution  from  the  positive  pole.  He  also  ob- 
served that  the  positive  plate,  if  it  consisted  of  an  oxidizable 
metal,  was  dissolved. 

One  of  the  greatest  discoveries  connected  with  the  subject, 
however  is  that  of  Sir  Humphry  Davy,  in  1807,  when  by 
decomposing  potassium  hydroxide  and  sodium  hydroxide  by 
means  of  a  powerful  electric  current  he  obtained  the  metals 
potassium  and  sodium. 

Prof.  Oersted,  of  Copenhagen,  in  1820,  found  that  the  mag- 
netic needle  is  deflected  from  its  direction  by  the  electric 
current.  It  was  known  long  before  this  that  powerful  electric 
discharges  affect  the  magnetic  needle.  It  had,  for  instance, 
been  observed  that  the  needle  of  a  ship's  compass  struck  by 
lightning  had  lost  its  property  of  indicating  the  North  Pole, 
and  several  physicists,  among  them  Franklin,  had  succeeded 
in  producing  the  same  phenomena  by  heavy  discharges  of  the 
electrical  machine,  but  they  were  satisfied  with  the  supposition 


ELECTRO-DEPOSITION    OF   METALS. 

that  the  electric  current  acted  mechanically,  like  the  blow  of 
a  hammer.  Oersted  first  perceived  that  electricity  must  be  in 
a  state  of  motion  in  order  to  act  upon  magnetism.  This  led 
to  the  construction  of  the  galvanoscope  or  galvanometer,  an 
instrument  which  indicates  whether  the  cells  or  other  source 
of  current  furnish  a  current  or  not,  and  by  which  the  intensity 
of  the  source  of  current  may  also  to  a  certain  degree  be 
recognized. 

Ohm,  in  1827,  discovered  the  law  named  after  him,  that  the 
strength  of  a  continuous  current  is  directly  proportional  to  the 
difference  of  potential  or  electro-motive  force  in  the  circuit,  and 
inversely  proportional  to  the  resistance  of  the  circuit.  This  law 
will  be  more  fully  discussed  in  the  theoretical  part. 

Ohm's  discovery  was  succeeded,  in  1831,  by  the  important 
discovery  of  electric  induction  by  Faraday.  By  induction  is 
understood  the  production  of  an  electric  current  in  a  closed 
circuit  which  is  in  the  immediate  proximity  of  a  current- 
carrying  wire.  Faraday  further  found  that  the  current  in- 
duced in  the  contiguous  wire  is  not  constant,  because  after  a 
few  oscillations  the  magnetic  needle  returned  to  the  position 
occupied  by  it  before  a  current  was  passed  through  the  curre'nt- 
carrying  wire;  whilst,  when  the  current  was  broken,  the  needle 
deflected  in  the  opposite  direction. 

In  the  year  following  the  discovery  of  Faraday,  Pixii,  of 
Paris,  constructed  the  first  electro-magnetic  induction  machine. 

Faraday's  electrolytic  law  of  the  proportionality  of  the  cur- 
rent-strength and  its  chemical  action,  and  that  the  quantities 
of  the  various  substances  which  are  reduced  from/their  combi- 
nations by  the  same  current  are  proportional  to  their  chemical 
equivalents,  was  laid  down  and  proved  in  1833,  and  upon 
this  Faraday  based  the  measurements  of  the  current-strength 
by  chemical  deposition,  as,  for  instance,  that  of  water,  in  the 
voltmeter. 

Of  the  practical  electro-chemical  discoveries  there  remains 
to  be  mentioned  the  production  of  iridescent  colors,  in  1826, 
by  Nobili,  and  the  production  of  the  amalgams  of  potassium 
.and  sodium,  in  1853,  by  Bird. 


HISTORICAL    REVIEW    OF    ELECTRO-METALLURGY.  5 

The  actual  galvanoplastic  process,  however,  dates  from  1838. 
In  the  spring  of  that  year  Prof.  Jacob!  made  known  to  the 
Academy  of  Sciences  of  St.  Petersburg  his  discovery  of  the 
utility  of  galvanic  electricity  as  a  means  of  reproducing  objects 
of  metal.  He  produced  an  exact  mould  of  metals  and  artistic 
objects  by  means  of  wax  or  plaster,  and  then  coated  every 
detail  of  the  surface  of  this  mould  with  very  fine  graphite, 
thus  rendering  it  electrically  conductive.  He  then  suspended 
the  mould  from  the  negative  pole  (cathode)  of  an  electrolytic 
bath  containing  a  suitable  metallic  salt,  and  formed  the  posi- 
tive pole  of  the  same  metal ;  on  passing  an  electric  current 
through  this  bath  the  mould  became  lined  with  very  fine 
particles  of  metal,  forming  a  continuous  and  compact  surface. 
The  metal  forming  the  anode  was  gradually  dissolved  in  the 
bath  as  fast  as  it  was  deposited  on  the  cathode.  Hence, 
Jacobi  must  be  considered  the  father  of  galvanoplasty  in  so 
far  as  he  was  the  first  to  utilize  and  give  practical  form  to  the 
discoveries  made  up  to  that  time. 

Though  Jacobi's  process  was  published  in  the  English 
periodical,  "  The  Athenaeum."  of  May  4,  1839,  Mr.  T.  Spencer, 
who  read  a  paper  on  the  same  subject,  September  13,  1839, 
before  the  Liverpool  Polytechnic  Society,  claimed  priority  of 
invention,  as  was  also  done  by  Mr.  C.  J.  Jordan,  who,  on  May 
22,  1839,  sent  a  letter  to  the  "  London  Mechanical  Magazine," 
which  was  published  on  June  8,  1839. 

From  this  time  forward  the  galvanoplastic  art  made  rapid 
progress,  and  by  the  skill  and  enterprise  of  such  men  as  the 
Elkingtons,  of  Birmingham,  and  De  Ruolz,  of  Paris,  it  was 
speedily  added  to  the  industrial  arts. 

Though  copies  of  metallic  objects  by  means  of  galvanoplasty 
could  now  be  made,  the  employment  of  the  process  was  re- 
stricted to  metallic  objects  of  a  form  suitable  for  the  purpose, 
until,  in  1840,  Murray  succeeded  in  making  non-metallic  sur- 
faces conductive  by  the  application  of  graphite  (black  lead, 
plumbago),  which  rendered  the  production  of  galvanoplastic 
copies  of  wood-cuts,  plaster-of-Paris  casts,  etc.,  possible. 


6  ELECTRO-DEPOSITION    OF    METALS. 

Dr.  Montgomery,  in  1843,  sent  to  England  samples  of  gutta- 
percha,  which  was  soon  found  to  be  a  suitable  material  for  the 
production  of  negatives  of  the  original  models  to  be  reproduced 
by  galvanoplasty. 

Though  it  was  now  understood  how  to  produce  heavy  de- 
posits of  copper,  those  of  gold  and  silver  could  only  be  obtained 
in  very  thin  layers.  Scheele's  observations  on  the  solubility 
of  the  cyanide  combinations  of  gold  and  silver  in  potassium 
cyanide,  led  Wright,  a  co-worker  of  the  Elkingtons,  to  employ, 
in  1840,  such  solutions  for  the  deposition  of  gold  and  silver, 
and  it  was  found  that  deposits  produced  from  these  solutions 
could  be  developed  to  any  desired  thickness.  The  use  of 
solutions  of  metallic  cyanides  in  potassium  cyanide  prevails  at 
the  present  time,  and  the  results  obtained  thereby  have  not 
been  surpassed  by  any  other  practice. 

From  the  same  year  also  dates  the  patent  for  the  deposition 
of  nickel  from  solution  of  nitrate  of  nickel,  which,  however,  did 
not  attract  any  special  attention.  This  may  have  been  chiefly 
due  to  the  fact  that  the  deposition  of  nickel  from  its  nitrate 
solution  is  the  most  imperfect  and  the  least  suitable  for  the 
practice. 

To  Mr.  Alfred  Smee  we  owe  many  discoveries  in  the  deposi- 
tion of  antimony,  platinum,  gold,  silver,  iron,  lead,  copper,  and 
zinc.  In  publishing  his  experiments,  in  1841,  he  originated 
the  very  appropriate  term  "  electro-metallurgy  "  for  the  process 
of  working  in  metals  by  means  of  electrolysis. 

Prof.  Boettger,  in  1842,  pointed  out  that  dense  and  lustrous 
depositions  of  nickel  could  be  obtained  from  its  double  salt, 
sulphate  of  nickel  with  sulphate  of  ammonium,  as  well  as  from 
aminoniacal  solution  of  sulphate  of  nickel ;  and  that  such  de- 
posits, on  account  of  their  slight  oxidability,  great  hardness, 
and  elegant  appearance,  were  capable  of  many  applications. 
However,  Bcettger's  statements  fell  into  oblivion,  and  only  in 
later  years,  when  the  execution  of  nickeling  was  practically 
taken  up  in  the  United  States,  his  labors  in  this  department 
were  remembered  in  Germany.  To  Boettger  we  are  also  in- 


HISTORICAL    REVIEW    OF    ELECTRO-METALLURGY.  7 

•debied  for  directions  for  coating   metals  with  iron,  cobalt, 
platinum,  and  various  patinas. 

In  the  same  year,  De  Ruolz  first  succeeded  in  depositing 
metallic  alloys — for  instance,  brass — from  the  solutions  of  the 
mixed  metallic  salts.  In  1843,  the  first  use  of  thermo-electricity 
appears  to  have  been  made  by  Moses  Poole,  who  took  out  a 
patent  for  the  use  of  a  thermo-electric  pile  instead  of  a  voltaic 
battery  for  depositing  purposes. 

From  this  time  forward  innumerable  improvements  in  exist- 
ing processes  were  made  ;  and  also  the  first  endeavors  to  apply 
Faraday's  discoveries  to  practical  purposes. 

The  invention  of  depositing  metals  by  means  of  a  permanent 
•current  of  electricity  obtained  from  steel  magnets  was  perfected 
and  first  successfully  worked  by  Messrs.  Prime  &  Son,  at  their 
large  silverware  works,  Birmingham.  England,  and  the  original 
machine  constructed  by  Woolrych  in  1844 — the  first  magnetic 
machine  that  ever  deposited  silver  on  a  practical  scale — is 
still  preserved.  It  is  now  owned  by  the  Corporation  of  Birm- 
ingham, England.  The  Woolrych  machine  stands  5  feet  high, 
5  feet  long,  and  2J  feet  wide. 

As  early  as  1854,  Christofle  &  Co.  endeavored  to  replace 
their  batteries  by  magnetic-electrical  machines,  and  used  the 
Holmes  type,  better  known  as  the  Alliance  machine,  which, 
however,  did  not  prove  satisfactory;  and  besides,  the  prices  of 
these  machines  were,  in  comparison  with  their  efficiency,  exor- 
bitant. The  machine  constructed  by  Wilde  proved  objection- 
able on  account  of  its  heating  while  working,  and  the  conse- 
quent frequent  interruptions  in  the  operations. 

In  1860  Dr.  Antonie  Pacinotti,  of  Pisa,  suggested  the  use  of 
an  iron  ring  wound  around  with  insulated  wire,  in  place  of  the 
cylinder.  This  ring,  named  after  its  inventor,  has,  with  more 
or  less  modifications,  become  typical  of  many  machines  of 
modern  construction.  In  the  construction  of  all  older  ma- 
chines, steel  magnets  had  been  used,  and  their  magnetism  not 
being  constant,  the  effect  of  the  machine  was  consequently  also 
not  constant.  Furthermore,  they  generated  alternately  nega- 


0  ELECTRO-DEPOSITION    OF    METALS. 

live  and  positive  currents,  which,  by  means  of  commutators,, 
had  to  be  converted  into  currents  of  the  same  direction;  and 
this,  in  consequence  of  the  vigorous  formation  of  sparks, 
caused  the  rapid  wearing-out  of  the  commutators. 

These  defects  led  to  the  employment  of  continuous  mag- 
netism in  the  iron  cores  of  the  electro-magnets,  the  first 
machine  based  upon  this  principle  being  introduced  in  1866, 
by  Siemens,  which,  in  1867,  was  succeeded  by  Wheatstone's. 

However,  the  first  useful  machine  was  introduced  in  1871, 
by  Zenobe  Gramme,  who  in  its  construction  made  use  of  Paci- 
notti's  ring.  This  machine  was,  in  1872,  succeeded  by  Hefner- 
Alteneck's,  of  Berlin.  In  both  machines  the  poles  of  the 
electro-magnet  exert  an  inducing  action  only  upon  the  outer 
wire  wrappings  of  the  revolving  ring,  the  other  portions  being 
scarcely  utilized,  which  increases  the  resistance  and  causes  a 
useless  production  of  heat.  This  defect  led  to  the  construction 
of  flat-ring  machines,  in  which  the  cylindrical  ring  is  replaced 
by  one  of  a  flat  shape  and  of  a  larger  diameter,  thus  permitting 
the  induction  of  both  flat  sides.  Such  a  machine  was,  in  1874, 
built  by  Siemens  &  Halske,  of  Berlin;  and  in  the  same  year  by 
S.  Schuckert,  of  Nuremberg.  In  Schuckert's  machines  nearly 
three-quarters  of  all  the  wire  wrappings  were  under  the  induc-- 
ing  influence  of  both  of  the  large  pole  shoes  of  the  electro- 
magnets. The  flat-ring  armature  was  later  on  replaced  by  the 
drum  armature,  and  the  more  modern  machines  are  almost 
without  exception  of  the  drum-armature  type. 

By  the  construction  of  suitable  dynamo-machines  a  mighty 
impetus  was  given  to  the  electro-plating  industry.  They  sup- 
planted the  ordinary  cell  apparatus  formerly  used  and  ren- 
dered possible  the  production  of  electrolytically  nickeled,, 
coppered  and  brassed  sheet-steel  and  tin-plate,  as  well  as  that 
of  electrolytically  zincked  sheets,  wire,  building  materials,  etc. 
All  these  processes  will  be  fully  discussed  in  the  practical  part 
of  this  work. 


II. 

THEORETICAL  PART. 


CHAPTER  II. 

MAGNETISM    AND    ELECTRICITY. 

Magnetism. 

FOR  the  better  understanding  of  the  electrolytic  laws  it  will1 
be  necessary  to  commence  with  the  phenomena  presented  by 
magnetism,  and  to  consider  them  somewhat  more  closely. 

A  particular  species  of  iron  ore  is  remarkable  for  its  prop- 
erty of  attracting  small  pieces  of  iron  and  causing  them  to 
adhere  to  its  surface.  This  iron  ore  is  a  combination  of  ferric 
oxide  with  ferrous  oxide  (Fe304),  and  is  called  loadstone  or 
magnetic  iron  ore.  Its  properties  were  known  to  the  ancients, 
who  called  it  magnesian  stone,  after  Magnesia,  a  city  in  Thes- 
saly,  in  the  neighborhood  of  which  it  was  found.  In  the 
tenth  or  twelfth  century  it  was  discovered  that  this  stone  has 
the  property  of  pointing  north  and  south  when  suspended  by 
a  thread.  This  property  was  turned  to  advantage  in  naviga- 
tion and  the  term  load  stone  ("  leading  stone  ")  was  applied 
to  the  magnesian  stone.  If  a  natural  loadstone  be  rubbed 
over  a  bar  of  steel,  its  characteristic  properties  will  be  com- 
municated to  the  bar,  which  will  then  be  found  to  attract  iron 
filings  like  the  loadstone  itself.  The  bar  of  steel  thus  treated 
is  said  to  be  magnetized,  or  to  constitute  an  artificial  magnet. 
The  artificial  magnets  thus  produced  may  be  straight,  in  the 
shape  of  a  horse-shoe,  or  annular ;  but  no  matter  what  their 
form  may  be,  there  will  always  be  two  regions  where  the 

(9) 


10  ELECTRO-DEPOSITION    OF    METALS. 

attractive  force  reaches  its  maximum,  while  between  these 
two  points  there  is  a  region  which  has  no  attractive  effect 
whatever  upon  iron  filings.  The  two  ends  of  the  magnet, 
especially,  show  the  greatest  attractive  force,  and  they  are 
called  the  magnetic  poles,  whilst  the  line  running  around  the 
magnet,  which  possesses  no  attractive  force,  is  termed  the 
neutral  line  or  neutral  zone.  In  a  closed  magnet  the  poles  are 
situated  on  the  ends  of  one  and  the  same  diameter,  while  the 
neutral  zones  are  located  on  the  ends  of  a  diameter  standing 
perpendicular  to  the  first. 

When  a  magnetized  bar  or  natural  magnet  is  suspended  at 
its  center  in  any  convenient  manner,  so  as  to  be  free  to  move 
in  a  horizontal  plane,  it  is  always  found  to  assume  a  particular 
direction  with  regard  to  the  earth,  one  end  pointing  nearly 
north  and  the  other  nearly  south.  If  the  bar  be  removed  from 
this  position  it  will  tend  to  reassume  it,  and  after  a  few  oscilla- 
tions, settle  at  rest  as  before.  The  direction  of  the  magnetic 
bar,  i.  e.t  that  of  its  longitudinal  axis,  is  called  the  magnetic 
meridian,  while  the  pole  pointing  toward  the  north  is  usually 
distinguished  as  the  north  pole  of  the  bar,  and  that  which 
points  southward  as  the  south  pole. 

A  magnet,  either  natural  or  artificial,  of  symmetrical  form, 
suspended  in  the  presence  of  a  second  magnet,  serves  to  ex- 
hibit certain  phenomena  of  attraction  and  repulsion,  which 
deserve  particular  attention.  When  a  north  pole  is  presented 
to  a  south  pole,  or  a  south  pole  to  a  north  pole,  attraction  en- 
sues between  them,  the  ends  of  the  bar  approaching  each 
-other,  and,  if  permitted,  adhering  with  considerable  force. 
^VVhen,  on  the  other  hand,  a  north  pole  is  brought  near  a  sec- 
ond north  pole,  or  a  south  pole  near  another  south  pole, 
mutual  repulsion  is  observed,  and  the  ends  of  the  bar  recede 
from  each  other  as  far  as  possible.  Poles  of  an  opposite  name 
attract,  and  poles  of  a  similar  name  repel  each  other. 

According  to  Ampere's  theory,  each  molecule  of  iron  or 
steel  has  a  current  of  electricity  circulating  round  it ;  previous 
to  magnetization  these  molecules — and  hence  the  currents— 


MAGNETISM    AND    ELECTRICITY.  11 

:are  arranged  irregularly  ;  during  magnetization  they  are 
made  to  move  parallel  to  one  another,  and  as  the  magnetiza- 
tion becomes  more  perfect  they  gradually  assume  greater 
parallelism. 

If  an  iron  or  steel  needle  be  suspended  free  in  proximity  to 
a  magnet  it  assumes  a  fixed  direction  according  to  its  greater 
or  smaller  distance  from  the  poles  or  from  the  neutral  zone. 
However,  before  the  needle  assumes  this  direction,  it  swings 
rapidly  with  a  shorter  stroke,  or  slowly  with  a  longer  stroke, 
according  to  the  greater  or  smaller  attractive  force  exerted 
upon  it.  The  space  within  which  the  magnetic  action  of  a 
magnet  is  exercised  is  called  the  magnetic  field,  and  the  mag- 
netic, as  well  as  the  electric,  attractions  and  repulsions  are, 
according  to  Coulomb,  as  the  densities  of  the  fluids  acting  upon 
each  other,  and  inversely  as  the  square  of  their  distance. 

As  electro-magnets  act  in  exactly  the  same  manner  as  mag- 
nets, their  further  properties  will  be  discussed  in  the  next 
section.  , 

Electro-Magnetism. 

When  a  wire  through  which  a  current  is  passing  is  brought 
near,  and  parallel,  to  a  magnetic  needle,  the  latter  is  deflected 
from  its  ordinary  position,  no  matter  whether  the  current- 
carrying  wire  be  placed  alongside,  above,  or  beneath  it.  The 
deflection  of  the  needle  is  always  in  the  same  direction,  i.  e., 
its  north  pole  is  always  deflected  in  one  and  the  same  direction. 

The  direction  of  the  deflection  is  'determined  by  what  is 
known  as  Ampere's  rule,  which  i*  as  follows  :  Suppose  an  ob- 
server swimming  in  the  direction  of  the  current,  so  that  it 
enters  by  his  feet  and  emerges  by  his  head  :  if  the  observer 
has  his  face  turned  towards  the  needle,  the  north  pole  is  always 
deflected  to  his  left. 

When  the  current-carrying  wire  is  coiled  in  many  windings 
around  the  needle,  the  action  of  the  current  is  increased,  be- 
cause every  separate  winding  deflects  the  north  pole  in  the 
same  direction.  Such  instruments  are  known^as  multipliers,  or 


12  ELECTRO-DEPOSITION    OF    METALS. 

galvanoscopes,  or  galvanometers,  and  are  used  for  recognizing 
feeble  currents.  These  instruments  have  been  improved  by 
Nobili  through  the  use  of  a  very  long  coil  of  wire,  and  by  the 
addition  of  a  second  needle.  This  instrument  is  known  as  the 
astatic  galvanometer.  The  two  needles  are  of  equal  size  andi 
magnetized  as  nearly  as  possible  to  the  same  extent.  They 
are  then  immovably  fixed  together  parallel  and  with  their 
poles  opposed,  and  hung  by  a  long  fiber  of  twisted  silk,  with 
the  lower  needle  in  the  coil  and  the  upper  one  above  it.  The 
advantage  thus  gained  is  twofold :  The  system  is  astatic,  un- 
affected, or  nearly  so,  by  the  magnetism  of  the  earth  ;  and  the 
needles  being  both  acted  upon  in  the  same  manner  by  the 
current,  are  urged  with  much  greater  force  than  one  alone 
would  be,  all  the  actions  of  every  part  of  the  coil  being  strictly 
concurrent.  A  divided  circle  is  placed  below  the  upper  needle, 
by  which  the  angular  motion  can  be  measured,  and  the  whole 
is  inclosed  in  glass,  to  shield  the  needles  from  the  agitation  of 
the  air. 

The  deflection  of  the  magnetic  needle  by  the  electric  current 
has  led  to  the  construction  of  instruments  which  allow  of  the 
intensity  of  the  current  being  measured  by  the  magnitude  of 
the  deflection.  Such  instruments  are,  for  instance,  the  tangent 
galvanometer,  the  sine  galvanometer,  etc.,  but  they  are  almost 
exclusively  used  for  scientific  measurements,  while  for  the  de- 
termination of  the  intensity  of  current  for  electro-plating  pur- 
poses other  instruments  are  employed,  which  will  be  described 
later  on.  However,  the  electric  current  exerts  not  only  a  re- 
flecting action  on  magnetic  fteedles,  but  is  also,  capable  of  pro- 
ducing a  magnetizing  effect  on  iron  and  steel.  If  a  bar  of  iron 
be  surrounded  by  a  coil  of  wire  covered  with  silk  or  cotton  for 
the  purpose  of  insulation,  it  becomes  magnetic  so  long  as  the 
current  is  conducted  through  the  coil.  Such  iron  bars  con- 
verted into  temporary  magnets  by  the  action  of  the  current 
are  called  electro-magnets,  and  they  will  be  the  more  highly 
magnetic,  the  greater  the  number  of  turns  of  the  coil,  and  the 
more  intense  the  current  passing  through  the  turns.. 


MAGNETISM    AND    ELECTRICITY. 


13 


The  magnitude  of  the  magnetizing  force  of  the  current  is 
-expressed  by  the  product  from  the  number  of  turns  and  cur- 
rent-strength passing  through  the  turns,  and  is  called  ampere- 
turn  number. 

By  interrupting  the  current  passing  through  the  wire-turns, 
the  magnetism  of  the  iron  bar  disappears  to  within  a  very 
small  quantity,  its  magnitude  depending  on  the  quality  of  the 
iron.  This  remaining  magnetism  is  called  remanent  or  residual 
magnetism. 

An  electro-magnet  possesses  the  same  properties  as  an  ordi- 
nary magnet,  and,  like  it,  has  a  north  pole  and  a  south  pole, 

FIG.  1. 


-as  well  as  a  magnetic  field,  through  which  its  influence  ex- 
tends. Place  a  piece  of  paper  above  an  electro-magnet  and  sift 
uniformly  iron  filings  over  it.  On  giving  the  paper  slight 
taps,  the  filings  arrange  themselves  in  regular  groups  and 
lines.  Most  of  the  filings  collect  on  the  two  poles,  while,  in 
fixed  decreasing  proportions,  lines  of  filings  are  formed  from 
the  north  pole  to  the  south  pole.  This  experiment  demon- 
strates that  the  action  is  strongest  on  the  poles,  and  decreases 
towards  the  center.  The  entire  space  in  which  the  magnetic 
action — the  flow  of  the  magnetic  lines  of  force — exerts  its  influ- 
ence is  called  the  magnetic  field.  The  lines  of  force  flow  from 
the  north  pole  to  the  south  pole,  where  they  combine,  and  flow 


14  ELECTRO-DEPOSITION    OF    METALS. 

back  through  the  iron  bar  to  the  north  pole,  as  shown  in  the- 
accompanying  illustration,  Fig.  1. 

The  dotted  lines  also  take  actually  their  course  from  one 
pole  to  the  other,  but  by  a  more  circuitous  way.  The  direc- 
tion, as  well  as  the  magnitude,  of  the  field  force  (see  later  on) 
varies  on  all  points  of  the  magnet  or  electro-magnet,  with  the 
sole  exception  of  the  symmetrical  plane  between  the  two  poles, 
the  latter  being  on  all  points  struck  at  right  angle  by  the  lines 
of  force. 

By  placing  a  bar  of  soft  iron,  a  b,  in  the  proximity  of  a  mag- 

FIG.  2. 

\       '       f       '  \      ^  i 

^  \  -.  '  /^.-j^xY,  /  /  ' 


i  *  ^  ^-  —  —  —  „  ^  ^  ^  *          ,     / 
v  '  /  *,'.;*  ^  -  -~^^^\  \  /   /    /   / 

x  ^  \  i'///;^--'----- ^3^\i  i  '   '  / 

x    f '  iff/^  --  "^_  ~  -~^~  ^^  ^ }  1 1   '  /     s         / 
>^kLJ£raS^£^sS&S^^£bi£^X''     <"        s 


net  or  electro-magnet  N  S,  covering  both  with  a  sheet  of  paper 
and  sifting  iron  filings  upon  the  latter,  delineations,  as  shown 
in  Fig.  2,  are  obtained. 

The  lines  of  force  gravitate  in  large  numbers  towards  the 
side  where  the  iron  bar  is,  traverse  the  iron  quite  compactly, 
and  while,  without  the  bar,  the  center  of  the  magnet  showed  a 
feeble  magnetic  field,  the  field-force  in  that  place  has  now 
become  greater.  Upon  the  opposite  side  the  density  of  the 
lines  of  force  which  pass  through  the  air  is  less.  The  prop- 
erty of  a  material  to  be  traversed  by  the  lines  of  force  is  called 
its  permeability. 

The  number  of  lines  of  force  which  traverses  through  1 


MAGNETISM    AND    ELECTRICITY.  15- 

square  centimeter  of  cross-section  of  a  material,  is  called  the 
magnitude  of  the  magnetic  induction  of  the  material  in  question. 

Every  material  opposes  a  certain  fixed  resistance  to  the 
electrical  current,  as  well  as  to  the  magnetic  lines  of  force. 
Soft  iron  opposing  the  least  resistance  to  the  lines  of  force,  it 
is  most  compactly  traversed  by  them.  Air,  on  the  'other 
hand,  opposes  far  greater  resistance,  and,  hence,  the  density  of 
the  lines  of  force,  in  Fig.  2,  where  they  pass  through  the  air 
is  much  less. 

A  conducting  wire  through  which  passes  a  powerful  current 
also  becomes  itself  magnetic.  If  a  circular  conducting  wire, 
through  which  a  current  passes,  be  suspended  so  as  to  move 
free  around  its  vertical  axis,  its  direction  is  influenced  by  the 
terrestrial  magnetism,  and  it  assumes  such  a  position  that  its 
plane  stands  at  a  right  angle  upon  the  plane  of  the  magnetic 
meridian.  By  now  conducting  the  current  through  a  spiral 
wire  suspended  free — a  so-called  solenoid — the  plane  of  eacrr 
separate  turn  will  also  place  itself  at  a  right  angle  upon  the 
plane  of  the  magnetic  meridian,  or  in  other  words,  the  axis  of 
the  solenoid  will  be  brought  to  lie  in  the  magnetic  meridian. 

In  a  manner  similar  to  the  action  upon  a  magnet  by  a  con- 
ducting wire  through  which  a  current  passes,  two  conducting 
wires,  through  which  currents  pass,  exert  attracting  and  re- 
pelling influences  one  upon  the  other.  Two  currents  running 
parallel  alongside  each  other  in  the  same  direction  attract,, 
but  repel,  each  other,  when  running  in  opposite  directions. 

Induction. 

By  induction  is  understood  the  production  of  an  electric 
current  in  a  closed  conductor  which  is  in  the  immediate 
proximity  of  a  current-carrying  wire. 

Suppose  we  have  two  insulated  copper-wire  coils,  a  and  b, 
Fig.  3,  b  being  of  a  smaller  diameter  and  inserted  in  a. 
When  the  two  ends  of  b  are  connected  with  the  poles  of  a 
battery,  a  current  is  formed  in  a  the  moment  the  current  of 
6  is  closed.  This  current  is  recorded  by  the  deflection  of  the 


16 


ELECTRO-DEPOSITION    OF    METALS. 


magnetic  needle  of  a  multiplier,  M,  which  is  connected  with 
the  ends  of  a,  the  deflection  of  the  needle  showing  that  the 
current  produced  in  a  by  the  current  in  b  moves  in  an  oppo- 
site direction.  The  current  in  a,  however,  is  not  lasting, 
because,  after  a  few  oscillations,  the  magnetic  needle  of  the 
multiplier  returns  to  its  previous  position  and  remains  there, 
no  matter  how  long  the  current  may  pass  through  b.  If, 
however,  the  current  in  b  be  interrupted,  the  magnetic  needle 
swings  to  the  opposite  direction,  thus  indicating  the  formation 


FIG.  3. 


of  a  current  in  a,  which  passes  through  it  in  the  same  direc- 
tion as  the  interrupted  current  in  b. 

The  current  causing  this  phenomenon  is  called  the  primary, 
inducing  or  main  current,  and  that  produced  by  it  in  the 
closed  circuit,  the  secondary,  induced  or  induction-current.  From 
what  has  been  above  said,  it  is  clear  that  an  electric  current  at 
the  moment  of  its  formation  induces  in  a  contiguous  closed  circuit 
a  current  of  opposite  direction,  but  when  interrupted,  a  current  of 
the  same  direction. 

In  the  same  manner  as  closing  and  opening  the  main  cur- 


MAGNETISM    AND    ELECTRICITY.  17 

rent,  its  sudden  augmentation  also  effects  the  induction  of  a 
current  of  opposite  direction  in  a  contiguous  wire,  while  its 
sudden  weakening  induces  a  current  of  the  same  direction. 
The  same  effect  is  also  produced  by  bringing  the  main  current- 
carrying  wire  closer  to,  or  removing  it  further  from,  the  con- 
tiguous wire. 

It  is  supposed  that  by  closing  the  current  a  magnetic  field  is 
formed  in  the  coil  b,  which  sends  forth  its  lines  of  force  radially 
in  an  undulating  motion.  The  lines  of  force  cut  the  turns  of 
the  coil,  a,  which  is  without  current,  and  thereby  induces  a 
current.  This  current  disappears  again  when  the  primary 
current  flows  in  equal  force,  and  re-appears  when  by  the 
strengthening  of  the  inducing  current  a  change  in  the  number 
of  lines  of  force  takes  place  by  reason  of  the  strengthening  of 
the  magnetic  field.  In  the  same  manner  induced  currents  are 
also  produced  by  a  decrease  in  the  number  of  lines  of  force, 
and  hence  it  follows  that  the  production  of  induction-currents 
is  always  conditional  on  the  change  of  proportion  between  the 
conductor  and  the  magnetic  field. 

When  a  magnet  or  electro-magnet  is  pushed  into  a  wire  coil, 
an  electric  current  is  produced  in  the  turns  of  the  coil  so  long 
as  the  motion  of  the  magnet  is  continued;  when  the  motion  is 
interrupted,  the  production  of  current  ceases.  If  the  magnet 
be  now  withdrawn  from  the  coil,  a  current  is  again  formed, 
which,  however,  flows  in  an  opposite  direction  to  that  formed 
by  pushing  the  magnet  into  the  coil.  The  currents  produced 
in  the  above-mentioned  manner  are  also  induction-currents, 
and  their  formation  is  again  explained  by  the  fact  that  the 
lines  of  force  cut  the  turns  of  the  conducting  wire,  and  excite 
thereby  a  current,  the  electro-motive  force  of  which  increases 
or  decreases  with  the  magnitude  of  the  number  of  lines  of 
force. 

The  induced  currents  follow  the  law  of  Ohm  (see  later  on) 

in  precisely  the  same  manner  as  the  inducing  currents.     A 

long  induction-wire  with  a  small   cross-section  offers  greater 

resistance  than  a  short  wire  with  a  larger  cross-section,  and 

2 


18  ELECTRO-DEPOSITION    OF    METALS. 

consequently,  in  the  first  case,  the  current  will  be  of  slighter 
intensity  and  higher  electro-motive  force,  and,  in  the  other,  of 
greater  intensity  and  less  electro-motive  force. 

Electro-magnetic  alternating  actions  are  the  relations  which 
exist  between  the  magnetic  field,  the  conductor,  and  the 
motion.  The  direction  of  the  induced  current  can  readily  be 
followed  by  Fleming's  hand  rule,  which  is  as  follows :  Hold 
the  thumb  and  the  first  and  the  middle  fingers  of  the  right 
hand  as  nearly  as  possible  at  right  angles  to  each  other,  as 
shown  in  Fig.  4,  so  as  to  represent  three  rectangular  axes  in 
space.  If  the  thumb  points  in  the  direction  of  motion,  and 

FIG.  4. 


the  forefinger  points  along  the  direction  of  the  magnetic  lines, 
then  the  middle  finger  will  point  in  the  direction  of  the  in- 
duced electro-motive  force. 

The  mechanism  of  the  formation  of  the  electric  current  will 
be  fully  discussed  later  on,  but  it  will  be  necessary  to  here 
give  the  values  in  which  the  performances  of  the  current  are 
expressed  in  order  to  shape  the  succeeding  chapters  more  uni- 
formly. 

fundamental  Principles  of  Electro- Technics. 

Electric  Units.  For  the  better  comprehension  of  the  prop- 
erties, effects,  and  value  of  the  electric  current,  it  has  become- 


MAGNETISM    AND    ELECTRICITY. 


19 


customary  to  compare  it  with  a  current  of  water,  and  this  cus- 
tom will  here  be  followed. 

Fig.  5  shows  a  funnel  A  secured  in  the  stand  D,  and  con- 
nected by  a  tube  with  the  horizontal  discharge  pipe  B 
Underneath  B  stands  the  vessel  (7,  which  serves  for  catching 
the  water.  If  the  funnel  be  placed  in  a  higher  position  and 
filled  with  water,  the  latter  runs  off  more  rapidly  from  the 
pipe  B,  than  when  the  funnel  occupies  a  lower  position.  If 

Fig.  5. 


the  force  of  the  current  of  water  is  expressed  according  to  the 
quantity  of  water  which  runs  out  in  the  time-unit,  it  follows 
that  in  a  certain  pipe  conduit,  the  quantity  of  water  which 
runs  out  in  the  time-unit,  increases  if  there  be  an  increase  in 
the  height  of  fall. 

Suppose  it  has  been  determined  how  many  seconds  are  re- 
quired for  the  water  in  the  funnel  to  run  through  the  pipe  B. 
If  the  pipe  be  now  lengthened  by  joining  to  it  several  pipes  of 


20  ELECTRO-DEPOSITION    OP    METALS. 

the  same  cross-section,  it  will  be  found  that  a  greater  number 
of  seconds  are  required  for  emptying  the  funnel  than  with  the 
use  of  only  one  pipe.  From  this  we  learn  that  with  a  deter- 
mined height  of  fall,  the  quantity  of  water  which  flows  in  the 
time-unit  through  a  pipe  of  determined  cross-section  decreases 
when  the  pipe  is  lengthened. 

If  now  the  discharge  pipes  used  in  the  last  experiment  be 
replaced  by  pipes  of  the  same  length  but  of  smaller  cross- 
sections,  it  will  be  found  that  a  greater  number  of  seconds  are 
also  required  for  emptying  the  funnel  than  with  the  use  of 
pipes  of  larger  cross-sections.  Hence,  at  a  determined  height 
of  fall,  the  quantity  of  water  which  flows  through  a  pipe  of 
fixed  length  in  the  time-unit,  decreases  if  the  cross-section  of 
the  pipe  be  increased. 

The  height  of  fall  has  to  be  considered  as  the  motive  power 
which  effects  the  flow  of  water.  The  pipe  opposes  a  resistance 
to  the  flowing  water,  this  resistance  increasing  with  the  length 
of  the  pipe  and  the  reduction  of  the  cross-section,  and  decreas- 
ing as  the  cross-section  becomes  larger. 

If  now  these  principles  be  applied  to  the  electric  current,  by 
current-strength  has  to  be  understood  the  quantity  of  electricity 
which  passes  in  the  time-unit  through  a  conductor. 

The  unit  of  the  quantity  of  electricity  is  called  the  coulomb. 
Its  magnitude  results  from  the  fact  that  for  the  1  gramme 
hydrogen  96,540  coulombs  must  migrate  through  the  elec- 
trolyte. 

The  unit  of  current-strength  is  called  the  ampere,  i,  e.,  a  cur- 
rent which  every  second  carries  one  coulomb  through  the  con- 
ductor. The  magnitude  of  an  ampere  is  the  current-strength 
which  is  capable  of  separating  in  one  minute  0.01973  gramme 
of  copper,  or  in  one  hour  1.184  grammes,  from  a  cupric  sul- 
phate solution.  In  order  to  separate  from  an  electrolyte  1 
gramme  of  hydrogen,  a  current  of  1  ampere  must  accordingly 
pass  96,540  seconds,  or  26  hours  49  minutes,  through  the 
electrolyte. 

The  electro-motive  force  or  tension  of  the  electric  current  cor- 


MAGNETISM    AND    ELECTRICITY.  21 

responds  to  the  height  of  fall  of  water.  The  work  an  electric 
current  is  capable  of  performing  does  not  only  depend  on  the 
current-strength,  i.  e.,  the  quantity  of  current,  which  passes 
in  the  time-unit  through  a  cross-section  of  the  conductor,  hut 
also  on  the  electro-motive  force.  The  unit  of  electro-motive  force 
is  called  the  volt.  The  material  value  of  a  volt  is  about  the 
electro-motive  force  of  a  Daniell's  cell  (zinc-copper). 

In  a  water  conduit  the  difference  in  pressure  between  two 
points  in  the  pipe  is  measured  according  to  the  difference  in 
the  height  of  the  column  of  water.  To  this  difference  in  pres- 
sure corresponds  the  difference  of  electro-motive  force,  also  called 
difference  of  potential,  which  is  expressed  by  the  number  of 
volts. 

The  product  of  current-strength  in  amperes  and  electro- 
motive force  in  volts,  which,  in  so  far  as  an  ampere  is  an 
electric  unit  in  one  second,  represents  work  performed  in  one 
second,  is  called  the  volt-ampere  or  ivatt,  and  hence  is  the  unit 
of  electrical  work. 

The  electric  resistance  is  similar  to  the  resistance  offered  by 
a  water-pipe  to  the  flowing  water.  As  previously  stated,  the 
quantity  of  water  running  out  in  the  time-unit  decreases  when 
the  pipe  is  lengthened,  as  well  as  when  the  cross-section  is 
smaller,  and,  in  both  cases,  the  resistance  opposed  to  the  water 
by  friction  increases.  On  the  other  hand,  the  quantity  of 
water  flowing  out  in  the  time-unit  increases,  when  the  length 
of  pipe  is  shortened  and  the  cross-section  increased,  because 
there  is  less  resistance.  The  same  takes  place  with  the  electric 
current.  The  quantity  of  current  which  can  pass  through  a 
conductor  becomes  smaller  when  the  length  of  the  conductor 
is  increased  and  its  cross-section  reduced,  because  the  resist- 
ance becomes  thereby  correspondingly  greater.  It  has  further 
been  seen  that  the  quantity  of  flowing  water  in  a  certain  con- 
duit increases  as  the  height  of  fall  becomes  greater.  If  now 
the  electro-motive  force  of  the  electric  current  be  substituted 
for  the  height  of  fall,  the  current-strength  which  passes  through 
a  conductor  will  be  increased  in  keeping  with  the  changing 


22  ELECTRO-DEPOSITION    OF    METALS. 

electro-motive  force.  From  this  results  the  following  propo- 
sition : 

In  a  determined  circuit  the  current-strength  increases  at  the 
same  ratio  as  the  electro-motive  force  which  acts  upon  the  circuit. 

If  now  the  current-strength  increases  proportionally  to  the 
electro-motive  force,  the  expression, 

E(=  electro-motive  force  in  the  circuit) 
J '(=  current-strength  in  the  circuit), 

must  be  a  fixed  value  dependent  on  the  magnitude  of  the 
electro-motive  force  and  the  current-strength,  and  this  value  is 
called  the  electric  resistance  of  the  circuit. 

The  unit  of  electric  resistance  is  called  the  ohm,  it  having  thus 
been  named  after  the  physicist  Ohm,  who  laid  down  the  rules 
known  as  the  laws  of  Ohm.  The  value  of  the  ohm  is  equal  to 
the  resistance  at  0°  C.  of  a  column  of  mercury  of  one  square 
millimeter  section  and  one  meter  long.  A  volt  is  the  electro- 
motive force  which  is  capable  of  sending  a  current-strength  of 
one  ampere  through  the  resistance  of  one  ohm. 

Law  of  Ohm.     It  has  above  been  seen  that  the  fraction 

(1)  E  =  resistance  (W), 
<J 

whereby  under  E  is  understood  the  electro-motive  force  which 
is  at  disposal  in  the  entire  circuit.  The  current-strength  J  is 
throughout  in  all  places  of  the  same  magnitude,  and  IT7  indi- 
cates the  total  resistance  of  the  circuit. 

From  the  preceding  equation  are  deduced  the  following 
further  equations  : 

(2)  W.  J=E, 

that  is,  the  electro-motive  force  is  equal  to  the  product  of 
current-strength  and  resistance; 

^TV=J'      :      , 

that  is,  the  current-strength  is  equal  to  the  electro-motive 
force  divided  by  the  resistance. 

Example  to  equation  1.     If  through  a  circuit  closed  by  a  long 


MAGNETISM    AND    ELECTRICITY.  23 

wire  and  a  current-meter,  a  current  of  4  volts  and  2  amperes 
is  conducted,  the  resistance  of  the  circuit  is 

ivolte     .  ^  2  ohms. 
2  amperes 

Example  to  equation  2.  5  amperes  are  to  be  conducted 
through  a  circuit  of  1  ohm  resistance,  what  electro-motive 
force  is  required  for  the  purpose?  ^ 

1  ohm  X  5  amperes  =  \volt. 

Example  to  equation  3.  A  current  of  10  volts  electro-motive 
force  is  to  be  conducted  through  a  circuit  with  2  ohms  resist- 
ance ;  what  current-strength  may  be  looked  for? 

10volts  =  5  amperes.  . 
2   ohms 

The  total  resistance,  W,  is  composed  of  the  internal  resist- 
ance of  the  current-source  and  the  external  resistance  which  the 
current  in  its  progression  has  to  overcome.  This  external  re- 
sistance is  composed  of  the  resistance  of  the  conducting  wire, 
the  electrolyte,  etc.  If  the  internal  resistance  be  designated 
W  and  the  external  resistances  wl  and  w2,  equation  3  assumes 
the  following  aspect  : 

W  +  wl  +  w~2  =  J' 

Hence,  the  current-strength  is  equal  to  the  total  electro- 
motive force  divided  by  the  sum  of  the  internal  and  external 
resistances. 

Example  to  equation  4-  A  cell  possesses  an  internal  resist- 
ance of  0.3  ohm  and  an  electro-motive  force  of  1.8  volts,  and 
the  resistance  of  the  conducting  wire,  wl,  is  1  ohm  and  that 
of  the  electrolyte  0.5  ohm.  The  current-strength  then  amounts 

-i    o 

—  -  — 

o.3  +  1  +  0.5" 

If  a  determined  current-strength  flows  through  a  resistance, 
a  decrease  of  electro-motive  force  results  in  the  resistance,  ex- 
actly as  in  a  water-conduit  the  pressure  of  the  column  of  water 
is  decreased  with  the  length  of  the  pipe,  a  decrease  in  pressure 
taking  place.  It  might  be  said  that  the  resistance  consumes 


/  -i 

to  1  ampere  (  -  — 
Vo.3  +  1 


24  ELECTRO-DEPOSITION    OF    MET.ALS. 

the  pressure,  and  the  greater  the  resistance  of  a  conductor  is, 
the  less  the  current-strength  will  be,  since,  if  in  the  equation  3 
the  divisor  grows,  the  current-strength,  J,  must  become  less. 
According  to  the  law  of  Ohm,  the  following  proposition  here 
holds  good  : 

The  current-strength  is  inversely  proportional  to  the  sum  of  the 
resistance  of  the  circuit,  or,  in  other  words,  the  current-strength 
decreases  in  the  proportion  as,  with  the  same  electro-motive 
force,  the  resistances  increase. 

The  resistance  of  a  wire  or  of  a  body  increases  in  proportion 
to  its  increase  in  length,  and  decreases  in  proportion  to  the  in- 
crease of  its  cross-section.  If  the  resistance  of  a  conductor  be 
designated  W,  its  length  L,  and  its  cross-section  Q,  then 


The  decreasing  electro-motive  force,  according  to  the  law  of 
Ohm,  is  calculated  by  the  following  equation,  in  which  a 
denotes  the  decrease  in  electro-motive  force,  J  the  current- 
strength,  Wi  the  internal  resistance. 

(6)  a  =  J  X  Wi. 

In  the  example  to  equation  4,  the  current-strength  amounted 
to  1,  and  the  internal  resistance  of  the  element  to  0.3  ohm; 
this  gives  a  decrease  of  electro-motive  force  of  1  x  0.3  =  0.3 
volt;  hence  the  actual  electro-motive  force  of  the  current  flow- 
ing from  the  cell  will  only  be:  E  —  a  =  1.8  —  0.3  =  1.5  volts, 
and  this  effective  electro-motive  force  is  called  the  impressed 
electro-motive  force  of  the  cell  or  other  source  of  current. 

If  now  the  preceding  separate  propositions  of  the  law  of 
Ohm  be  collected,  the  latter  reads  as  follows: 

The  current-strength  is  directly  proportional  to  the  sum  of  the 
electro-motive  forces,  and  inversely  proportional  to  the  resistance 
of  the  circuit  ;  however,  the  resistance  of  each  part  of  the  circuit 
is  proportional  to  its  length,  and  inversely  proportional  to  its  cross- 
section. 

Specific  resistances.  The  resistance  of  a  wire  of  the  same 
material  is  consequently  proportional  to  its  length  and  in- 


MAGNETISM    AND    ELECTRICITY. 


25 


versely  proportional  to  its  cross-section.  If  now,  one  after  the 
other,  wires  of  equal  length  and  equal  cross-section,  but  of 
different  materials,  be  placed  between  the  binding  posts  of  a 
source  of  current,  different  current-strengths  are  obtained  in 
the  wires.  From  this  it  follows  that  every  material  possesses 
a  definite  capacity  of  its  own  to  conduct  the  current.  Hence, 
if  the  resistance  is  to  be  calculated  from  the  length  of  the  wire 
and  its  cross-section,  the  magnitude,  called  the  specific  resist- 
ance of  the  material,  has  to  be  taken  into  consideration.  By 
the  specific  resistance  is  to  be  understood  for  conductors  of 
the  first  class,  the  resistance  of  a  material  1  meter  in  length 
and  1  square  millimeter  cross-section,  and  for  conductors  of 
the  second  class,  the  resistance  of  a  cube  of  fluid  of  10  centi- 
meters =  1  decimeter  side  length. 

If  the  specific  resistance  be  denoted  c,  the  resistance  of  a 
wire  of  L  meters  length  and  a  cross-section  of  Q  square  milli- 
meters cross-section  is  found  from  the  equation  : 

(7)  W  =  L.  c. 

The  specific  resistance  c  of  the  metals  at  59°  F..  and  the  co- 
efficient of  temperature  a  (see  later  on)  amount  to  for : 


Aluminium  .  .  , 
Antimony .... 
Bismuth  .  .  .  . 

Brass 

Copper  

German  silver  .  . 

Gold 

Iron 

Lead 

Manganin  .... 
Mercury  .  .  .  . 

Nickel 

Xickelin  .... 
Platinum  .... 

Silver 

Steel  

Tin 

Zinc    . 


c. 

0.029 
0.475 
1.250 

0.10  to  0.071 
0.017 

0.30    to  0.18 
0.024 

0.120  to  0.10 
0.207 
0.455 
0.953 
0.15 

0.435  to  0.340 
0.15  to  0.094 
0.016 

0.50  to  0.168 
0.10 
0.065 


a. 

0.0039 
0.0041 
0.0037 
0.0016 
0.0041 
0.0003 
0.0040 
0.0048 
0.0039 
0.00002 
0.0009 
0.0036 
0.000025, 
0.0024 
0.0038 
0.0040 
0.0042 
0.0040 


26  ELECTRO-DEPOSITION    OP    METALS. 

From  the  above  table  it  will  be  seen  that  silver  is  the  best 
conductor,  then  copper,  the  specific  resistance  of  which  is 
slightly  greater,  next  gold,  aluminium,  and  so  on.  The  great- 
est specific  resistance  in  descending  series  bave  mercury,  man- 
ganin,  nickelin,  German  silver,  these  metals  or  metallic  alloys 
showing  at  the  same  time  the  slightest  change  in  resistance  at 
a  higher  temperature. 

Coefficient  of  temperature.  One  and  the  same  material  has 
the  same  specific  resistance  only  at  the  same  temperature.  In 
conductors  of  the  first  class — the  metals — the  resistance  in- 
creases, though  even  only  in  a  slight  degree,  as  the  tempera- 
ture increases.  The  formula  for  this  is  : 

(8)Wt9==Wt1   [+a(t2--tO], 

in  which  Wt2  is  the  resistance  at  the  higher  temperature  t2, 
and  Wt1?  the  resistance  at  the  lower  temperature  tl5  and  the 
magnitude  a,  the  number  of  ohms  the  resistance  increases  by 
a  rise  of  1°  C.  in  the  temperature. 

In.  the  conductors  pf  the  second  class — the  electrolytes — the 
resistance  decreases,  as  a  rule  quite  considerably  with  a  rise 
in  the  temperature,  and  is  calculated  from  the  following 
•equation  : 

(9)  Wt2  =  Wta  [1— a  (ta— 10]. 

The  magnitude  a  is  called  the  coefficient  of  temperature  of 
a  material,  and  these  coefficients  are  given  in  the  second 
column  of  the  above  table. 

Law  of  Kirchhoff.  From  a  water-conduit,  the  water  may 
by  means  of  branch-pipes  be  conducted  to  different  points. 
In  the  same  manner,  the  electric  current  may  be  conducted 
from  the  main  wire  by  means  of  different  wires  to  different 
places.  This  is  called  branching  or  distributing  the  current. 
The  wire  from  the  source  of  current  up  to  the  point  of  branch- 
ing is  known  as  the  main  wire  and  the  wires  branching  off  as 
branch  wires. 

The  heavy  lines  in  Fig.  6  represent  the  main  wires  ;  a  is  the 
junction  from  which  three  wires,  1,  2,  and  3,  branch  off,  and  b, 
the  junction  at  which  they  meet.  If  a  current-meter  (see  later 


MAGNETISM    AND    ELECTRICITY. 


27 


on)  be  placed  in  the  main  wire,  and  one  in  each  of  the  branch 
wires,  it  will  be  found  that  the  sum  of  the  current-quantities 
flowing  through  the  separate  branch  wires  is  equal  to  the 
current-quantity  in- the  main  wire.  .If,  however,  the  current- 
quantities  which  flow  through  the  separate  branch  wires  of 
the  same  cross-section,  1,  2,  3,  are  examined,  it  will  be  seen 
that  these  current-quantities  are  not  the  same,  but  vary  one 
from  the  other,  the  current-quantity  flowing  in  the  branch 
wire  1  being  greater  than  that  in  2  or'3,  while  that  in  2  is 
greater  than  that  in  3.  These  variations  are  due  to  the  fact 

FIG.  6. 


that  the  branch  wire  1  is  shorter  than  2  or  3,  and  hence  pos- 
sesses less  resistance.  Suppose  that  the  longest  branch-wire, 
3,  had  a  much  larger  cross-section  than  the  branch-wires  1 
and  2.  By  reason  of  its  slighter  resistance  more  current 
would  flow  through  it,  notwithstanding  its  length,  than 
through  1  and  2. 

Hence  the  law  of  Kirchhoff  may  be  summed  up  as  follows  : 

1.  When  the  current  is  branched  the  sum  of  the  current-strengths 
in  the  separate  branch  wires  is  exactly  as  great  as  the  current- 
strength  before  and  after  branching  off. 

2.  The  current-strengths  in  the  separate  branch-wires  distribute 
themselves  in  inverse  proportion  to  tlieir  resistances. 

In  the  practical  part  of  this  work  the  further  conclusions 
resulting  from  the  law  of  KirchhofF  will  be  referred  to. 


28  ELECTRO-DEPOSITION    OF    METALS. 

Law  of  Joule. — If  a  current  flows  through  a  conductor 
which  possesses  not  too  slight  a  resistance,  the  latter  becomes 
heated,  and,  hence,  electric  energy  is  converted  into  heat.  It 
has  been  shown  by  experiments  that  the  quantity  of  heat, 
which  is  produced  by  the  passage  of  a  determined  current- 
strength  through  a  determined  resistance,  increases  in  the 
same  ratio  as  the  duration  of  the  passage  of  the  current.  It 
has  also  been  shown  that  by  the  passage  of  a  determined 
current-strength  through  a  resistance,  the  heat  produced  in 
the  latter  in  a  determined  time  is  proportional  to  the  magni- 
tude of  the  resistance,  and,  hence,  that  the  quantity  of  heat 
becomes  larger  as  the  resistance  increases.  It  has  further 
been  established  that  the  quantity  of  heat  produced  in  a  de- 
termined resistance  during  a  determined  space  of  time  by  the 
current  flowing  through  it,  is  proportional  to  the  square  of 
the  current  strength. 

From  these  propositions  determined  by  experiments,  the 
law  of  Joule  may  be  brought  into  the  formula : 

(10)  Q  =  C.  J2.  W.  t. 

If  Q  is  the  quantity  of  heat  developed  in  calories,  J  is  the 
current-strength  in  amperes  which  flows  through  the  resist- 
ance, W  the  resistance  through  which  J  flows,  and  t  the  space 
of  time  in  seconds  of  the  passage  of  the- current ;  C  is  a  con- 
stant which  by  experiments  has  been  ascertained  as  0.0002392. 
In  words,  Joule's  law,  therefore,  reads:  The  quantity  of  heat 
produced  in  t  seconds  by  the  passage  of  a  current-strength  J  through 
the  resistance  W  is  proportional  to  the  expression  J2  Wt. 

Frictional  Electricity. 

In  an  ordinary  state  solid  bodies  exhibit  no  attractive  effect 
upon  such  light  particles  as  strips  of  paper,  balls  of  elderpith, 
etc.,  but  by  being  rubbed  with  a  dry  cloth  or  fur,  many  solid 
bodies  acquire  the  property  of  attracting  such  light  bodies  as 
mentioned  above.  The  cause  of  this  phenomenon  is  called 
electricity,  and  the  bodies  which  possess  this  property  of  be- 
coming electric  by  friction  are  termed  idio-electrics,  and  those 


MAGNETISM    AND    ELECTRICITY.  29 

which  do  not  appear  to  possess  it,  non-electrics.  Gray,  in  1727, 
found  that  all  non-electric  bodies  conduct  electricity,  and  hence 
are  conductors,  while  those  which  become  electric  by  friction 
are  non-conductors  of  electricity.  Strictly  speaking,  there  are 
no  non-conductors,  because  the  resins,  silk,  glass,  etc.,  conduct 
electricity,  though  only  very  badly.  It  is  therefore  better  to 
distinguish  good  and  bad  conductors.  To  test  whether  a  body 
belongs  to  the  idio-electrics,  the  so-called  electroscope  is  used, 
which  in  its  simplest  form  consists  of  a  glass  rod  mounted  on  a 
stand,  and  bent  at  the  top  into  a  hook,  from  which  hangs  by  a 
silken  thread  or  hair  a  pith  ball.  If,  on  bringing  the  rubbed 
body  near  the  pith  ball,  the  latter  is  attracted,  the  body  is" 
electric ;  whilst  if  the  ball  is  not  attracted,  the  body  is  either 
non-electric,  or  its  electricity  is  too  slight  to  produce  an  attrac- 
tive effect. 

From  the  following  experiments  it  was  found  that  there  exist 
two  kinds  of  electricity:  When  a  rubbed  rod  of  glass  or  shellac 
is  brought  near  the  ball  of  elder-pith  suspended  to  a  silk  thread, 
the  ball  is  attracted,  touches  the  rod,  adheres  for  a  few  moments, 
and  is  then  repelled.  This  repulsion  is  due  to  the  fact  that  the 
ball  by  coming  in  contact  with  the  rod  becomes  itself  electric, 
and  its  electricity  must  first  be  withdrawn  by  touching  with 
the  hand  before  it  can  again  be  attracted  by  the  rod.  By  now 
taking  two  such  balls,  one  of  which  has  been  made  electric  by 
touching  with  a  glass  rod,  which  had  been  rubbed  with  silk, 
and  the  other  by  touching  with  a  shellac  rod  rubbed  with  cloth, 
it  will  be  observed  that  the  ball,  which  is  repelled  by  the  glass 
rod,  is  attracted  by  the  shellac  rod,  and  vice  versa.  These  two 
kinds  of  electricity  are  called  vitreous  or  positive,  and  resinous 
or  negative  electricity,  and  it  has  been  found  that  electricities 
of  a  similar  name  attract,  and  electricities  of  an  opposite  name 
repel  each  other. 

Contact  Electricity. 

However,  a  current  of  electricity  is  generated  not  only  by 
friction,  but  also  by  the  contact  of  various  metals.  In  the 


30  ELECTRO-DEPOSITION    OF    METALS. 

same  manner  as  the  copper  and  iron  in  Galvani's  experiments 
with  the  frog-leg,  other  metals  and  conductors  of  electricity 
also  become  electric  by  contact,  the  electric  charges,  being, 
however,  stronger  or  weaker,  according  to  the  nature  of  the 
metals.  If  zinc  be  brought  in  contact  with  platinum,  it  be- 
comes more  strongly  positively  electric  than  when  in  contact 
with  copper ;  whilst,  however,  copper  in  contact  with  zinc  is 
negatively  excited,  in  contact  with  platinum  it  becomes  posi- 
tively electric. 

The  metal  which  has  become  positively  electric  is  said  to 
have  the  higher  potential,  i.  e.,  it  possesses  a  larger  measure  of 
electricity  than  the  metal  which  has  become  negatively  elec- 
tric, and  as  the  flow  of  water  from  higher  to  lower  points 
takes  place  in  a  larger  degree  the  greater  the  difference  in 
altitude  is,  the  electric  current  flows  also  the  more  rapidly 
from  a  positively  charged  body — the  positive  pole — to  the 
negatively  charged  body — the  negative  pole — the  greater  the 
difference  in  their  charges  is,  and  this  difference  in  the  charges 
of  two  bodies  is  called  difference  of  potential. 

If  now  the  metals  be  arranged  in  a  series  so  that  each  pre- 
ceding metal  becomes  positively  electric  in  contact  with  the 
succeeding  one,  a  series  of  electro-motive  force  is  obtained  in 
which  the  metals  or  conductors  of  electricity  stand  as  follows: 
Potassium,  sodium,  magnesium,  aluminium,  zinc,  cadmium, 
iron,  nickel,  lead,  tin,  copper,  silver,  mercury,  gold,  platinum, 
antimony,  graphite. 

While  two  metals  of  the  series  of  electro-motive  force  touch- 
ing each  other,  become  electrically  excited  in  such  a  manner 
that  one  becomes  positively  and  the  other  negatively  electric, 
an  exchange  of  the  opposite  electricities  takes  place  by  intro- 
ducing a  conducting  fluid  between  the  metals.  Thus,  if  a 
plate  of  zinc  and  a  plate  of  copper  connected  by  a  metallic 
wire  are  immersed  in  a  conducting  fluid,  for  instance,  dilute 
sulphuric  acid,  the  electricity  of  the  positive  zinc  passes 
through  the  fluid  to  the  negative  copper,  and  returns  through 
the  wire — the  closed  circuit — to  the  zinc.  However,  in  the 


MAGNETISM    AND    ELECTRICITY.  31 

same  degree  with  which  the  electricities  equalize  themselves, 
new  quantities  of  them  are  constantly  formed  on  the  points  of 
contact  of  the  metals  with  the  conducting  fluid ;  and,  hence, 
the  flow  of  electricity  is  continuous.  This  electric  current 
generated  by  the  contact  of  metals  and  fluids  is  called  the 
galvanic  current;  or,  since  it  is  generated  by  the  intervention 
of  fluid  conductors,  hydro-electric  current. 

A  combination  of  conductors  which  yield  such  a  galvanic 
current  is  called  a  galvanic  or  voltaic  cell  or  battery,  and  the 
production  of  current  from  the  above-mentioned  differences  of 
potential  of  the  metals  was  formerly  explained  by  the  suppo- 
sition that  chemical  processes  take  place  in  the  solutions  in 
which  the  metal  plate  is  immersed.  However,  as  will  be  seen 
later  on,  the  production  of  the  current  is  at  present  reduced, 
according  to  Nernst's  theory,  to  the  solution-pressure  and  the 
osmotic  pressure.  It  is  first  of  all  necessary  to  explain  the 
fundamental  chemical  principles,  since  without  a  knowledge 
of  them,  the  subsequent  sections  could  not  be  understood. 

Fundamental  Chemical  Principles. 

The  phenomena  presented  by  magnetism  and  electricity 
have,  so  far  as  required  for  our  .purposes,  been  briefly  discussed 
in  the  preceding  sections.  All  these  phenomena,  no  matter 
how  much  they  may  vary  in  their  nature,  have  this  in  com- 
mon, that  the  bodies  in  which  they  appear  undergo  no  change 
in  substance  and  weight,  notwithstanding  that  they  acquire 
the  most  diverse  properties.  If,  for  instance,  steel  by  being 
rubbed  with  a  magnet  has  acquired  the  power  of  attracting 
iron  articles,  and  hence  has  become  a  magnet  itself,  no  other 
changes  can  be  noticed  in  it,  even  by  the  most  minute  ex- 
amination ;  it  remains  the  same  steel  which  had  been  origin- 
ally used,  it  having  solely  acquired  the  property  of  being 
capable  of  acting  as  a  magnet. 

The  phenomena  to  be  treated  of  in  this  section  devoted  to- 
the  fundamental  chemical  principles,  are  of  an  entirely  dif- 
ferent nature,  we  having  constantly  to  deal  with  changes  in 
substance,  as  may  be  shown  by  the  following  examples. 


32  ELECTRO-DEPOSITION    OF    METALS. 

When  bright  iron  or  steel  is  exposed  to  the  action  of  moist 
air,  it  becomes  gradually  coated  with  a  brown-red  powder 
known  as  rust,  which  is  formed  by  the  iron  combining  with 
the  oxygen  of  the  air.  On  examining  this  brown-red  sub- 
stance it  will  be  found  to  possess  entirely  different  properties 
from  iron,  and  that  the  latter  has  undergone  a  material  change. 
By  the  absorption  of  oxygen  the  iron  has  been  converted  into 
an  oxide  of  iron,  and  a  process  known  as  a  chemical  process 
has  taken  place,  whereby  from  two  different  substances  a  third 
one  is  formed  which  possesses  other  properties,  and  is  of  a 
different  composition. 

The  phenomena  which  appear  in  subjecting  the  well-known 
red  oxide  of  mercury  or  red  precipitate  to  the  action  of  heat, 
furnish  another  example  of  a  chemical  process.  If  red  oxide 
of  mercury  be  heated  in  a  test-tube,  its  red  color  soon  dis- 
appears, its  bulk  decreases,  and,  if  heating  be  for  some  time 
continued,  it  disappears  entirely.  On  the  other  hand,  there 
will  be  found  deposited  upon  the  upper,  cooler  portions  of  the 
tube,  metallic  mercury  in  its  characteristic  form  of  globules. 
If  the  gaseous  products  evolved  during  the  process  be  also 
caught,  a  gas,  different  in  its  nature  from  air,  is  obtained, 
which  will  inflame  a  mere  spark  on  wood.  This  gas  is  the 
well-known  oxygen,  which  plays  such  an  important  part  in  the 
respiratory  process  of  human  beings  and  animals. 

While  by  the  formation  of  a  new  body  in  consequence  of 
the  combination  of  different  substances,  the  first  example 
presents  a  chemical  process  of  a  synthetic,  i.  e.,  building-up, 
nature,  the  second  one,  shows  a  process  of  an  analytical,  i.  e., 
resolving,  nature.  We  have  thus  learned  the  nature  of  the 
chemical  processes  in  general,  which,  no  matter  how  diverse 
the  separate  processes  may  be,  consist,  in  that  an  alteration  in 
the  material  nature  of  the  bodies  takes  place.  If  the  quanti- 
ties by  weight  of  a  substance  entering  into  a  chemical  change 
be  determined,  it  will  be  noticed  that  in  all  transpositions,  in 
the  decomposition  of  a  compound  into  its  constituents,  and  in 
the  union  of  the  elements  to  form  compound  bodies,  loss  in 


MAGNETISM    AND    ELECTRICITY.  33 

weight  never  occurs.  The  weight  of  the  resulting  compound  is 
invariably  equal  to  the  sum  of  the  weight  of  the  bodies  entering 
into  the  reaction.  This  furnishes  proof  that  the  most  import- 
ant law  of  the  indestructibility  and  non-creation  of  weighable 
substance  in  nature,  which  is  known  as  the  law  of  the  conserva- 
tion of  matter,  is  also  valid  as  regards  chemical  processes. 

Moreover,  we  find  the  further  conformity  to  law'  that  the 
quantities  by  weight  of  the  substances  formed  by  their  mutual 
action  in  a  chemical  process,  stand  one  to  the  other  in  a  fixed, 
unchangeable  proportion.  Thus,  for  instance,  a  given  quan- 
tity by  weight  of  iron  can  only  combine,  under  the  co-opera- 
tion of  water,  with  an  unchangeable  quantity  of  oxygen,  to 
ferric  hydroxide  (rust) ;  and  the  quantities  by  weight  of 
mercury  and  oxygen  formed  from  red  oxide  of  mercury, 
must  always  stand  one  to  the  other  in  an  unchangeable  pro- 
portion. 

If  now  in  a  similar  manner  as  in  the  second  example,  all 
the  bodies  offered  by  nature  be  decomposed  by  means  of  the 
auxiliary  agents  at  our  command,  into  such  constituents  as  do 
not  allow  of  a  division  into  further  substances,  it  will  be  found 
that  there  are  altogether  comparatively  few  substances  which 
•compose  the  bodies  of  nature.  Such  substances  are  called 
•chemical  elements;  they  cannot  be  converted  into  each  other^ 
but  constitute,  as  it  were,  the  limit  of  chemical  change.  At 
present  79  such  elements  are  known. 

The  smallest  portion  of  an  element,  or  of  a  chemical  com- 
pound, which  can  exist  in  a  free  state,  is  called  a  molecule.  If, 
for  instance,  common  salt  be  triturated  to  such  a  fine  powder 
that  further  reduction  by  mechanical  means  is  impossible,  such 
finest  particle  represents  the  molecule.  However,  common 
salt  consists  of  two  elements,  namely,  sodium  and  chlorine. 
Consequently  both  these  elements  must  be  present  in  the  mole- 
cule, and  these  smallest  particles  of  the  elements,  which  are 
contained  in  the  molecule,  are  called  atoms.  Hence  the  atom 
of  an  element  is  the  smallest  quantity  of  it  which  takes  part  in 
•chemical  combinations.  As  a  rule,  the  atom  sis  equal  to  half 
3 


34  ELECTRO-DEPOSITION    OF    METALS. 

the  molecule.     Hence,  for  the  formation  of  a  molecule  at  least, 
two  atoms  of  an  element  are  required. 

The  atoms  of  the  elements  aggregate  according  to  fixed  pro- 
portions by  weight,  and  the  smallest  quantities  by  weight  of 
the  elements  which  enter  into  combinations  with  each  other 
are  called  their  atomic  weights,  the  weight  of  hydrogen,  which 
is  the  lighest  of  all  the  elements,  being  taken  as  the  unit.  It 
must,  however,  be  stated  that  a  series  of  elements  may  unite 
not  only  in  a  single  proportion  of  weight,  but  also  in  several 
different  ones,  forming  thereby  combinations  of  entirely  dif- 
ferent properties.  If,  however,  these  different  proportions  by 
weight  are  more  closely  compared,  they  will  be  found  to  stand 
in  quite  simple  relations  to  each  other,  the  higher  being  always 
a  simple  multiple  of  the  lowest. 

In  the  table  below  are  given  the  most  important  chemical 
elements,  together  with  their  atomic  weights.  In  addition  the 
table  contains  the  symbols  used  for  designating  the  .elements. 
These  symbols  are  formed  from  the  first  letters  of  their  names, 
derived  either  from  the  Latin  or  Greek.  Hydrogen  is,  for  in- 
stance, represented  by  the  letter  H,  from  the  word  Hydrogenium; 
Oxygen  by  0,  from  oxygenium;  Silver  by  Ag,  from  argentum. 
If  Latin  or  Greek  names  of  several  elements  have  the  same 
first  letters,  the  latter  serves  only  for  the  designation  of  one  of 
these  elements,  while  for  the  other  elements,  the  first  letter  is 
furnished  with  an  additional  characteristic  letter.  Thus,  for 
instance,  boron  is  represented  by  the  letter  B ;  barium  by  Ba ; 
bismuth  by  Bi ;  bromine  by  Br. 


MAGNETISM    AND    ELECTRICITY. 


35 


INTERNATIONAL  TABLE  OF  THE  ATOMIC  WEIGHTS  OF  THE  MOST  IMPORTANT 

ELEMENTS,  (1911). 


Name  of  Element. 

Symbol. 

Atomic 
Weight. 

Name  of  Element. 

Symbol. 

Atomic 
Weight. 

Aluminium  .... 
Antimony  

Al 

Sb 

As 

27.1 
120.2 

74  96 

Lead  
Magnesium  .    .    . 
Manganese  . 

Pb 
Mg 
Mn 

207.10 
24.32 
54.93 

Ba 

137  37 

Mercury  ..... 

Hg 

200.0 

Bismuth   

Bi 

208.0 

M 

58.68 

B 

11  0 

Nitrogen       . 

N 

14.01 

Br 

79  92 

Osmium    ... 

Os 

190.9 

Cd 

112.40 

o 

16.00 

Ca 

40  09 

Phosphorus  .  .        .  - 

p 

31.04 

Carbon              • 

C 

12  0 

Platinum      .    .        . 

Pt 

195.2 

Chlorine  ..... 

Cl 
Cr 

35.46 
52  0 

Potassium  ... 

K 

Se 

39.10 

79  2 

Cobalt  ... 

Co 

58.97 

Si 

28.3 

Cu 

63  57 

Silver 

Ae- 

107  88 

Fluorine  .... 

F 

19.0 

Sodium  

& 
Na 

23.00 

Gold             -    ... 

Au 

197  2 

S 

32.07 

H 

1  008 

Tin           .    .    . 

Sn 

119  0 

Iodine       .... 

I 

126.92 

Zinc    

Zn 

65.37 

Fe 

55.85 

The  symbols  not  only  represent  the  elementary  bodies,  but 
also  their  fixed  quantities  by  weight,  so  that,  for  instance,  the 
symbol  Ni  means  58.68  parts  by  weight  of  nickel. 

Compounds  produced  by  the  union  of  the  elements  are 
represented  by  placing  their  corresponding  symbols  together 
and  designating  them  chemical  formulas.  As  previously  men- 
tioned, common  salt  consists  of  one  atom  sodium  (Na)  and 
one  atom  chlorine  (Cl),  and  hence  its  formula  has  to  be  written 
NaCl.  The  latter  shows  that  one  molecule  of  common  salt 
consists  of  23.00  parts  by  weight  of  sodium  and  35.46  parts  by 
weight  of  chlorine,  which  together  form  58.46  parts  by  weight 
of  common  salt.  If  several  atoms  of  an  element  are  present 
in  a  compound,  this  is  denoted  by  numbers  which  are  written 
to  the  right  of  the  symbol,  below,  as  proposed  by  Poggendorf, 
or  above,  as  proposed  by  Berzelius,  and  still  used  at  the  pres- 
ent by  a  few  people.  Water,  for  instance,  contains  2  atoms 
hydrogen  (H)  and  one  atom  oxygen  (0),  and  hence  its  formula 


36  ELECTRO-DEPOSITION    OF    METALS. 

is  H20,  which  indicates  that  2  parts  by  weight  of  hydrogen, 
together  with  16  parts  by  weight  of  oxygen,  form  18.016  parts 
by  weight  of  water. 

The  symbols  may  be  said  to  constitute  the  chemical  alpha- 
bet and  the  formulas  may  be  considered  as  the  words  of  the 
chemical  language.  By  means  of  the  symbols  and  formulas 
it  is  made  possible,  to  express  in  the  most  simple  manner,  the 
chemical  processes  by  equations,  which  not  only  denote  the 
manner  of  the  chemical  transposition,  but  also  allow  of  the 
calculation  of  the  quantities  by  weight  which  have  entered 
into  reaction  in  the  transposition  of  the  different  substances. 
If,  according  to  this  our  former  examples,  by  means  of  which 
it  has  been  endeavored  to  explain  the  nature  of  a  chemical 
process,  be  translated  into  this  chemical  language,  the  equa- 
tions read  as  follows : 

1.   2Fe2  +  302  +  6H20  =  4Fes(OH)8. 

Iron.       Oxygen.       Water.       Ferric  hydroxide. 

2.    2HgO  ==  Hg2  +  02. 

Mercuric  oxide.  Mercury.  Oxygen. 

Valence  of  the  elements.  If  the  combinations  into  which  the 
elements  enter  one  with  the  other  are  more  closely  examined, 
and  their  formulas  compared,  it  will  be  seen  that  entire  groups 
of  combinations  are  composed  in  an  analogous  manner.  This 
analogy  of  composition  appears  very  plainly  in  the  compounds 
into  which  a  series  of  elements  enters  with  hydrogen,  and  we 
thus  come  across  four  different  groups  of  compounds.  The 
elements  of  the  first  group,  namely,  of  the  halogens,  chlorine, 
bromine,  iodine  and  fluorine,  combine  with  one  atom  of 
hydrogen  ;  those  of  the  second  group,  to  which  belong  oxygen 
and  sulphur,  are  capable  of  saturating  two  atoms  of  hydrogen  ; 
those  of  the  third  group,  which  embraces  nitrogen,  phos- 
phorus, arsenic  and  antimony,  fix  three  atoms  of  hydrogen, 
and  finally,  the  elements  of  the  fourth  group,  carbon  arid 
silicon,  may  combine  with  four  atoms  of  hydrogen.  Hence, 
we  must  ascribe  a  particular  function  of  affinity  to  each  ele- 


MAGNETISM    AND    ELECTRICITY.  37 

ment  in  its  relation  to  hydrogen,  and  this  property  is  called 
valence. 

Now,  according  as  the  elements  are  capable  of  combining 
with  one,  two,  three  or  four  atoms  of  hydrogen,  they  are 
designated  as  univalent,  bivalent,  trivalent,  or  quadrivalent ; 
and  all  elements,  which  possess  the  same  valence,  are  called 
chemically  equivalent.  In  chemical  compounds,  such  equiv- 
alent elements  may  replace  each  other  atom  for  atom,  such 
substitution  being  also  possible  in  elements  of  dissimilar  val- 
ence, but  it  must  take  place  in  such  a  manner  that  a  bivalent 
atom  replaces  two  hydrogen  atoms,  a  trivalent  atom  three 
hydrogen  atoms,  so  that  an  equal  number  of  valences  is  always 
exchanged.  Thus,  in  accordance  with  this,  one  atom  of 
chlorine  is  equivalent  to  one  atom  of  hydrogen  and  hence, 
when  a  substitution  of  hydrogen  by  chlorine  results,  it  can 
only  be  by  one  atom  of  chlorine  taking  the  place  of  one  atom 
of  hydrogen.  Hence  it  follows  that  35.46  parts  by  weight  of 
chlorine  are  equivalent  to  one  part  by  weight  of  hydrogen. 
On  the  other  hand,  one  atom  of  oxygen  is  equivalent  to  two 
atoms  of  hydrogen,  or  16  parts  by  weight  of  the  former  are 
equivalent  to  2  parts  by  weight  of  the  latter.  A  mutual  sub- 
stitution of  these  two  elements  must,  therefore,  always  take 
place  in  the  proportion  of  16  to  2.  Since  the  elements,  nitro- 
gen, phosphorus,  etc.,  are  capable  of  fixing  3  hydrogen  atoms, 
mutual  substitution  must  also  take  place  in  such  a  man- 
ner that  1  nitrogen  atom  replaces  3  hydrogen  atoms  or  that 

— : —  =  4.67  parts  by  weight  of  nitrogen  are  substituted  for  1 
o 

part  by  weight  of  hydrogen.  Finally,  one  atom  of  carbon  or 
of  silicon  is  equivalent  to  4  parts  by  weight  of  hydrogen,  or 
1  part  by  weight  of  hydrogen  is  replaced  by  3  parts  by  weight 
of  carbon.  These  quantities  by  weight  determined  for  some 
of  the  elements,  which  are  equivalent  to  1  part  by  weight  of 
hydrogen,  or,  in  general,  to  one  part  by  weight  of  a  univalent 
element,  are  called  equivalent  weights  or  combining  weights,  and 
are  in  a  similar  manner  deduced  for  all  the  other  elements. 


38  ELECTRO-DEPOSITION    OF    METALS. 

While  the  elements  preserve  a  constant  valence  towards 
hydrogen,  many  of  them  show  a  varying  valence,  which 
differs  also  from  the  hydrogen-valence  towards  other  elements, 
so  that,  for  instance,  the  same  element  may  appear  opposite  to 
a  second  one,  trivalent  in  one  combination  and  quinquivalent 
in  another.  Combinations  of  phosphorus  with  chlorine  may 
serve  as  an  example.  Together  they  form  a  combination, 
PCI  3,  as  well  as  one  PC15  ;  in  the  first  case  3  atoms  of  chlor- 
ine or  3  X  35.46  parts  by  weight  are  equivalent  to  1  atom  of 
phosphorus  or  31.04  parts  by  weight.  This  capacity  of  differ- 
ent elements  of  being  endowed  with  totally  unequal  valence, 
forces  us  to  the  assumption  that  valence  is  not  a  characteristic 
property  of  the  elements,  but  is  dependent  on  the  nature  of  the 
elements  combining  with  each  other,  and  is  also  influenced 
by  the  conditions  under  which  the  formation  of  the  chemical 
combination  takes  place.  1 

By  arranging  the  most  important  elements  according  to 
their  valence,  we  obtain  the  following  groups  : 

Vnivalent  elements :  Hydrogen,  chlorine,  bromine,  iodine, 

fluorine,  potassium,  sodium,  silver. 

Bivalent  elements:  Oxygen,  sulphur,  barium,  strontium, 
calcium,  magnesium,  cadmium,  zinc,  lead,  copper, 
mercury. 

Bivalent  and  trivalent  elements :  Iron,  cobalt,  nickel,  man- 
ganese. 

Trivalent  elements :  Boron,  aluminium,  gold. 
Trivalent  and  quinquivalent  elements :  Oxygen,  phosphorus, 

arsenic,  antimony,  bismuth. 

Quadrivalent  elements :  Carbon,  silicon,  tin,  platinum. 
Later  on,  in  the  section  on  the  fundamental  principles  of 
electro-chemistry,  in  speaking  of  the  development  of  the  laws 
of  Faraday,  these  groups  will  have  to  be  referred  to,  and  their 
importance  will  then  become  evident. 

Metals  and  non-metals.  In  accordance  with  the  greater  or 
less  conformity  of  their  physical  properties,  the  elements  have, 
for  the  sake  of  expediency,  been  sub-divided  into  two  sections, 


MAGNETISM    AND    ELECTRICITY.  39 

namely  metals  and  non-metals,  the  latter  being  also  called 
metalloids.  The  first  section  embraces  the  elements  the  prin- 
ciple characteristics  of  which  are  that  they  show  metallic 
luster,  are  opaque  or  at  the  utmost  translucent  in  thin  laminae, 
are,  as  a  rule,  fairly  malleable  and  ductile,  and  with  the  one 
•exception  of  mercury,  are  all  solid  bodies  at  ordinary  temper- 
atures and  pressures,  and  are  good  conductors  of  heat  and 
electricity.  All  the  other  elements  which  have  not  such 
physical  properties  in  common  are  classed  as  metalloids.  The 
two  groups  of  bodies  obtained  by  this  mode  of  division  also 
show  in  a  chemical  respect  such  similarities  as  to  justify  this 
classification,  the  metalloids  forming  with  hydrogen  readily 
volatile,  mostly  gaseous,  combinations,  while  the  metals  unite 
more  rarely  with  hydrogen,  and,  at  any  rate,  do  not  form 
volatile  combinations  with  it.  The  combinations  which  the 
metalloids  form  with  oxygen  also  show,  in  their  behavior 
towards  water,  very  characteristic  phenomena,  entirely  differ- 
ent from  those  presented  by  compounds  of  the  metals  with 
oxygen.  These  differences  will  later  on  be  referred  to  in  de- 
tail. A  very  remarkable  difference  of  the  utmost  importance, 
•especially  for  our  purpose,  is  in  the  action  of  the  electric  cur- 
rent upon  the  combinations  between  metals  and  metalloids, 
the  metals  being  always  deposited  on  the  electro-negative  pole, 
and  the  metalloids  on  the  electro-positive  pole. 

However,  notwithstanding  these  properties,  differing  on  the 
•one  hand  and  corresponding  on  the  other,  a  sharp  separation 
•of  the  elements  based  upon  the  above-mentioned  considera- 
tions cannot  be  reached,  and  the  classification  as  regards  some 
elements  turns  out  different  according  to  whether  one  or  the 
•other  behavior  is  first  taken  into  consideration. 

On  the  other  hand,  a  classification  free  from  ambiguity  re- 
sults from  adhering,  as  is  now  also  done  in  science,  to  the  be- 
havior of  the  elements  towards  salts  as  the  distinctive  principle. 
In  this  manner  two  sharply-defined  groups  are  obtainable,  one 
comprising  the  elements — the  metals — capable  of  evolving 
hydrogen  with  the  acids,  while  the  elements  of  the  other  group 


40  ELECTRO-DEPOSITION    OF    METALS. 

do  not  possess  this  power,  and  are  classed  among  the  metal- 
loids.    From  this  results  the  following  classification  : 

Metalloids :  Chlorine,  bromine,  iodine,  fluorine,  oxygen, 
sulphur,  nitrogen,  phosphorus,  boron,  carbon,  silicon. 
Metals :  Potassium,  sodium,  lithium,  magnesium,  calcium, 
barium,  strontium,  aluminium,  zinc,  iron,  manganese, 
chromium,  nickel,  cobalt,  copper,  cadmium,  arsenic, 
antimony,  tin,  lead,  bismuth,  mercury,  silver,  gold, 
platinum. 

Acids,  bases,  salts.  Attention  has  previously  been  drawn  to 
the  difference  in  behavior  towards  water  of  combinations  of 
the  metalloids,  and  of  the  metals  with  oxygen,  and  this  be- 
havior will  have  to  be  somewhat  more  closely  considered, 
because  we  are  thereby  directed  to  extremely  important  classes 
of  chemical  combinations. 

Oxygen  is  the  most  widely  distributed  element,  it  forming, 
together  with  nitrogen,  air,  and  with  hydrogen,  water.  All 
the  elements,  with  the  exception  of  fluorine  and  a  few  more 
rare  ones,  show  great  affinity  for  it  and  enter  readily  into  re- 
action with  it.  In  the  processes  enacted  thereby,  the  large 
class  of  oxides  is  formed,  and  the  chemical  process  in  which 
an  absorption  of  oxygen  takes  place  is  generally  called  oxida- 
tion, while  the  term  reduction  is  applied  to  the  opposite  process 
by  which  a  withdrawal  of  oxygen  from  a  substance  is  effected. 
If  these  oxides,  with  the  exception  of  a  few  so-called  indif- 
ferent oxides,  be  brought  together  with  water,  they  impart  to 
it  either  an  acid  taste,  as, well  as  the  power  to  redden  blue 
litmus  and  to  evolve  hydrogen  with  metals,  or  they  give  to 
the  water  a  lye-like  taste  and  the  power  of  restoring  the  blue 
color  to  the  litmus  previously  reddened.  The  oxides  of  the 
first  kind  are  chiefly  formed  with  the  co-operation  of  the  ele- 
ments belonging  to  the  metalloids,  while  those  of  the  second 
class  contain  exclusively  metals  in  addition  to  oxygen. 

These  two  classes  of  bodies,  which  possess  entirely  different, 
even  directly  opposite,  properties,  are  the  acids  and  bases,  and 
will  have  to  be  separately  discussed. 


MAGNETISM    AND    ELECTRICITY.  '  41 

Acids.  As  characteristic  properties  of  the  acids  have  been 
mentioned,  their  acid  taste,  their  power  of  reddening  blue 
litmus,  and  to  evolve  hydrogen  with  metals,  magnesium  being 
especially  suitable  for  the  latter  purpose.  If  now  the  chemical 
compositions  of  all  the  compounds  which  possess  the  above- 
mentioned  properties  be  more  closely  examined,  they  will  be 
found  to  contain,  without  exception  and  without  regard  to 
their  own  constituents,  hydrogen  which  can  be  displaced  by 
metals.  This  hydrogen  may  be  present  in  the  combinations 
in  one  or  more  atoms,  and  according  to  the  number  of  the 
hydrogen-atoms  present,  a  distinction  is  made  between  "mono- 
basic, dibasic,  tribasic,  etc.,  acids. 

A  further  distinction  is  made  between  acids  containing  no 
oxygen,  to  which  belong  the  haloid  acids  for  instance,  hydro- 
chloric acid,  and  acids  containing  oxygen,  which  are  therefore 
called  oxy  acids.  The  latter  group  comprises  the  majority  of 
acids,  the  well-known  sulphuric  and  nitric  acids  belonging  to 
it.  However,  the  characteristic  feature  of  the  acids  consists 
solely  in  that  they  contain  hydrogen  which  can  be  displaced 
by  metals. 

Bases.  The  second  group  of  oxides  imparts  to  water,  as 
previously  mentioned,  a  lye-like  taste  and  the  power  to  restore 
the  blue  color  of  litmus  reddened  by  acid,  and  these  properties 
are  utilized  as  valuable  agents  for  the  characterization  of  the 
substances  as  bases.  Nevertheless,  by  the  above-mentioned 
definitions  the  meaning  of  bases  is  not  unequivocally  estab- . 
lished,  and  for  a  thorough  investigation  of  their  material 
nature,  their  exact  composition  has  to  be  determined  with  the 
assistance  of  analysis,  as  was  done  with  the  acids.  From  this 
it  results  that,  in  addition  to  metals  or  metal-like  groups  of 
atoms,  all  basic  compounds  contain  oxygen  and  hydrogen,  the 
latter  elements  being  always  present  in  the  same  number  of 
atoms,  namely,  in  the  form  of  hydroxyl  groups,  OH.  Accord- 
ing to  their  valence  the  metals  combine  with  one  or  more 
hydroxyl  groups  to  bases. 

Salts.     The  groups  of  chemical  combinations  above  referred 


42  ELECTRO-DEPOSITION    OF    METALS. 

to,  show  a  very  remarkable  behavior  in  so  far  that  by  their 
mutual  action  they  are  capable  of  equalizing  or  saturating 
their  characteristic  features,  so  that  by  means  of  a  basic  com- 
bination the  specific  properties  of  an  acid  can  be  removed, 
and  by  means  of  an  acid  the  specific  properties  of  a  bade. 

An  example  will  explain  this  process.  If  to  a  certain  quan- 
tity of  hydrochloric  acid  a  few  drops  of  blue  litmus  be  added, 
the  fluid  in  consequence  of  its  acid  properties  will  change  the 
blue  coloring  matter,  the  latter  acquiring  a  red  color.  By 
now  adding  drop  by  drop  dilute  soda  lye,  which  is  a  basic 
combination,  it  will  be  noticed  that  on  the  spot  where  the  lye 
falls  upon  the  acid,  the  red  color  disappears  momentarily,  and 
gives  way  to  a  blue  one.  If  the  addition  of  lye  be  carefully 
continued  and  the  fluid  constantly  stirred,  a  point  is  suddenly 
reached  when  by  a  single  drop  of  the  lye  the  red  color  of  the 
entire  fluid  is  removed  and  converted  into  pale  blue.  If  no 
more  lye  than  exactly  necessary  for  the  sudden  change  in 
color  has  been  brought  into  the  fluid,  the  latter  now  possesses 
neither  the  properties  of  an  acid  nor  of  a  base,  but  has  be- 
come what  is  called  neutral.  A  process  of  the  kind  above 
described,  by  which  the  acid  character  of  a  combination  is 
equalized  by  the  basic  character  of  another,  or  .vice  versa,  is  in 
chemistry  called  neutralization. 

This  example  shows,  that  it  is  frequently  of  importance  to 
know  whether  a  fluid  possesses  acid,  basic  or  neutral  prop- 
erties, or  as  it  also  expressed,  whether  it  shows  an  acid,  basic, 
or  neutral  reaction.  For  the  determination  of  these  properties 
so-called  reagent-papers  are  used.  They  consist  of  unsized 
paper  dyed  with  various  organic  coloring  matters,  preferably 
blue  litmus  tincture,  or  the  latter  slightly  reddened  by  acids. 
When  small  strips  of  such  papers  are  dipped  in  the  fluid  to  be 
examined,  blue  litmus  paper  will  be  colored  red  if  the  fluid 
has  an  acid  reaction,  and  red  litmus  paper,  blue,  if  it  shows  an 
alkaline  or  basic  reaction.  Finally,  fluids  which  change 
neither  blue  nor  red  litmus  paper  react  neutral,  or  they  show  a 
•neutral  reaction.  If  we  now  return  to  our  example  by  which 


MAGNETISM    AND    ELECTRICITY.  43 

the  process  of  neutralization  between  acid  and  base  has  been 
described,  it  will  above  all  be  of  interest  to  learn  whether  this 
•equalization  of  the  mutual  properties  runs  its  course  according 
to  fixed  laws,  and  what  the  nature  of  the  latter  is.  It  will  be 
further  desirable  to  gain  an  insight  into  the  chemical  trans- 
formations which  have  taken  place  in  the  process,  and  to  learn 
the  products  which  have  been  newly  formed. 

For  the  elucidation  of  these  questions,  let  us  take  a  deter- 
mined quantity  of  acid  and,  in  the  same  manner  as  in  the 
above-described  example,  add  to  it  lye  until  the  acid  is  just 
neutral,  this  being  shown  by  the  sudden  change  in  color  of 
the  litmus.  If  we  now  take  another  quantity  of  the  same  acid 
and  proceed  with  it  in  the  same  manner,  it  will  be  found  that 
the  consumed  quantities  of  bases  stand  in  the  same  proportion 
to  each  other  as  the  quantities  of  acid  used,  so  that  if,  in  one 
•case,  for  50  ccm.  of  acid  30  ccm.  of  lye  were  used  for  neutral- 
ization, in  the  other,  with  the  use  of  the  same  acid  and  the 
same  lye,  for  75  ccm.  of  acid  45  ccm.  of  lye  were  required  to 
obtain  a  neutral  solution.  By  repeating  these  experiments  with 
any  other  acids  and  bases,  the  same  conformity  to  law  will 
always  be  found,  and  it  will  thus  be  seen  that  neutralization 
between  acids  and  bases  runs  its  course  in  positively  fixed 
quantities,  and  that  for  the  neutralization  of  a  certain  quantity 
of  an  acid,  a  positively  fixed  quantity  of  a  base  is  required, 
and  vice  versa. 

Of  this  conformity  to  law  much  use  is  made  in  analytical 
chemistry  by  volumetric  methods  for  the  determination  of  the 
content  of  an  acid  by  means  of  a  base  of  known  content,  and 
vice  versa. 

lu  order  to  learn  what  new  products  are  formed  by  the 
neutralization  between  acids  and  bases,  the  neutral  solution 
obtained,  according  to  our  example,  is  concentrated  by  evapo- 
ration, and  it  will  be  found  that  from  the  fluid  separates  a 
white  substance  in  small  crystals  which,  according  to  analysis, 
consists  of  sodium  (Na)  and  chlorine  (Cl),  and  hence  consti- 
tutes the  well-known  common  salt  (NaCl).  However,  in  ad- 


44  ELECTRO-DEPOSITION    OF    METALS. 

dition  to  the  common  salt,  water  (H20)  has  also  been  formed 
by  the  chemical  process,  as  shown  by  analysis. 

If  now,  as  another  example,  we  take  as  an  acid,  sulphuric 
acid  (H2SO4).  neutralize  it  with  caustic  soda  (KOH),  and 
again  determine  the  products  formed,  we  arrive  at  a  substance, 
the  composition  of  which,  according  to  analysis,  is  K3S04, 
hence  represents  potassium  sulphate,  water  being  again  formed 
as  an  additional  product.  The  process  of  neutralization  takes 
its  course  in  an  analogous  manner  with  any  kinds  of  acids 
and  bases,  and  it  will  be  seen  that  every  neutralization  of  an 
acid  and  a  base  is  accompanied  by  the  formation  of  water, 
and  further,  that  after  the  withdrawal  of  the  hydrogen  from 
the  acid,  the  metal  of  the  bases  forms  with  the  remainder  a 
new  neutral  combination,  which  is  called  a  salt. 

These  processes  are  more  distinctly  presented  by  bringing 
them  into  chemical  formulas,  and  for  our  examples  we  have 
to  write 

HC1         +      NaOH       =  H20       +       NaCl. 

Hydrochloric  acid.     Sodium  hydrate.     Water.     Sodium  chloride  (common  salt). 

H2S04    +      2KOH      =  H20       4-       K2S04. 

Sulphuric  acid.     .  Potassium  hydrate.     Water.     Neutral  potassium  sulphate. 

These  formulas  show  plainly  the  connection  which  exists  be- 
tween the  acids,  bases  and  salts. 

The  formation  of  salts  from  the  acids  is  thus  brought  about 
by  the  replacement  of  the  hydrogen-atoms  of  the  acids  by 
metals.  However,  this  replacement  of  the  hydrogen  can 
only  take  place  in  accordance  with  the  valence  of  the  metal, 
so  that  a  univaluit  metal  can  take  the  place  of  only  one 
hydrogen-atom,  a  bivalent  metal  of  only  two  hydrogen-atoms, 
and  so  on.  With  the  use  of  a  monobasic  acid,  i.  e.,  one  in 
which  only  one  hydrogen-atom  is  contained  in  the  molecule, 
salts  can  only  be  prepared  which,  besides  metal,  contain  no 
free  hydrogen-atoms,  and  salts  of  the  above-mentioned  kind, 
namely,  neutral  salts,  are  exclusively  obtained.  By  taking, 


MAGNETISM    AND    ELECTRICITY.  45 

on  the  other  hand,  an  acid  with  several  bases,  its  hydrogen- 
atoms  can  be  either  partly  or  entirely  replaced  by  metals.  In 
the  first  case,  salts  result  which  still  possess  an  acid  character, 
they  containing  hydrogen  besides  a  metal,  and  are  called  acid 
salts,  while  in  the  latter  case  neutral  salts  are  formed,  with 
which  we  are  already  acquainted.  Sulphuric  acid  is  a  dibasic 
acid,  and,  hence,  contains  two  hydrogen-atoms  in  the  mole- 
cule. Let  us  take  as  an  example,  the  salts  which  sulphuric 
acid  is  capable  of  forming,  and  first  saturate  in  it  only  on6 
hydrogen-atom  by  a  univalent  metal,  for  instance,  sodium, 
by  adding  just  enough  soda  lye  to  the  soda  to  half  saturate  it. 
This  solution  still  shows  a  strong  acid  reaction,  and  by  suffi- 
ciently concentrating  it,  a  salt  is  separated  which  throughout 
possesses  acid  properties  and,  as  shown  by  analysis,  has  the 
chemical  formula  NaHS04.  It  is  different  from  the  neutral 
sodium  sulphate,  which  is  obtained  by  completely  saturating 
the  sulphuric  acid  with  caustic  soda,  i.  e.,  by  compounding 
the  sulphuric  acid  with  caustic  soda  up  to  the  neutral  reaction. 
The  two  processes  just  described  are  explained  by  the  follow- 
ing equations,  which  also  show  distinctly  the  difference 
between  neutral  and  acid  salts : 

1.  H2S04  +  NaOH  =  NaHS04  +  H20. 

Sulphuric  acid.         Sodium         Acid  sodium         Water, 
hydrate.  sulphate. 

2.  H2S04  +  2NaOH  =  =  Na2S04  +  H20. 

Sulphuric  acid          Sodium      Neutral  sodium        Water, 
hydrate.  sulphate. 

In  an  analogous  manner,  as  a  dibasic  acid  is  capable  of 
forming  two  series  of  salts,  three  series  of  salts  may  be  derived 
from  a  tribasic  acid,  for  instance,  phosphoric  acid,  so  that  in 
general  an  acid  of  several  bases  can  form  as  many  series  of 
acids  as  it  contains  hydrogen-atoms  in  the  molecule. 

Nomenclature  of  salts.  In  conformity  with  the  definition  of 
salts  given  above,  according  to  which  they  are  derived  from 
the  acids  by  the  replacement  of  the  hydrogen  by  metals,  they 


46  ELECTRO-DEPOSITION    OF    METALS. 

are  classified  according  to  the  acids  they  have  in  common,  the 
salts  derived  from  sulphuric  acid  being  thus  designated  sul- 
phates. For  the  sake  of  distinguishing  the  various  metallic 
salts  of  the  same  acid,  the  names  of  the  metals  are  added. 
Thus,  for  instance,  the  scientific  term  for  white  vitriol,  formed 
by  the  action  of  sulphuric  acid  upon  zinc,  is  zinc  sulphate. 
The  designations  for  the  salts  of  the  other  acids  are  formed  in 
the  same  manner ;  those  derived  from  nitric  acid  being  called 
nitrates,  from  phosphoric  acid,  phosphates,  etc.  Salts  in  which 
all  the  hydrogen-atoms  of  the  acids  from  which  they  are  de- 
rived, have  been  replaced  by  metal-atoms  are  called  neutral, 
normal,  or  primary  salts  in  contradistinction  to  the  acid  or 
secondary  salts  which,  besides  metal-atoms,  also  contain 
hydrogen-atoms  in  the  molecule.  Finally,  the  salts  are  also 
designated  by  indicating  with  the  assistance  of  the  Greek 
numerals,  mono-,  di-,  etc.,  the  number  of  metal-atoms  con- 
tained in  one  acid-molecule.  With  the  use  of  the  latter  mode 
of  designation,  the  scientific  term  for  the  acid  sodium  sulphate 
is  sodium  mono-sulphate,  and  for  the  neutral  sodium  sulphate, 
sodium  disulphate. 

Fundamental  Principles  of  Electro- Chemistry. 

Electrolytes.  Solutions  of  chemical  compounds  which  can 
be  decomposed  by  the  current,  are  called  electrolytes. 

A  distinction  is  made  between  conductors  and  non-conductors 
of  electricity,  and,  as  previously  mentioned,  the  metals  are 
conductors,  while  most  of  the  metalloids,  for  instance,  sulphur, 
do  not  transmit  the  electric  current. 

The  conductors  are  divided  into  conductors  of  the  first  class, 
to  which  belong  the  metals,  and  conductors  of  the  second  class, 
the  latter  being  chiefly  the  aqueous  solutions  of  metallic  salts 
and  certain  other  substances. 

The  conductors  of  the  first  class  do  not  experience  a  per- 
ceptible material  change  by  the  passage  of  the  current,  they 
being  at  the  utmost  heated  thereby.  On  the  other  hand,  the 
conductors  of  the  second  class  undergo,  by  the  passage  of  the 


MAGNETISM    AND    ELECTRICITY.  47 

current,  a  chemical  change  is  so  far  as  that  on  the  places 
where  the  current-carrying  metallic  conductor  enters  the 
solution,  the  constituents  of  the  latter  are  decomposed  and 
separated. 

This  phenomenon  of  the  chemical  decomposition  of  sub- 
stances or  compounds  by  means  of  an  electric  current  is  called 
electrolysis,  and  the  conductors  of  the  second  class  which 
undergo  such  decomposition,  are  termed  electrolytes. 

The  metal  plates  through  which  the  current  passes  in  and 
out  of  the  solution  are  called  electrodes,  the  positive  electrode 
through  which  the  current  enters  being  termed  anode,  and 
the  negative  electrode  through  which  it  leaves  the  electrolyte, 
cathode. 

Ions.  This  term  is  applied  to  the  constituents  into  which 
the  combinations  present  in  the  solution  are  decomposed  by 
the  current,  and  carried  to  the  cathodes  and  anodes. 

If  a  sodium  chloride  solution  be  subjected  to  electrolysis, 
the  sodium  chloride  is  decomposed,  chlorine  being  separated 
on  the  positive  electrode,  and  sodium  on  the  negative  electrode. 
Thus  chlorine  and  sodium  are  the  ions  of  sodium  chloride. 
If  an  acid  be  decomposed  by  the  electric  current,  hydrogen  is 
always  separated  on  the  negative  electrode,  and  the  other 
constituent  of  the  acid  on  the  positive  electrode. 

The  ions  separated  on  the  negative  electrodes  are  called 
cations  and,  hence,  in  the  above-mentioned  examples,  sodium 
and  hydrogen  are  the  cations  of  sodium  chloride,  or  of  the 
acid.  The  cations  migrate  from  the  positive  to  the  negative 
electrode. 

The  remaining  ions  of  the  combinations  migrate  from  the 
negative  to  the  positive  electrode  (anode),  and  are  there  sep- 
arated. These  ions  separated  on  the  anode  are  called  anions. 
Thus  chlorine  is  the  anion  of  sodium  chloride,  as  well  as  of 
hydrochloric  acid  and  of  other  chlorine  compounds. 

The  ions  exhibit,  partly,  properties  entirely  different  from 
the  elements  the  names  of  which  they  bear.  The  hydrogen- 
ion  of  the  acids,  for  instance,  is  not  known  as  a  gas,  but  only 


48  ELECTKO-DEPOSITION    OF    METALS. 

in  solution,  while  the  element  hydrogen  is  gaseous  and  but 
very  slightly  soluble  in  water.  Further,  while  the  hydrogen- 
ion  determines  the  characteristic  properties  of  the  acids,  hy- 
drogen gas  exhibits  none  of  these  properties,  and  the  hydrogen- 
ion  can  only  be  met  with  in  aqueous  solutions  of  acids  in 
which  are  at  the  same  time  present  the  other  constituents  of 
the  acids  possessing  ion-properties. 

If  in  hydrochloric  acid,  hydrogen  exists  as  ion,  chlorine 
must  be  the  other  ion,  because  this  acid  contains  no  other 
constituents,  and  this  chlorine-ion  possesses  the  same  properties 
exhibited  by  the  chlorine-ions  of  other  combinations  in  which 
it  is  contained,  hence,  in  all  soluble  metallic  chlorides.  These 
properties  of  the  chlorine-ion,  however,  differ,  entirely  from 
those  of  chlorine  in  the  ordinary  elementary  state,  it  possess- 
ing neither  its  odor  nor  color ;  it  exists  only  in  solution  and 
has  not  the  bleaching  effect  of  chlorine  gas. 

These  totally  different  properties  thus  clearly  indicate  that 
the  ions  have  to  be  considered  as  modifications  of  the  elements 
designated  by  the  same  name,  or  that  the  ions  have  to  be 
thought  of  as  existing  in  a  condition  different  from  the  elementary 
one ;  and  the  reason  for  these  different  conditions  and  prop- 
erties will  be  more  accurately  'known  after  we  have  to  some 
extent  become  acquainted  with  the 

Theory  of  solutions.  A  solution  is  not  a  mere  mechanical 
mixture  of  an  invisible,  finely  divided  solid  body  with  the 
solvent,  but  by  solution  in  a  solvent  a  body  partially  loses  its 
characteristic  properties  and  acquires  new  ones,  and  the  dis- 
solving process  may  be  viewed  as  a  chemical  process  in  so  far 
as  changes  of  energy  (see  later  on),  for  instance,  fixation  or 
disengagement  of  heat,  are  connected  with  it. 

There  are  not  only  solutions  of  solid  substances  in  liquids, 
'but  also  solutions  of  liquids  in  liquids,  of  gases  in  liquids,  and 
of  gases  in  gases.  However,  the  last-mentioned  solutions  are 
of  interest  to  us  only  in  so  far  as  it  has  been  shown  that  the 
laws  which  they  follow  are  also  valid  for  solutions  of  solid 
bodies  in  liquids.  For  the  proof  of  this  we  are  indebted  to 
van't  Hoff. 


MAGNETISM    AND    ELECTRICITY.  49 

If  a  layer  of  a  dilute,  pale  blue  cupric  sulphate  solution  be 
•carefully  brought,  so  as  to  avoid  mixing,  upon  a  concentrated 
•cupric  sulphate  solution  of  a  vivid  blue  color,  and  the  vessel 
containing  the  solutions  be  allowed  to  stand  quietly,  it  will  be 
noticed  that  the  pale  blue  solution  gradually  acquires  a  more 
intense  blue  color,  while  the  concentrated  solution  becomes 
paler.  The  molecules  of  the  cupric  sulphate  diffuse  from  the 
stronger,  into  the  weaker  solution  until  the  liquid  has  ac- 
quired a  uniform  concentration. 

This  phenomenon  is  based  upon  the  same  law  followed  by 
"the  gases.  A  gas  endeavors,  when  occasion  is  offered,  to 
occupy  a  larger  space ;  the  energy  of  motion  (kinetic  energy) 
inherent  in  the  individual  gas  molecules  propels  them  until 
their  motion  is  stopped  by  the  walls  of  the  enlarged  space. 
The  molecules  in  the  cupric  sulphate  solution  possess  a  similar 
•energy  of  motion  and  by  it,  as  we  have  seen,  are  forced  from 
the  concentrated,  into  the  weak  solution.  This  force,  which 
corresponds  to  the  gas  pressure,  is  called 

Osmotic  pressure.  Its  presence  can  readily  be  demonstrated 
by  the  following  experiment :  Fill  a  glass-cylinder  with  satur- 
ated sugar  solution,  close  the  cylinder  air-tight  with  a  semi- 
permeable  bladder,  and  place  it  upright  in  a  vessel  filled  with 
water  so  that  the  latter  stands  a  few  centimeters  above  the 
bladder ;  the  bladder  bulges  up  in  a  short  time.  This  pheno- 
menon is  caused  by  the  effort  of  the  sugar  molecules  to  diffuse 
into  the  surrounding  water,  being,  however,  prevented  from 
doing  so  by  the  bladder,  while  water  molecules  penetrate 
through  the  bladder  into  the  cylinder.  If  the  cylinder  be  re- 
moved from  the  water  and  the  bladder  be  punctured  with  a 
pin,  the  pressure  which  had  existed  becomes  plainly  percepti- 
ble by  a  jet  of  fluid  being  forced  upward.  By  exact  investiga- 
tions of  the  magnitude  of  osmotic  pressure  it  has  been  ascer- 
tained that  it  is  proportioned  to  the  number  of  molecules 
dissolved  in  the  unit  volume,  and  that  the  temperature  has 
the  same  effect  upon  osmotic  pressure  as  upon  gases,  conformity 
with  the  laws  valid  for  gases  being  thus  proved.  According 
4 


50  ELECTRO-DEPOSITION    OF    METALS. 

to  Avogadro's  law  equal  volumes  of  different  gases  under  the 
same  conditions  of  temperature  and  pressure  contain  equal 
numbers  of  molecules,  and  the  weights  of  these  gases  are  thus 
in  the  same  ratio  as  their  respective  molecular  weights. 

Solutions,  as  has  been  proved  by  van't  Hoff,  follow  the  same 
law  and,  according  to  van't  Hoff,  the  law  applied  to  them  is 
expressed  as  follows :  Solutions  which  contain  an  equal  num- 
ber of  dissolved  molecules  in  the  same  volume  of  solvent 
(equimolecular  solutions)  exert,  under  the  same  conditions  of 
temperature,  the  same  osmotic  pressure  which  has  the  same 
value  as  the  gas-pressure  these  bodies,  if  in  a  gaseous  state, 
would  under  the  same  conditions  of  temperature  exert  in  a 
volume  of  gas  equal  to  the  volume  of  solvent. 

It  should,  however,  be  borne  in  mind  that  the  osmotic  laws 
are  valid  only  for  dilute  solutions,  just  as  the  gas-laws  hold 
good  only  for  dilute  gases. 

Electrolytic  dissociation.  Clausius  originated  the  idea  that 
the  molecules  of  an  electrolyte  are  dissociated  to  molecular 
particles  corresponding  to  our  ions.  He  supposed  that  the 
molecules  are  in  constant  motion  whereby  they  are  partially  de- 
composed, and  that  the  molecular  particles  formed  again  attract 
the  molecular  particles  of  opposite  names  of  the  non-decom- 
posed aggregate  molecules,  and  thus  effect  the  dissociation  of 
the  latter.  On  the  other  hand,  molecular  particles  of  opposite 
names  will  again  form,  under  favorable  conditions,  aggregate 
molecules.  However,  as  soon  as  a  current  passes  through  the 
electrolyte,  the  irregular  and  changing  movements  of  the 
molecular  particles  will  cease,  and  they  will  take  the  direc- 
tion presented  by  the  action  of  the  current,  i.  e.t  the  positive 
molecular  particles  will  wander  with  the  direction  of  the  cur- 
rent to  the  cathode,  and  the  negative  ones  to  the  anode. 

The  method,  discovered  by  Raoult,  of  determining  the  mole- 
cular weights  of  dissolved  bodies  from  the  elevation  of  the 
boiling  point  and  the  depression  of  the  freezing  point,  caused, 
in  connection  with  van't  Hoff's  osmotic  laws,  a  further  investi- 
gation of  the  dissociation  of  electrolytes.  It  was  known  thai 


MAGNETISM    AND    ELECTRICITY.  51 

salt  solutions  possess  a  higher  boiling  point  than  the  pure 
solvent.  Further  investigations  proved  the  elevation  of  the 
boiling  point  to  be  proportional  to  the  number  of  the  dissolved 
molecules,  and  that  equimolecular  solutions,  i.  e.,  solutions 
which  contain  an  equal  number  of  dissolved  molecules  in  the 
same  volume  of  solvent,  show  the  same  elevation  of  the  boil- 
ing point.  On  the  other  hand,  the  freezing  point  of  solutions 
is  lowered  in  proportion  to  the  dissolved  molecules,  and  equi- 
molecular solutions  show  the  same  depression  of  the  freezing 
point. 

However,  not  all  substances  in  equimolecular  solutions 
furnished  at  the  same  temperature,  the  same  osmotic  pressure 
as  sugar  solutions  or  solutions  of  other  organic  bodies.  Thus, 
solutions  of  acids,  bases,  and  salts  yielded  too  high  an  osmotic 
pressure,  and  also  showed  deviations  in  so  far  that,  as  com- 
pared with  equimolecular  solutions  of  many  organic  sub- 
stances, they  caused  under  entirely  equal  conditions,  a  higher 
elevation  of  the  boiling  point  or  depression  of  the  freezing 
point.  Since,  as  regards  gas-pressure,  some  gases  also  do  not 
follow  Avogadro's  law,  and  these  exceptions  were  explained 
by  assuming  that  the  molecules  decompose  to  molecular 
particles,  the  same  assumption  was  made  for  solutions  of  acids, 
bases  and  salts. 

S.  Arrhenius,  in  1887,  found  that  all  the  solutions  which 
formed  exceptions  to  the  osmotic  law  and  showed  deviating 
results  as  regards  elevation  of  the  boiling  point  and  depression 
of  the  freezing  point,  possessed  the  common  property  of  con- 
ducting the  electric  current,  while  solutions  of  organic  bodies 
which,  as  above  mentioned,  followed  the  laws  referred  to,  were 
non-conductors  of  the  electric  current.  Arrhenius  ascertained 
that  very  considerable  exceptions  appear  for  water  as  solvent, 
since  the  pressure  is  greater  than  van't  Hoft's  law  requires, 
and  it  would  therefore  be  but  natural  to  suppose  that  sub- 
stances which  give  too  large  pressures  in  aqueous  solutions  are 
dissociated.  He  further  found  that  dissociation  increases  with 
increasing  dilution,  and  he  established  the  law  that  for  every 


52  ELECTRO-DEPOSITION    OF    METALS. 

dilute  solution  the  ratio  of  dissociation  is  equal  to  the  ratio  of 
molecular  conductivity  present  to  the  conductivity  of  infinite 
dilution,  i.  e.,  to  the  maximum  of  molecular  conductivity.  The 
independent  particles  of  the  molecules  formed  are  the  ions. 

It  further  follows  that  it  is  the  ions  which  take  charge  of  the 
progressive  motion  of  the  current  because  only  ion-forming 
solutions  are  capable  of  conducting  the  current.  The  ions 
are  supposed  to  be  charged  with  a  certain  quantity  of  electricity 
— the  cations  with  positive,  the  anions  with  negative,  electricity 
— and  so  long  as  no  current  passes  through  the  electrolyte, 
they  move  free  in  the  latter.  However,  when  a  current  is 
conducted  through  the  electrolyte,  the  ions  are  attracted  by 
the  electrodes,  the  positively  charged  cations  by  the  negatively 
charged  cathode,  and  the  negatively  charged  anions  by  the 
positively  charged  anode.  By  reason7  of  the  movements  of  the 
ions  to  the  electrodes  this  phenomenon  may  be  called  migration 
of  the  ions. 

The  ions  on  reaching  the  electrodes  are  freed  of  their  charge, 
i.  e.,  they  yield  their  electricity  to  the  electrodes,  but  they  lose 
thereby  their  ion-nature  and  are  changed  into  their  respective 
elementary  atoms  ;  they  show  no  longer  the  properties  of  ions 
but  those  of  the  ordinary  elements.  As  is  well-known  the 
various  modifications  of  carbon  (diamond,  graphite)  are  chem- 
ically alike,  namely  in  all  cases  carbon,  but  they  have  entirely 
different  properties,  the  latter  be-ing  conditional  on  an  entirely 
different  content  of  energy. 

Energy.  By  energy  is  understood  the  work  and  everything 
which  can  be  the  result  from  work,  and  be  again  converted  into 
work.  A  distinction  is  made  between  various  kinds  of  work. 
The  effect  of  mechanical  work  expresses  itself  through  the  pro- 
duct of  force  and  motion,  i.  e.,  the  force  required  to  convey  a 
body  a  certain  distance.  If  we  push  a  wagon,  the  force  with 
which  we  push  against  the  wagon  multiplied  by  the  motion, 
i.  e.,  the  distance  the  wagon  has  been  pushed,  is  the  value  of 
the  work. 

Now  a  distinction  has  to  be  made  between  the  force  with 


MAGNETISM    AND    ELECTRICITY.  53 

which  a  man  in  pushing  presses  against  the  wagon,  and  that 
with  which  the  wagon  presses  against  the  man,  who  does  the 
pushing.  In  comparison  we  speak  of  both  forces  as  force  and 
counter-force,  and  physics  teaches  us  that  force  and  counter- 
force  are,  in  all  cases,  of  the  same  magnitude,  but  exerted  in 
opposite  directions.  Both  these  propositions  may  be  com- 
bined to  the  proposition  of  the  conservation  of  force  and  work, 
which  reads  :  No  quantity  of  force  and  no  quantity  of  work  are 
lost;  the  force  and  work  consumed  are  always  again  met  with 
in  another  definite  form. 

When  a  wagon  has  been  pushed  to  a  higher  point  of  an 
oblique  plane,  it  has  taken  up  a  certain  quantity  of  work  cor- 
responding to  the  value  from  force  multiplied  by  motion  in 
the  direction  of  the  force.  It  possesses  a  certain  energy  which 
it  can  and  does  give  up  when  it  is  released  ;  the  wagon  runs 
down  the  oblique  plane,  and  the  velocity  with  which  it  runs 
down  is  also  a  form  of  energy. 

If  an  article  be  ground  upon  an  emery  wheel,  a  certain  fric- 
tional  work  is  performed  ;  the  article  becomes  warm  by  friction. 
Hence  the  heat  which  is  developed  is  another  form  of  energy 
of  the  frictional  work,  since  according  to  the  law  of  the  con- 
servation of  work  no  quantity  of  work  is  lost  in  nature. 

If  carbon  (C)  be  burnt  in  the  air,  carbonic  oxide  (C02)  is 
formed.  The  law  of  the  conservation  of  matter  teaches  us  that 
no  substance  is  lost,  and  hence  the  quantity  of  carbonic  acid 
which  has  been  formed  by  combustion  must  be  exactly  as 
large  as  the  quantities  of  carbon  and  oxygen  of  the  air  which 
existed  previous  to  combustion.  The  carbon  and  oxygen  of 
the  air  prior  to  their  union  to  carbonic  acid  possess  a  quantity 
of  work  or  energy  differing  from  that  after  union,  the  heat 
generated  by  the  combustion  being  a  manifestation  of  energy 
produced  in  a  chemical  way. 

Every  elemerit  has  to  be  thought  of  as  possessing  a  definite, 
inherent  content  of  energy  which,  when  the  element  enters 
into  combination  with  other  elements,  may,  and  generally 
does,  undergo  a  change.  Thus  in  entering  into  a  combination 


54  ELECTRO-DEPOSITION    OF    METALS. 

the  elements  yield  a  portion  of  their  content  of  energy,  gen- 
erally in  the  form  of  heat,  though  sometimes  also  with  lumin- 
ous phenomena,  so  that  the  content  of  energy  in  the  combina- 
tion is  less  than  the  content  of  energy  of  the  elements  before 
their  union.  If  now  a  solution  of  the  combination  in  water 
be  prepared,  a  change  in  the  content  of  energy  again  takes 
place  by  dissociation,  the  content  of  energy  present  in  the 
combination  being  partially  converted  into  electrical  energy. 
The  ions  appearing  thereby  receive  electrical  charges — the 
metal-ions  positive  charges  and  the  other  ions  negative  charges 
— and  the  nature  of  ions  may  be  characterized  by  saying,  they 
differ  from  the  elementary  atoms  of  similar  names  in  having 
a  different  content  of  energy. 

Processes  on  the  electrodes.  As  previously  mentioned,  in  the 
salts  all  the  metal-ions  are  positive  and  the  other  ions  of  the 
metal  combination — the  acid  residue — negative. 

The  ions  arriving  at  the  electrodes  possess  the  power  of 
entering  into  chemical  processes  with  the  constituents  of  the 
electrolyte  or  with  the  electrodes,  as  may  be  shown  by  the 
following  examples : 

When  a  solution  of  potassium  disulphate  (K2S04)  is  electro- 
lyzed  between  unassailable  platinum  electrodes,  the  following 
event  takes  place.  The  potassium -ions  migrate  to  the  cathode 
and  separate  metallic  potassium, 


Potassium  disulphate. 

which,  however,  as  is  well  known,  cannot  exist  in  water,  but 
immediately  forms  with  the  solvent  potassium  hydroxide 
(caustic  potash)  according  to  the  following  equation  : 

2K  +  2H20  =  2KOH    +    H2 

Potassium      Water.     Caustic  potash.     Hydrogen. 

That  this  transposition  takes  place  in  the  manner  described, 


MAGNETISM    AND    ELECTRICITY.  55 

is  shown  by  the  abundance  of  hydrogen  *  which  escapes  in 
the  electrolysis  of  the  potassium  disulphate.  On  the  other 
hand,  the  acid  residue  S04  migrates  to  the  anode,  which,  as  it 
•consists  of  insoluble  platinum,  cannot  saturate  the  acid  residue, 
and  the  latter  is  also  transposed  with  water  according  to  the 
following  equation : 

S04        +        H20       =    H2S04     +     0 

Sulphuric  acid  residue.      Water.       Sulphuric  acid.       Oxygen. 

The  oxygen  escapes,  and  the  sulphuric  acid  formed  combines 
again  to  potassium  disulphate  with  the  caustic  soda  formed 
on  the  cathode. 

A  like  liberation  of  oxygen  takes  place  when  very  dilute 
hydrochloric  acid  f  is  electrolyzed  with  platinum  anodes. 
Hydrogen  escapes  on  the  cathode,  but  no  chlorine  appears  on 
the  anode,  an  equivalent  quantity  of  oxygen  being,  however, 
liberated.  The  water  is  decomposed  by  the  chlorine,  hydrogen 
chloride  and  oxygen  being  formed  according  to  the  following 
•equation  : 

C12    +    2H20    =      4HC1      +      02 

Chlorine.         Water.         Hydrogen  chloride.     Oxygen. 

The  oxygen  appearing  in  both  cases,  as  well,  as  the  hydrogen 
appearing  in  the  first-mentioned  example,  are  called  secondary 
products  of  electrolysis,  because  the  products  first  separated 
under  the  given  conditions  could  not  exist  and,  in  being  de- 
composed or  transposed,  formed  together  with  the  solvent  the 
above-mentioned  products. 

When  sodium  hydroxide  (caustic  soda)  is  electrolyzed, 
hydrogen  appears  on  the  cathode,  because  sodium,  like  potas- 

*This  explanation  is  here  retained,  though  based  upon  potential  measurements, 
it  may,  according  to  Le  Blanc,  be  supposed  that  the  hydrogen  separates  primarily 
and  originates  from  the  hydrogen-ions  of  the  dissociated  water  of  the  solution. 

t  The  process  does  not  pass  off  as  smoothly  as  represented  by  the  formula,  but 
the  example  is  given  as  an  illustration  according  to  Ostwald's  "Grundlinien  der 
Chemie,"  I.  p.  203. 


56  ELECTRO-DEPOSITION    OF    METALS. 

slum  in  the  former  example,  cannot  exist  with  water,  and 
sodium  hydroxide  is  again  formed,  hydrogen  being  at  the  same 
time  liberated.  The  hydrogen-ion  which  also  cannot  exist  by 
itself,  is  discharged  on  the  anode,  water  and  oxygen  being 
formed  according  to  the  following  equation  : 

40H  =  2H20  +  02 

Hydroxide.       Water,        Oxygen. 

Let  us  now  turn  to  the  other  cases  in  which  the  ions,  sepa- 
rated on  the  electrodes,  enter  with  the  latter  into  chemical 
processes. 

A  solution  of  cupric  sulphate  (blue  vitriol)  CuS04  is  to  be 
electrolyzed.  The  copper  ions  migrate  to  the  cathode 

£-Cu  |  S04-> 

Cupric  sulphate. 

and  deposit  their  copper  in  the  form  of  a  galvanic  deposit,  the 
acid  residue — the  anion — migrating  to  the  anode.  If  the 
latter  consists  of  a  soluble  metal,  for  instance,  copper,  the  acid 
residue  becomes  saturated  with  copper,  dissolving  approx- 
imately the  same  quantity  of  it  as  has  been  deposited  upon 
the  cathode.  Theoretically  the  quantity  dissolved  from  the 
anode  by  the  acid  residue  should  exactly  correspond  to  the 
quantity  of  metal  separated  on  the  cathode.  However,  in 
practice,  such  is  not  the  case,  because  the  acid  residue  is  partly 
subject  to  other  decompositions,  especially  the  formation  of 
H2S04,  oxygen  being  at  the  same  time  separated. 

All  other  processes  in  which  metallic  anodes  capable  of  solu- 
tion by  the  acid  residue  are  used,  run  their  course  in  a  manner 
similar  to  the  electrolysis  of  blue  vitriol. 

As  previously  mentioned,  secondary  products  may  be  liber- 
ated by  electrolysis.  The  separation  of  metal  on  the  cathode 
may  also  be  effected  in  a  secondary  manner,  and  in  galvanic 
processes  this  is  mostly  brought  about  on  purpose.  Referring 
to  the  previously  mentioned  example  of  the  electrolysis  of  blue- 


MAGNETISM    AND    ELECTRICITY.  57 

vitriol,  the  copper  could  only  be  separated  in  a  primary  man- 
ner ;  by  adding,  however,  a  small  quantity  of  sulphuric  acid 
to  the  blue  vitriol  solution,  separation  of  copper  in  a  secondary 
manner  takes  place.  The  sulphuric  acid  being  in  a  diluted 
state  is  more  strongly  dissociated  than  the  blue  vitriol  solution, 
the  ions  of  sulphuric  acid — hydrogen  and  acid  residue  S04 — 
first  of  all  taking  charge  of  the  conduction  of  the  current,  and 
the  hydrogen-ions  separate  the  copper  on  the  cathode  accord- 
ing to  the  following  equation  : 

CuS04     -|-     H2     =     Cu     '+     H2S04 

Cupric  sulphate.     Hydrogen.       Copper.       Sulphuric  acid. 

In  the  electrolysis  of  a  silver  bath  containing  potassium- 
silver  cyanide  (KAgCN2),  potassium-ions  and  silver  cyanide- 
ions  (AgCN2*)  appear : 

(a)  __  |  ^_K  |  AgCN2->  |  + 

From  the  solution  of  potassium-silver  cyanide  the  potas- 
sium-ions separate  secondarily  metallic  silver  on  the  cathode, 
potassium  cyanide  being  formed  according  to  the  following 
equation : 

(6)  K         +         KAgCN2  Ag  +  2KCN. 

Potassium-ion.       Potassium  silver  cyanide.       Silver  potassium  cyanide. 

The  anions  AgCN2  migrate  to  the  anode,  are  there  decom- 
posed to  silver  cyanide  (AgCN)  and  cyanogen  (CN),  the 
cyanogen-ions  dissolve  from  the  anode  silver,  silver  cyanide 
being  formed,  and  2  silver  cyanide  atoms  combine  with  the 
above  (in  b)  liberated  2  potassium  cyanide,  to  2  potassium, 
silver  cyanide  atoms : 

(c)Ag       +       CN       =      AgCN 

Silver.  Cyanogen.  Silver  cyanide. 

(d)  2AgCN     '  +       2KCN  2KAgCN2 

Silver  cyanide.  Potassium  cyanide.         Potassium  silver  cyanide. 

"Hittorf,  Ostwald's  Klassiker,  23,  §  45. 


•58 


ELECTRO-DEPOSITION    OF    METALS. 


The  quantities  of  substances  separated  from  the  electrolytes 
by  the  electric  current  are  subject  to  fixed  laws,  which,  after 
their  discoverer,  are  named 

Laws  of  Faraday.  These  laws  are  followed  by  both  the 
primary,  as  well  as  secondary  products  of  electrolysis,  because 
the  latter  are  produced  by  primary  separations,  the  secondary 
being  proportional  and  chemically  equivalent  to  them.  The 
first  of  these  laws  is  as  follows : 

The  quantity  of  substances  which  is  liberated  on  the  electrodes 
is  directly  proportional  to  the  strength  of  the  electric  current  which 
has  been  conducted  through  the  electrolytes,  and  the  time. 


FIG.  7. 


By  conducting  the  current  through  a  closed  decomposing 
cell,  Fig.  7,  filled  with  acidulated  water  and  furnished  with 
two  platinum  electrodes  which  are  connected  with  the  poles 
of  a  source  of  current,  oxygen  is  evolved  on  the  positive  elec- 
trode, and  hydrogen  on  the  negative  electrode.  If  the  gas- 
mixture  (oxyhydrogen  gas)  which  is  evolved  be  caught  under 
water  in  a  graduated  tube,  the  quantity  of  oxyhydrogen  gas 


MAGNETISM    AND    ELECTRICITY. 


59 


produced  by  a  current  of  fixed  strength  within  a  determined 
time  can  be  readily  ascertained.  If  now  a  current  of  double 
the  strength  be  for  the  same  length  of  time  passed  through 
the  decomposing  cell,  the  quantity  of  oxyhydrogen  gas  pro- 
duced will  be  found  twice  as  large  as  in  the  first  case. 

Faraday  allowed  the  same  quantity  of  current  to  pass 
through  a  series  of  decomposing  cells,  coupled  one  after  an- 
other, which  contained  electrolytes  of  different  compositions, 
and  determined  quantitatively  the  separations  of  cations 
effected  in  the  various  cells  by  an  equal  quantity  of  current. 
Suppose  the  first  cell  to  be  a  water-decomposing  cell  like  Fig. 
7,  let  the  second  cell  contain  potassium  silver  cyanide  solu- 
tion with  a  slight  excess  of  potassium  cyanide,  the  third  cell 
an  acidulated  solution  of  cupric  sulphate,  and  the  fourth  cell 
a  solution  of  cuprous  chloride  in  hydrochloric  acid. 

When  electrolysis  has  been  carried  on  for  half  an  hour,  the 
current  is  interrupted,  and  the  quantity  of  hydrogen  calculated 
from  the  measured  quantity  of  oxyhydrogen  gas  produced. 
The  platinum  cathodes,  the  weight  of  which  has  been  deter- 
mined previous  to  electrolysis,  are  rinsed  in  water,  next  in 
alcohol,  and  finally  in  ether.  They  are  then  thoroughly  dried 
and  again  weighed  to  determine  the  quantities  of  metal  sepa- 
rated in  the  individual  cells.  The  following  quantities  were 
found : 


Electrolyte.' 

I. 

Dilute 
sulphuric  acid 
1:15. 

II. 

Potassium 
silver  cyanide 
KAgCy2. 

III. 
Cupric 
sulphate 
CuSO4. 

IV. 

Cuprous 
chloride 
CuCl. 

Quantity  of  sepa-  / 
rated  cations.  .  \ 

67  ccm.  H  = 
6.00  mg.  H 

650  mg.  Ag. 

190  mg.  Cu 

380  mg.  .Cu 

For  1  mg.   H  are 
separated    .    .    . 

1  mg.  H 

108.33  mg.  Ag. 

31.66  mg.  Cu 

63.3  mg.  Cu 

Atomic  weights.    . 

1 

108 

63.3 

63.3 

60  ELECTRO-DEPOSITION    OF    METALS. 

From  this  it  follows  that  the  separated  quantities  of  cations, 
referred  to  one  part  by  weight  of  hydrogen,  represent  almost 
exactly  the  quantities  of  metals  which  correspond  to  a  single 
valence  of  their  atomic  weights.  In  the  electrolytes  II  and  IV, 
the  silver  atoms  and  copper  atoms  are  univalent,  and  in  elec- 
trolyte III,  bivalent.  Hence,  in  II  and  IV  were  separated  the 
quantities  of  metal,  108.33  mg.  silver  (error  in  per  cent.  0.33) 
and  63.3  mg.  copper,  which  corresponds  to  the  univalence  of 
the  atoms,  and  in  III  only  a  valence  amounting  to  31.56  mg. 
copper  which  corresponds  to  the  bivalence  of  the  copper  atoms 
in  cupric  sulphate. 

Hence  the  second  law  of  Faraday,  as  expressed  by  v.  Helm- 
holtz,  reads  as  follows  :  The  same  quantity  of  current  liberates 
in  the  different  electrolytes  an  equal  number  of  valences  or  converts 
them  into  other  combinations. 

It  has  previously  been  mentioned  that  for  the  development 
of  1  g.  hydrogen,  96540  coulombs  must  pass  through  the 
electrolyte.  According  to  determinations  by  F.  and  W.  Kohl- 
rausch,  0.3290  mg.  copper  is  liberated  from  cupric  salts  by  a 
quantity  of  1  coulomb,  or  31.65  g.  by  96540  coulombs.  This 
quantity  of  current  is  the 

Electro-chemical  equivalent,  i.  e.,  the  number  of  coulombs 
which  split  off  in  one  second  the  portion  of  atomic  weights  of 
the  cations  (metals)  or  of  the  anions  referred  to  a  valence  and 
expressed  in  grammes,  i.  e.,  the  gramme-equivalent.  Hence, 
for  the  separation  of  1  gramme-equivalent  of  copper  =  31.65, 
or  of  1  gramme-equivalent  of  silver  =  108i96540  coulombs  are 
always  required. 

From  the  laws  of  Faraday  results  the  view  previously  re- 
ferred to,  that  the  passage  of  the  current  through  the  electro- 
lyte is  confined  to  the  simultaneous  movement  of  the  ions,  and 
that  no  current  can  pass  through  the  electrolyte  if  the  ions  be 
wanting.  Hence  the  ions  of  the  electrolyte  are  charged  or 
combined  with  specified  quantities  of  electricity,  and  one  por- 
tion of  Faraday's  law  may,  according  to  Ostwald,  be  thus  ex- 
pressed :  The  quantities  of  the  different  ions  combined  with  equal 


MAGNETISM    AND    ELECTRICITY. 


61 


quantities  of  electricity  are  proportional  to  the  combining  weights 
of  these  ions,  and  the  entire  law  may  be  summed  up  as  follows  : 
In  the  electrolytes  the  electricity  moves  only  simultaneously  with 
the  constituents  of  the  electrolytes  which  are  the  ions.  The  moved 
quantities  of  electricity  are  proportional  to  the  quantities  of  ions, 
and  amount  to  9654*0  coulombs,  or  a  multiple  of  them,  for  one 
molecule  of  any  one  ion. 

Below  is  given  a  table,  of  the  electro-chemical  equivalents, 
and  from  them  will  be  calculated,  in  the  practical  part  of  the 
work,  the  time  required  for  the  formation  of  deposits  of  a  cer- 
tain specified  weight,  the  current-strength  required  for  the 
purpose,  etc.  The  specific  gravities  of  metals,  which  are  also 
required  for  the  above-mentioned  calculations,  have  been  added 
to  the  table. 


Electro-chemical 
Equivalent. 

Deposit  in 
1  Ampere-hour 

Specific 
Gravity. 

Hydrogen  
Antimony  

0.104 
0.415 

0.0375 
1.4940 

0.00009 
6  8 

Arsenic  
Cobalt 

0.258 
0  305 

0.9322 
1  1001 

5.7 
8  7 

Copper  from  cupric  salts  .    .    . 
Copper  from  cuprous  salts    .    . 
Gold  from  auric  salts  ' 
Gold  from  aurous  salts  .... 
Iron  from  ferric  salts      •    .    . 

0.329 
0.658 
0.681 
2.043 
0.193 

1.1858 
2.3717 
2.4513 
7.3560 
0  6950 

8.8 
8.8 
19.2 
19.2 

7  8 

Iron  from  ferrous  salts  .... 
Lead                 

0.289 
1  071 

1.0423 
3  8580 

7.8 
11  3 

Nickel       

0.304 

1.0945 

8  6 

0.504 

1.8160 

21  4 

Silver        

1.118 

4.0248 

10  5 

Tin  from  stannic  salts    .... 
Tin  from  stannous  salts  .... 
Zinc    

0.308 
0.616 
0.339 

1.1094 
2.2180 
1.2200 

7.3 
7.3 

7.2 

Solution-tension  of  metals.  A  fluid  evaporates  on  the  surface 
until  the  vapor-pressure  produced  is  equal  to  the  evaporation- 
tension  of  the  fluid.  Analogous  to  this  process  is  the  osmotic 
pressure  which  a  salt  exercises  when  dissolved  in  water,  a 
pressure  which  increases  with  the  quantity  of  the  salt  until  it 


62  ELECTRO-DEPOSITION    OF    METALS. 

is  in  equilibrium  with  the  solution-tension.  According  to 
Nernst,  every  metal  when  immersed  in  an  electrolyte  also 
possesses  the  power  conditional  to  its  chemical  nature  to  give 
off  metal  atoms  as  ions  (cations)  to  the  solution,  and  this 
power  is  called  solution-tension. 

The  solution-tension"  is  the  greater  the  smaller  the  number 
of  cations  which  are  already  present  in  the  electrolyte;  if,  on 
the  other  hand,  the  electrolyte  contains  a  great  number  of 
cations  derived  from  the  dissociation  of  the  salt,  the  osmotic 
pressure  may  overbalance  the  solution-tension,  or  the  osmotic 
pressure  may  be  equal  to  the  solution-tension. 

In  the  first  case,  when  the  solution-tension  preponderates, 
the  metal  will  give  up  to  the  solution  cations  charged  with 
positive  electricity,  while  an  equally  large  quantity  of  negative 
electricity  remains  in  the  metal.  Suppose  zinc  dipping  in 
water,  then  the  zinc-ions  passing  into  solution  will  be  charged 
with  positive  electricity,  while  the  metal  is  charged  with  an 
equally  large  quantity  of  negative  electricity. 

If  the  water  Be  replaced  by  a  solution  of  zinc  sulphate 
(white  vitriol)  which,  in  consequence  of  dissociation,  already 
contains  a  larger  number  of  positive  zinc-ions  and  negative 
acid-residue-ions,  additional  positive  zinc-ions  will  be  given 
up  to  the  solution  by  the  zinc  so  long  as  the  solution-tension 
of  the  zinc  overbalances  the  osmotic  pressure  of  the  dissolved 
zinc-ions.  When  an  equilibrium  between  osmotic  pressure 
and  solution-tension  is  reached,  the  further  formation  of  zinc- 
ions  ceases. 

If  the  more  electro-negative  copper  be  dipped  in  water  it 
also  makes  an  effort  to  ionize,  i.  e.,  to  give  up  to  the  solution 
copper-ions  charged  with  positive  electricity.  If,  however,  the 
water  be  replaced  by  cupric  sulphate  solution,  it  happens  that 
the  osmotic  pressure  of  copper-ions  formed  by  dissociation  of 
the  electrolyte  is  greater  than  the  solution-tension  of  the  cop- 
per, and  hence  not  only  counteracts  the  formation  of  new 
copper-ions,  but  carries  positive  copper-ions  from  the  electro- 
lyte to  the  copper,  the  latter  receiving  thereby  a  positive 


MAGNETISM    AND    ELECTRICITY.  6$ 

charge,  while  the  fluid  surrounding  the  copper  becomes 
negative. 

However,  no  matter  whether  the  solution-tension  may  con- 
siderably overbalance  the  osmotic  pressure,  by  the  mere  dip- 
ping of  the  metal  in  the  electrolyte  the  quantity  of  ions  which 
are  newly  formed  will  always  be  small,  because  by  reason  of 
the  electrostatic  attraction  of  the  cations  by  the  negatively- 
charged  metal,  there  will  take  place  on  the  contact-surface 
between  the  metal  and  the  electrolyte  an  accumulation  of 
cations,  the  osmotic  pressure  of  which  will  consequently  be 
increased,  and  counteract  the  solution-tension.  The  latter 
can  only  become  again  active,  when  the  free  electricities  are 
conducted  away  by  a  closed  circuit,  as  will  be  explained  in 
the  next  section. 

Osmotic  theory  of  the  production  of  the  current,  according  to 
Nernst.  The  behavior  of  zinc  in  a  zinc  sulphate  solution,  and 
that  of  copper  in  a  cupric  sulphate  solution,  has  above  been 
referred  to.  If  a  cell  be  put  together  of  zinc  dipping  in  zinc 
sulphate  solution,  and  copper  in  cupric  sulphate  solution,  such 
as  a  Daniell  cell,  in  which  the  two  solutions  are  separated  by 
a  porous  partition,  called  a  diaphragm,  the  following  processes 
take  place : 

From  the  zinc,  positive  zinc-ions  pass  into  solution  so  long 
as  the,  at  first,  slighter  osmotic  pressure  of  the  electrolyte 
balances  the  solution-tension  ;  the  zinc  becomes  negatively 
electric  and  the  electrolyte  positively  electric  on  the  contact- 
surface.  By  the  preponderance  of  the  osmotic  pressure  of  the 
copper  sulphate  solution  over  the  solution-tension  of  the 
copper,  positive  copper-ions  are  separated  on  the  copper,  and 
yield  their  positive  charges  to  the  latter.  They  themselves  are 
transformed  from  the  ion  state  into  the  molecular  state,  thus 
becoming  non-electric,  while  on  the  contact-surface  the  cupric 
sulphate  solution  becomes  negatively  electric.  Hence  a  state 
of  rest  supervenes,  in  which  the  zinc  is  charged  with  negative, 
and  the  copper  with  positive,  electricity,  while  the  zinc  solution 
is  charged  positively  and  the  copper  solution  negatively.  If 


64  ELECTRO-DEPOSITION    OF    METALS. 

now  by  means  of  a  metallic  wire  the  zinc  be  outside  of  the 
solutions  connected  with  the  copper,  thus,  establishing  a  closed 
circuit,  the  following  process  takes  place  :  The  positive  elec- 
tricity in  the  copper  migrates  through  the  wire  to  the  zinc, 
and  neutralizes  the  quantity  of  negative  electricity  present  in 
the  latter.  By  the  flow  of  positive  electricity  from  the  copper 
the  state  of  equilibrium,  which  existed  between  copper  and 
cupric  sulphate,  is  disturbed,  and  the  osmotic  power  being  now 
predominant,  the  solution  again  gives  up  copper-ions  to  the 
copper,  whereby  the  latter  is  again  charged  with  positive 
electricity.  On  the  other  hand,  after  the  exchange  of  elec- 
tricities in  the  zinc  by  the  solution-tension,  fresh  zinc-ions  can 
be  brought  into  solution.  Thus  a  current  flows  continuously 
from  copper  to  zinc  until  either  no  more  copper-ions  are 
conveyed  from  the  cupric  -sulphate  solution  to  the  copper,  or 
until  all  the  zinc  is  ionized,  i.  e.t  dissolved. 

Nernst's  conception  of  the  solution-tension  of  the  metals  is 
analogous  to  that  of  the  osmotic  pressure,  the  impelling  force 
of  a  Daniell  battery  having  the  character  of  a  pressure,  and 
for  that  reason  Ostwald  designates  a  galvanic  battery  as  a 
machine  driven  by  osmotic  pressure,  eventually  by  electrolytic 
solution-tension. 

The  electro-motive  force  of  such  a  cell  is  mainly  determined 
by  the  magnitude  of  the  solution-tension  of  the  metals.  In 
the  closed  cell  the  metal  gives  up  with  greater  solution-tension 
its  atoms  as  ions  into  the  electrolyte  in  which  it  is  confined, 
while  the  cations  of  the  other  electrolyte  are  discharged 
on  the  metal  contiguous  to  it  and  pass  into  the  molecule  state. 
By  this,  the  dissolving  metal,  to  which  the  anions  of  the  other 
electrolyte — the  acid  residue — migrate,  becomes  the  anode,  and 
the  other  metal  on  which  the  cations  of  its  electrolyte  separate 
non-electrically,  the  cathode.  Since  the  cations  are  discharged 
on  the  cathode,  the  latter  is  also  called  the  conducting  elec- 
trode, and  the  anode  which  dissolves,  the  dissolving  electrode.' 

From  what  has  been  said,  it  might  appear  that  the  current 
dn  a  Daniell  cell  owes  its  existence  to  purely  physical  forces. 


MAGNETISM    AND    ELECTRICITY.  65 

The  solution-tension  of  the  metals  depends,  however,  on  their 
chemical  affinity,  and  the  current  is  actually  electric  energy 
which  has  been  formed  from  chemical  energy.  The  solution 
of  the  anode-metal  is  a  chemical  process,  whereby  the  cations 
are  forced  from  the  electrolyte  surrounding  the  anode ;  the 
anode-metal  endeavors  to  expand,  and  hence  the  mode  of 
action  of  chemical  affinity  in  converting  chemical  into  electric 
-energy  may  be  designated  as  the  effect  of  pressure. 

However,  additional  chemical  processes  take  place  in  the 
Daniell  cell ;  the  zinc  dissolves  to  zinc  sulphate  because  the 
unions  of  the  cupric  sulphate  solution  migrate  to  the  zinc, 
while  from  this  solution  a  quantity  of  copper  equivalent  to 
the  dissolved  zinc  is  deposited  on  the  cathode.  By  the  anion 
•SO 4  of  the  cupric  sulphate  solution  an  oxidation  of  the  zinc 
takes  place,  the  latter  acting  therefore  as  a  reducing  agent. 
The  cupric  sulphate  solution,  on  the  other  hand,  is  reduced  to 
copper,  and  the  acid-residue  S04  being  liberated  thereby  acts 
as  an  oxidizing  agent,  while  the  copper  of  the  cathode  remains 
chemically  unchanged.  Since,  according  to  Ostwald,  in  every 
chemical  process  which  takes  place  between  an  oxidizing  and 
a  reducing  agent,  variations  appear  in  the  ion-charges  by 
reason  of  the  varying  capacities  of  the  ions  to  absorb  or  dis- 
charge more  quantities  of  electricity,  such  cells  are  also  called 
oxidizing  and  reducing  cells.  Concentration  cells  will  later  on 
be  referred  to. 

Polarization.  By  polarization  is  understood  the  appearance 
•of  a  counter-current  passing  in  a  direction  opposite  to  that  of 
the  current  conducted  into  an  electrolyte ;  the  main  current  is 
therefore  weakened  by  this  counter-current.  Polarization 
takes  place  when  the  current  produces  substantial  changes  in 
the  electrolytes  or  on  the  electrodes,  no  matter  whether  such 
-changes  consist  in  a  difference  of  the  nascent  concehtrations  of 
the  electrolyte,  or  in  the  formation  of  gas-cells  by  the  separa- 
tion of  layers  of  gas  on  the  electrodes,  etc. 

If  a  weak  current  be  conducted  into  a  cell  filled  with  stand- 
ard cupric  sulphate  solution,  both  electrodes  of  which  consist 
5 


66  ELECTRO-DEPOSITION    OF    METALS* 

of  copper,  and  a  galvanometer  be  placed  in  the  circuit,  it  willl 
be  noticed  that  an  electrolytic  decomposition  takes  place.  The 
copper-ions  discharged  from  the  copper  solution  on  the  elec- 
trode connected  with  the  negative  pole  of  the  source  of  current, 
pass  into  the  molecular  state,  and  metallic  copper  separates 
upon  this  electrode,  while  the  anions  of  the  acid-residue  SO  4, 
migrate  to  the  electrode  connected  with  the  positive  pole, 
where  they  dissolve  copper,,  thus  giving  up  fresh  copper-ions- 
to  the  solution.  Hence  the  concentration  of  the  electrolyte 
remains  constant,  provided  electrolysis  lasts  not  too  long,  and 
the  current  introduced  is  not  stronger  than  just  necessary  for 
the  decomposition  of  the  cupric  sulphate  solution  ;  the  nature 
of  the  electrodes  themselves  remains  unchanged.  The  needle 
of  the  galvanometer  makes  one  deflection  and  when  the  cur- 
rent is  interrupted  returns  to  the  0  point,  thus  indicating  the 
absence  of  a  counter-current ;  the  electrodes  have  proved  them- 
selves as  non-polarizable. 

However,  the  case  is  different  when  an  electrolyte  is  electro- 
lyzed  between  insoluble  electrodes.  If  a  powerful  current  be 
conducted  through  a  platinum  anode  into  standard  snlphuric 
acid  (H2S04),  the  latter  is  decomposed  into  hydrogen-ions- 
which  go  to  the  platinum  cathode  while  the  S04-ions  migrate 
to  the  anode.  As  previously  mentioned,  the  S04-ions  cannot 
exist  in  a  free  state,  neither  can  they  dissolve  platinum  and, 
while  water  is  decomposed,  sulphuric  acid  and  oxygen-gas  are 
again  formed,  the  latter  being  separated  on  the  platinum 
anode.  The  hydrogen  separated  on  the  cathode  is  electro- 
positive towards  the  oxygen  separated  on  the  anode,  the  con- 
sequence being  that  from  the  hydrogen  of  the  cathode  a 
counter-current  flows  to  the  oxygen  of  the  anode,  which  is  in- 
dicated when  the  primary  current  is  interrupted  by  the  needle 
of  the  galvanometer,  instead  of  merely  returning  to  the  0 
point,  deflecting  in  a  direction  opposite  to  that  of  the  previous 
deflection,  and  returning  to  the  O  point  only  after  the  equal- 
ization of  the  charges  in  the  electrodes. 

The  counter-current  or   polarization-current   appears   also* 


MAGNETISM    AND    ELECTRICITY.  67 

when  two  different  metals  dip  in  one  electrolyte.  In  a  Volta 
cup  cell,  a  zinc  plate  and  a  copper  plate  connected  by  a  metal- 
lic wire  dip  in  dilute  sulphuric  acid.  A  current  flows  from 
the  copper  through  the  wire  to  the  zinc,  and  returns  from  the 
zinc  through  the  acid  to  the  copper,  decomposing  thereby  the 
acid  into  hydrogen  and  SO4.  The  hydrogen  separates  on  the 
copper,  the  acid-residue  S04  on  the  zinc,  and  dissolves  the 
latter,  zinc  sulphate  being  formed.  The  separated  hydrogen 
being  electro-positive  towards  the  separated  acid-residue,  a 
cur-rent  in  the  direction  from  the  copper  to  the  zinc  is  gener- 
ated, and  consequently  flows  in  a  direction  opposite  to  that  of 
the  main  current,  which  passes  from  the  zinc  to  the  copper. 
The  electro-motive  force  of  the  main  current  is  thus  decreased 
by  the  magnitude  corresponding  to  the  electro-motive  force  of 
this  counter-current. 

If  a  zinc  chloride  solution  be  electrolyzed  between  two  plat- 
inum electrodes,  zinc  separates  on  the  cathode  while  chlorine 
appears  on  the  anode.  If  the  current  be  interrupted,  a  galvano- 
scope  placed  on  the  electrodes  indicates  a  vigorous  counter- 
current  which  turns  from  the  zinc  deposit — hence  the  cathode 
— to  the  anode,  therefore  opposite  to  the  current  at  first  sup- 
plied. This  counter-current  originates  from  the  tendency  of 
the  substances  separated  on  the  electrodes  to  return,  in  conse- 
quence of  the  solution- tension,  to  the  ion  state,  and  this  ten- 
dency exists  during  the  entire  process  of  the  electrolysis. 

The  farther  the  metals  in  the  series  of  electro-motive  force 
are  distant  from  each  other,  the  greater  the  electro-motive 
force  which  the  polarization-current  possesses,  as  will  be  more 
particularly  shown  in  the  practical  part  of  this  work. 

Decomposition-pressure.  An  electric  current  can  only  pass 
through  an  electrolyte  and  decompose  it,  when  its  electro- 
motive force  possesses  a  certain  minimum  magnitude.  The 
characteristic  values  at  which  the  electrolytes  are  permanently 
decomposed  are  designated,  according  to  Le  Blanc,  as  their 
decomposition-values;  the  decomposition-pressure  being  the 
electro-motive  force  required  for  the  separation  of  the  electric 


68  ELECTRO-DEPOSITION    OF    METALS. 

charge  of  the  ions.  The  decomposition-values  of  solutions 
which  separate  metals  vary.  Le  Blanc  found  as  decomposi- 
tion-values of  solutions  which  contained  per  liter  one  combin- 
ing weight  of  the  metallic  salts,  for 

Zinc  sulphate,  2.35  volt ;  Cadmium  sulphate,  2.03  volt. 

Nickel  sulphate,  2.09  volt ;  Cadmium  chloride,  1.88  volt. 

Nickel  chloride,  1.85  volt;  Cobaltous  sulphate,  1.92  volt. 

Silver  nitrate,  0.70  volt;  Cobaltous  chloride,  1.78  volt. 

The  difference  in  the  decomposition  values  of  metallic  salt 
solutions  explains  the  feasibility  of  separating  from  a  solution 
which  contains  different  metals,  the  individual  metals,  one 
after  the  other,  free  from  other  admixtures. 

Velocity  of  ions.  It  has  previously  been  shown  that  no 
polarization-current  is  generated  when  a  cupric  sulphate  solu- 
tion is  for  a  short  time  elect roly zed  between  copper-electrodes. 
If,  however,  not  too  strong  a  current  be  for  a  longer  time 
passed  through  the  solution,  a  polarization-current  appears, 
the  origin  of  which  must  be  due  to  another  cause  than  the 
formation  of  a  gas  cell,  because  no  gases  are  separated  with 
not  too  strong  a  current.  It  has  been  shown  that  changes  of 
concentration  take  place  in  the  solution,  concentration  becom- 
ing greater  on  the  cathode  and  less  on  the  anode.  These 
changes  in  concentration  have  been  subjected  to  a  thorough 
investigation  by  Hittorf,  and  it  was  found  that  the  former 
view,  according  to  which  the  number  of  positive  and  negative 
ions  which  migrate  in  opposite  directions  through  an  elec- 
trolyte, must  be  equal,  was  an  erroneous  one.  The  mobility 
of  the  ions  varies,  and  depends  on  their  nature.  If,  for  in- 
stance, hydrochloric  acid  be  electrolyzed,  the  hydrogen-ion 
migrates  about  five  times  as  rapidly  to  the  cathode  as  the 
chlorine-ion  to  the  anode.  The  cations  and  anions  of  the 
metallic  salts  act  in  a  similar  manner,  and  consequently  a 
greater  concentration  will  take  place  on  the  cathode  and  a  re- 
duction in  the  content  of  metal  on  the  anode,  when  the  anions 
migrate  more  slowly  than  the  cations ;  and  vice  versa,  concen- 
tration will  increase  on  the  anode  when  the  anions  migrate 
more  rapidly  than  the  cations. 


MAGNETISM    AND    ELECTRICITY.  69 

The  middle  layer  of  the  electrolyte  always  remains  un- 
changed and  of  the  same  concentration,  the  changes  in  con- 
centration being  shown  in  the  layers  of  fluid  surrounding  the 
electrodes,  and  these  differences  in  concentration  also  effect 
the  formation  of  a  current,  which,*  according  to  the  nature  of 
the  electrodes  may  flow  in  the  sense  of  the  main  current  or  in 
that  of  the  counter-current. 

The  quotients  obtained  by  dividing  the  distances,  which  the 
cations  and  anions  perform  in  the  same  time,  by  the  total  dis- 
tance of  the  road  traveled  by  the  two  ions,  Hittorf  designates 
as  the  transport-values  of  the  respective  ions. 

We  herewith  conclude  the  theoretical  considerations,  and 
will  later  on  have  occasion  to  touch  upon  other  fundamental 
electrolytical  principles  of  less  importance. 


III. 

SOURCES  OF  CURRENT. 


CHAPTER  III. 

VOLTAIC    CELLS,    THERMO- PILES,    DYNAMO-ELECTRIC    MACHINES, 

ACCUMULATORS. 

THE  sources  of  current  which  are  used  for  the  electro- 
deposition  of  metals  are :  Voltaic  cells,  thermo-piles,  dynamo- 
electric  machines,  and  accumulators. 

A.  VOLTAIC  CELLS. 

It  is  not  within  the  province  of  this  work  to  enter  into  a 
detailed  description  of  all  the  forms  of  voltaic  cells,  because 
the  number  of  such  constructions  is  very  large,  and  the  num- 
ber of  those  which  have  been  successfully  and  permanently 
introduced  for  practical  work  is  comparatively  small. 

In  the  theoretical  part,  we  have  learned  the  origin  of  the 
current  and  the  explanation  of  its  origin  by  the  solution- 
tension  of  the  metals  or  the  osmotic  pressure  of  the  solutions, 
and  we  know  further  that  in  a  voltaic  cell  chemical  energy  is 
converted  into  electrical  energy.  In  speaking  of  polarization 
which  is  formed  when  two  different  metals  dip  in  one  fluid, 
we  have  seen  that  the  hydrogen  liberated  on  the  copper  in 
a  Volta  cup  cell  generates  a  counter-current  which  weakens 
the  principal  current.  This  hydrogen  appearing  on  the  posi- 
tive pole  is  the  cause  of  a  rapid  decrease  in  the  efficiency  of 
the  cell,  and  all  cells  in  which  the  hydrogen  on  the  cathode 
is  not  neutralized  by  suitable  means,  are  called  inconstant  cells, 
while  cells  in  which  the  hydrogen  is  removed  in  a  physical 

(70) 


SOURCES    OF    CURRENT.  71 

way  or  by  chemical  agents  which  oxidize  it,  are  called  constant 
•cells. 

The  original  form  of  voltaic  cells,  the  voltaic  pile,  consisting 
of  zinc  and  copper  plates  separated  from  one  another  by  moist 
pieces  of  cloth,  has  already  been  mentioned  on  p.  2,  as  well  as 
its  disadvantages,  which  led  to  the  construction  of  the  so-called 
•trough  battery.  The  separate  elements  of  this  battery  are 
square  plates  of  copper  and  zinc,  soldered  together,  and 
parallel  fixed  into  water-tight  grooves  in  the  sides  of  a  wooden 
trough  so  as  to  constitute  water-tight  partitions,  which  are 
filled  with  acidulated  water.  The  layer  of  water  serves  here 
as  a  substitute  for  the  moist  pieces  of  cloth  in  the  voltaic  pile. 

In  other  constructions  the  fluid  is  in  different  vessels,  each 
vessel  containing  a  zinc  and  a  copper  plate  which  do  not 
touch  one  another,  the  copper  plate  of  the  one  vessel  being 
connected  with  the  zinc  plate  of  the  next,  and  so  on. 

In  all  cells  with  one  exciting  fluid,  the  current  is  quite 
strong  at  first,  but  decreases  rapidly  for  the  reasons  given  above. 
On  the  one  hand,  during  the  interruption  of  the  current  a 
.change  takes  place  in  the  fluid  by  the  local  etfect  in  the  cell, 
and,  on  the  other,  the  zinc  forms  with  the  impurities  contained 
in  it,  small  voltaic  piles  with  a  closed  circuit,  in  consequence 
of  which  the  cell  performs  a  certain  chemical  work  even  when 
the  current  is  interrupted.  The  local  action  can  be  reduced 
to  a  minimum  by  amalgamating  the  zinc.  Such  amalgama- 
tion is  also  a  protection  against  the  above-mentioned  chemical 
work  of  the  cell,  the  hydrogen  bubbles  adhering  so  firmly 
during  the  interruption  of  the  current  to  the  amalgamated 
homogeneous  surface  as  to  form  a  layer  of  gas  around  the  zinc 
surface  by  which  its  contact  with  the  fluid  is  prevented. 

Amalgamation  may  be  effected  in  various  ways.  The  zinc  is 
•either  scoured  with  coarse  sand  moistened  with  dilute  sulphuric 
or  hydrochloric  acid,  or  pickled  in  a  vessel  containing  either  of 
the  dilute  acids.  The  mercury  may  be  either  mixed  with  moist 
sand  and  a  few  drops  of  dilute  sulphuric  acid,  and  the  zinc  be 
amalgamated  by  applying  the  mixture  by  means  of  a  wisp  of 


72  ELECTRO-DEPOSITION    OF    METALS. 

straw  or  a  piece  of  cloth  ;  or  the  mercury  may  be  applied  by 
itself  by  means  of  a  steel-wire  brush,  the  brush  being  dipped  in 
the  mercury  and  what  adheres  is  quickly  distributed  upon  the 
zinc  by  brushing  until  the  entire  surface  acquires  a  mirror-like- 
appearance.  The  most  convenient  mode  of  amalgamation  is 
to  dip  the  zinc  in  a  suitable  solution  of  mercury  salt  and  rub 
with  a  woolen  rag.  A  suitable  solution  is  prepared  by  dissolv- 
ing 10  parts  by  weight  of  mercurous  nitrate  in  100  parts  of 
warm  water,  to  which  pure  nitric  acid  is  added  until  the  milky 
turbidity  disappears.  Another  solution,  which  is  also  highly 
recommended,  is  obtained  by  dissolving  10  parts  by  weight  of 
mercuric  chloride  (corrosive  sublimate)  in  12  parts  of  hydro- 
chloric acid  and  100  of  water,  or  by  dissolving  10  parts  by 
weight  of  potassium  mercuric  cyanide  and  2  parts  potassium 
cyanide  in  100  parts  of  water.  In  order  to  preserve  as  much 
as  possible  the  coating  of  mercury  upon  the  zinc,  sulphuric 
acid  saturated  with  neutral  mercuric  sulphate  is  used  for  the 
cells.  For  this  purpose  frequently  shake  the  concentrated 
sulphuric  acid  (before  diluting  with  water)  with  the  mercury 
salt.  As  much  mercuric  sulphate  or  mercuric  chloride  as  will 
lie  upon  the  point  of  a  knife  may  also  be  added  in  the  cells  to 
the  zinc. 

Instead  of  the  addition  of  mercuric  sulphate,  Bouant  recom- 
mends to  compound  the  dilute  sulphuric  acid  with  2  per  cent, 
of  a  solution  obtained  as  follows :  Boil  a  solution  of  3J  ozs.  of 
nitrate  of  mercury  in  1  quart  of  water,  together  with  an  excess 
of  a  mixture  of  equal  parts  of  mercuric  sulphate  and  mercuric 
chloride,  and,  after  cooling,  filter  and  use  the  clear  solution. 

Smee  cell.  This  cell  consists  of  a  zinc  plate  and  a  platinized 
silver  plate  dipping  into  dilute  acid.  It  may  be  formed  of  two 
zinc  plates  mounted  with  the  platinized  silver  between  them 
in  a  wooden  frame,  which  being  a  very  feeble  conductor  ma}' 
carry  away  a  minute  fraction  of  the  current,  but  serves  to  hold 
the  metals  in  position,  so  that  quite  a  thin  sheet  of  silver  may 
be  employed  without  fear  of  its  bending  out  of  shape  and 
making  a  short  circuit.  Platinizing  is  effected  by  suspending 


SOURCES    OF    CURRENT. 


the  silver  plates  in  a  vessel  filled  with  acidulated  water,  add- 
ing some  chloride  of  platinum  and  placing  the  vessel  in  a 
porous  clay  cell  filled  with  acidulated  water  and  containing  a 
piece  of  zinc,  the  latter  being  connected  with  the  silver  plates 
by  copper  wire.  The  platinum  coating  obtained  in  this  man- 
ner is  a  black  powder  which  roughens  the  surfaces,  in  conse- 
quence of  which  the  bubbles  of  hydrogen  become  readily  de~ 
tached,  and  polarization  is  less  than  with  silver  plates  not 
platinized.  The  use  of  electrolytically-prepared  copper  plates, 
which  are  first  strongly  silvered  and  then  platinized,  is  still 
more,  advantageous  on  account  of  their  greater  roughness. 
To  increase  the  constancy  of  the  cell,  it  is  advisable  to  add: 
some  chloride  of  platinum  to  the  dilute  acid  of  the  element. 

The  Smee  cell  is  still  frequently  used  in  England  and  the 
United  States  with  silver  and  gold  plating  solutions.  Its 
electro-motive  force  is  about  0.48  volt. 

As  previously  mentioned,  polarization  can  be  entirely 
avoided  only  by  allowing  the  electro-negative  pole-plate  to- 
dip  in  a  fluid  which,  by  combustion,  reduces  the  hydrogen 
evolved  to  water,  or,  in  other  words,  which  immediately  oxi- 
dizes the  hydrogen  to  water.  From  this 
conviction  originated  the  so-called  constant 
cells  with  two  fluids,  the  first  of  these  cells 
being,  in  1829,  constructed  by  Becquerel, 
which,  in  1836,  was  succeeded  by  the  more 
effective  one  of  Daniell. 

Daniell  cell.  In  its  most  usual  form 
Darnell's  cell  (Fig.  8)  consists  of  a  glass 
vessel,  a  copper  cylinder,  a  porous  earthen- 
ware pot  and  a  zinc  rod  suspended  in  the 
latter.  The  glass  vessel  is  filled  with 
saturated  blue  vitriol  solution,  a  small  piece  of  blue  vitriol 
being  added,  and  the  porous  earthenware  pot  with  dilute 
sulphuric  acid  about  1  part  of  acid  to  12  to  20  parts  of  water. 
The  acid  residue  S04  migrates  to  the  positive  zinc,  and  there 
forms  zinc  sulphate,  while  the  hydrogen  which  is  liberated  on 


FIG. 


74 


ELECTRO-DEPOSITION    OF    METALS. 


Meidinger  cell. 


FIG.  9. 


the  electro-negative  copper,  reduces  from  the  blue  vitriol 
solution  an  equivalent  quantity  of  copper,  which  is  deposited 
upon  the  electro-negative  plate  according  to  the  following 
equation : 

CuS04     +     2H  '  =     Cu     +     H2S04 

Cupric  sulphate.       Hydrogen.       Copper.       Sulphuric  acid. 

Thus  the  hydrogen  is  removed  by  its  combining  with  the 
acid-residue  S04  to  sulphuric  acid.  A  drawback  of  the 
Daniell  cell  is  that  the  blue  vitriol  solution  diffuses  into  the 
porous  pot,  where  it  is  decomposed  by  the  zinc  on  coming  in 
contact  with  it,  and  the  copper  is  separated  upon  the  zinc,  the 
efficiency  being  thus  destroyed,  or  at  least  very  much  weak- 
ened. The  electro-motive  force  of  the  Daniell  cell  is  quite 
exactly  1.1  volt. 

This  may  be  considered  a  modified  Daniell 
cell.  Like  the  Callaud  cell,  it  has  no 
porous  partition,  the  fixture  of  the  two 
fluids  being  retarded  by  their  different 
specific  gravities.  The  form  of  the  Meid- 
inger cell,  as  most  generally  used,  is 
shown  in  Fig.  9. 

Upon  the  bottom  of  a  glass  vessel,  A, 
provided  at  b  with  a  shoulder,  stands  a 
small  glass  cylinder,  K,  which  contains 
the  electro-negative  copper  cylinder  D; 
from  the  latter  a  conducting  wire  leads  to 
the  exterior.  Upon  the  shoulder,  at  6, 
rests  the  zinc  cylinder  Z,  which  is  also 
provided  with  a  conducting  wire  leading 
to  the  exterior.  The  balloon  C  closes  the 
vessel  by  being  placed  upon  it.  The  balloon  is  filled  with  pieces 
of  blue  vitriol  and  Epsom  salt  solution.  The  entire  cell  is  also 
filled  with  Epsom  salt  solution  (1  part  Epsom  salt  to  5  water.) 
In  the  balloon  C  concentrated  solution  of  blue  vitriol  is  formed 
which  flows  into  the  glass  cylinder  K.  If  the  battery  is  not 


SOURCES    OF    CURRENT.  75 

-closed,  the  concentrated  copper  solution  remains  quietly  stand- 
ing in  K,  its  greater  specific  gravity  preventing  it  from  rising 
higher  and  reaching  the  zinc.  If,  however,  the  current  be 
closed,  zinc  is  dissolved,  while  metallic  copper  is  separated 
from  the  blue  vitriol  solution,  and  concentrated  solution  flows 
from  the  balloon  0  to  the  same  extent  as  the  blue  vitriol  solu- 
tion in  D  becomes  dilute  by  the  separation  of  copper.  Hence 
the  action  of  the  cell  remains  constant  for  quite  a  long  time, 
and  of  all  the  modified  forms  of  Darnell's  cell  consumes  the 
least  blue  vitriol  for  a  determined  quantity  of  current.  How- 
ever, in  consequence  of  its  great  internal  resistance  (3  to  5 
ohms,  according  to  its  size)  its  current-strength  is  small.  The 
-electro-motive  force  of  the  Meidinger  cell  is  0.95  volt. 

Bunsen  cell.  Bunsen,  in  1841,  replaced  the  expensive  plati- 
num by  prisms  cut  from  gas-carbon,  which  is  still  less  electro- 
negative than  platinum,  and  very  hard  and  solid,  so  that  it 
perfectly  resists  the  action  of  the  nitric  acid.  In  place  of  the 
gas-carbon  an  artificial  carbon  may  be  prepared  by  kneading 
a  mixture  of  pulverized  coal  and  coke  with  sugar  solution  or 
syrup,  bringing  the  mass  under  pressure  into  suitable  iron 
moulds  and  heating  it  red-hot,  the  air  being  excluded.  After  t 
cooling  the  carbon  is  again  saturated  with  sugar  solution 
(others  use  tar,  or  a  mixture  .of  tar  and  glycerine)  and  again 
heated,  the  air  being  excluded.  These  operations  are,  if 
necessary,  repeated  once  more,  especially  when  great  demands 
are  made  on  the  electro-motive  force  and  solidity  of  the 
artificial  carbons. 

In  the  Bunsen  cell  the  zinc  electrode  dips  in  dilute  sulphuric 
acid  and  the  carbon  in  concentrated  nitric  acid.  Independent 
of  the  fact  that  by  reason  of  its  rough  surface,  the  carbon  has 
by  itself  the  tendency  to  repel  the  hydrogen-bubbles  and  thus 
acts  to  a  certain  degree  as  a  depolarizer,  depolarization,  i.  e.t 
the  removal  of  the  hydrogen-bubbles  which  produce  polariza- 
tion, is  most  effectively  assisted  by  the  nitric  acid,  the  hy- 
drogen being  oxidized  to  water  according  to  the  following 
equation,  while  the  nitric  acid  is  reduced  to  nitric  oxide : 


76  ELECTRO-DEPOSITION    OF    METALS. 

2HNO,         +         6H         =         2NO       +       4H20 

o 

Nitric  acid.  Hydrogen.  Nitric  oxide.  Water. 

The  processes  which  take  place  in  the  Bunsen  cell  are  as 
follows :  From  the  positive  carbon  a  current  passes  through 
the  wire  to  the  zinc  and  returns  from  the  latter  through  the 
dilute  sulphuric  acid  to  the  carbon.  The  sulphuric  acid 
(H2S04),  is  thereby  decomposed  to  hydrogen  and  sulphuric 
acid  residue  S04  the  hydrogen  migrating  to  the  carbon  and  is 
oxidized  to  water  by  the  nitric  acid,  while  the  sulphuric  acid 
residue  migrates  .to  the  zinc  and  combines  with  it  to  zinc  sul- 
phate (ZnS04)  as  illustrated  by  the  following  scheme : 

Zinc      I      Sulphuric  acid    |    Nitric  acid  Carbon 

(-)  Zn  I          ~~H£04  |        2HN03  (  +  )  C 

\  \ 

\  \/ 


ZnSO4<(  Zinc  sulphate)  2HNO3  (Nitric  acid)  H2  (Hydrogen) 


N2O4  +2H20 

Nitrogen  tetroxide  Water. 

To  prevent  the  two  fluids  from  mixing,  the  use  of  a  porous 
partition  is  required,  the  same  as  in  Darnell's  cell. 

Figs.  10,  11  and  12  show  three  forms  of  Bunsen's  cell  gen- 
erally used. 

Fig.  11  is  the  most  convenient  and  practical  form.  It  con- 
sists of  an  outer  vessel  of  glass  or  earthenware.  In  this  is 
placed  a  cylinder  of  zinc  in  which  stands  a  porous  clay  cup, 
and  in  the  latter  the  prism  of  gas-carbon.  This  substance  is 
the  graphite  of  the  gas  retorts.  It  is  not  coke.  It  is  easily 
procurable  in  lump  at  a  small  price,  but  costs  much  more  when 
cut  into  plates,  as,  when  the  material  is  good,  it  is  exceedingly 


SOURCES    OF    CURRENT. 


77 


difficult  to  work.  It  is  generally  cut  with  a  thin  strip  of  iron 
and  watered  silver-sand.  Blocks  for  Bunsen  cells  cost  less  be- 
cause they  are  more  easily  produced.  Rods  for  Bunsen  cells 
should  be  a  few  inches  longer  than  the  pots  to  protect  the  top 
from  contact  with  the  acid.  A  good  carbon  is  of  a  clear  gray 
appearance,  has  a  finely  granulated  surface,  and  is  very  hard. 
A  band  of  copper  is  soldered  or  secured  by  means  of  a  bind- 
ing-screw to  the  zinc  cylinder,  while  the  prism  of  gas  carbon 
carries  the  binding-screw  (armature),  as  seen  in  Fig.  10  in  the 
upper  part  of  which  a  copper  sheet  or  wire  is  fixed  for  the 
transmission  of  the  current.  The  other  vessel  is  filled  with 


FIG.  10. 


FIG.  11. 


FIG.  12. 


dilute  sulphuric  acid  (1  part  by  weight  of  sulphuric  acid  of 
66°  Be. — free  from  arsenic — and  15  parts  by  weight  of  water), 
and  the  porous  cup  with  concentrated  nitric  acid  of  at  least 
36°  Be.,  or  still  better  40°  Be.,  care  being  had  that  both 
fluids  have  the  same  level. 

In  Fig.  11  the  cylinder  of  artificial  carbon  is  in  the  glass 
vessel,  while  the  zinc,  which,  in  order  to  increase  its  surface, 
has  a  star-shaped  cross-section,  is  placed  in  the  porous  clay 
cup.  In  this  case  the  outer  vessel  is  filled  with  concentrated 
nitric  acid,  and  the  clay  cell  with  dilute-sulphuric  acid. 

The  form  of  the  Bunsen  cell  shown  in  Fig.  10  is  more 
advantageous,  because  its  effective  zinc  surface  can  be  kept 
larger. 


78  ELECTRO-DEPOSITION    OF   METALS. 

Fig.  12  shows  a  plate  cell  such  as  is  chiefly  used  for  plunge 
batteries. 

Fig.  13  shows  an  improved  Buusen  cell  of  great  power.  It 
is  particularly  adapted  for  use  with  nickel,  copper,  brass  or 
bronze  solutions.  It  has  an  electro- motive  force  of  1.9  volts. 
Where  the  absence  of  power  prevents  the  use  of  a  dynamo,  a 
battery  of  these  cells  is  very  suitable  for  nickel  plating. 

The  Bunsen  cells  are  much  used  for  electro-deposition,  since 
they  possess  a  high  electro-motive  force  (1.88  volts),  and,  on 
account  of  slight  resistance  (0.5  to  0.25  ohm,  according  to 

FIG.  13. 


their  size),  develop  considerable  current-strength.  Like  the 
Grove  cells,  they  have  the  inconvenience  of  evolving  vapors  of 
nitrogen  tetroxide,  which  are  not  only  injurious  to  health,  but 
also  attack  the  metallic  articles  in  the  workshop.  Wherever 
possible  they  should  be  placed  in  a  box  at  such  a  height  that 
they  may  be  readily  manipulated.  The  box  should  have 
means  of  ventilation  in  such  a  way  that  the  air  coming  in  at 
the  lower  part  will  escape  at  the  top  through  a  flue,  and  carry 
away  with  it  the  acid  fumes  disengaged.  It  is  still  better  to 
keep  the  cells  in  a  room  separate  from  that  where  the  baths 
and  metals  are  located.  Furthermore,  as  the  nitric  acid  be- 


SOURCES    OF    CURRENT.  79' 

comes  diluted  by  the  oxidation  of  the  hydrogen,  and  the  sul- 
phuric acid  is  consumed  in  the  formation  of  sulphate  of  zinc, 
the  acids  have  to  be  frequently  renewed. 

To  get  rid  of  the  acid  vapors,  as  well  as  to  render  the  cells 
more  constant,  A.  Duprei  has  proposed  the  use  of  a  30  per 
cent,  solution  of  bisulphate  of  potash  in  water,  in  place  of  the 
dilute  sulphuric  acid,  and  a  mixture  of  water  600  parts,  con- 
centrated sulphuric  acid  400,  sodium  nitrate  500,  and  bichro- 
mate of  potash  60,  in  place  of  the  nitric  acid. 

The  following  method  can  be  recommended :  The  outer 
vessel  which  contains  the  zinc  cylinder  is  filled  with  a  mode- 
rately concentrated  (about  30  per  cent.)  solution  of  bisulphate 
of  potash  or  soda,  and  the  clay  cup  with  solution  of  chromic 
acid — 1  part  chromic  acid  to  5  parts  water.  As  soon  as  the 
electro-motive  force  of  the  cell  abates,  it  is  strengthened  by 
the  addition  of  a  few  spoonfuls  of  pulverized  chromic  acid  to 
the  chromic  acid  solution.  It  is  preferable  to  use  the  chromic 
acid  in  the  form  of  a  powder  especially  prepared  for  this  pur- 
pose than  a  chromic  acid  solution  produced  by  mixing  potas- 
sium dichromate  solution  with  sulphuric  acid,  such  a  solution 
having  a  great  tendency  to  form  crystals  which  exerts  a  dis- 
turbing effect.  Solution  of  sodium  dichromate  compounded, 
with  sulphuric  acid  does  not  show  this  drawback. 

The  efficiency  of  the  chromic  acid  solution  rapidly  abates  in 
a  comparatively  short  time,  the  electro-motive  force  of  the  cell 
decreasing  in  a  few  hours  and  chromic  acid  has  frequently  to 
be  added,  or  the  cell  eventually  refilled. 

Dr.  Langbein  has  succeeded  in  preparing  a  soluble  chrom- 
ium combination  which  depolarizes  rapidly  and  for  a  longer 
time  maintains  the  efficiency  of  the  cell  constant.  With  a 
single  filling  of  this  solution,  the  battery  has  been  kept  work- 
ing for  six  days,  from  morning  to  evening,  without  refilling 
being  required.  During  the  night  the  battery  remained 
filled,  but  inactive.  The  solution  is  obtained  by  treating 
Langbein's  chromic  iron  powder  with  concentrated  sulphuric 
acid  and  carefully  diluting  with  water. 


80  ELECTRO-DEPOSITION    OF    METALS. 

The  electro-motive  force  of  a  cell  filled  with  this  solution  is 
1.8  volts.  Considering  the  lasting  quality  and  great  con- 
stancy, and  consequent  cheapness,  as  well  as  freedom  from 
odor  of  this  solution,  it  would  appear  to  be  the  most  suitable. 

If  nitric  acid  is  us'ed  for  filling  the  cells  it  is  advisable  in 
order  to  decrease  the  vapors,  to  cover  the  acid  with  a  layer  of 
oil  J  to  |  inch  deep. 

The  binding-screws  which  effect  the  metallic  contacts  must 
of  course  be  frequently  inspected  and  cleaned,  the  latter  being 
•best  done  by  means  of  a  file  or  emery  paper.  It  is  advisable 
to  place  a  piece  of  platinum  sheet  between  the  binding  surface 
of  the  carbon  armature  and  the  carbon,  in  order  to  prevent 
the  acid,  rising  through  the  capillarity  of  the  carbon,  from 
acting  directly  upon  the  armature  (generally  brass  or  copper). 
To  prevent  the  acid  from  rising,  the  upper  portions  of  the 
carbons  may  be  impregnated  with  paraffine.  For  this  pur- 
pose {he  carbons  are  placed  f  to  1  inch  deep  in  melted  paraffine 
and  allowed  to  remain  10  minutes.  On  the  sides  where  the 
armature  comes  in  contact  with  the  carbon,  an  excess  of  par- 
-affine  is  removed  by  scraping  with  a  knife-blade  or  rasp. 

Treatment  of  Bunsen  cells.  Before  use  the  zincs  should  be 
-carefully  amalgamated  according  to  one  of  the  methods  given 
on  page  71.  The  nitric  acid  need  not  be  pure,  the  crude  com- 
mercial article  answering  very  well,  but  it  should  be  as  concen- 
trated as  possible  and  show  at  least  30°  Be.  Carbons  of  hard 
retort-carbon  are  to  be  preferred,  although  those  cut  from 
carbon  produced  in  gas-houses,  gasifying  coal  without  an 
addition  of  lignite,  may  also  be  used.  Artificial  carbon,  if 
employed,  should  be  examined  as  to  its  suitability,  tlie  non- 
success  of  the  plating  process  being  frequently  attributed  to  the 
composition  of  the  bath,  when  in  fact  it  is  due  to  the  defective 
carbons  of  the  cells.  In  order  to  avoid  an  unnecessary  con- 
sumption of  zinc  and  acid,  the  cells  are  taken  apart  when  not 
in  use,  for  instance,  over  night.  Detach  the  brass  armature 
of  the  carbon  and  lay  it  in  water  to  which  some  chalk  has 
been  added.  Lift  the  carbon  from  the  clay  cylinder  and  place 


SOUKCES    OF    CURRENT.  81 

it  in  a  porcelain  dish  or  earthenware  pot ;  empty  the  nitric  acid 
of  the  clay  cup  into  a  bottle  provided  with  a  glass  stopper ; 
place  the  clay  cup  in  a  vessel  of  water,  and  finally  take  the 
zinc  from  the  dilute  sulphuric  acid  and  place  it  upon  two 
sticks  of  wood  laid  across  the  glass  vessel  to  drain  off.  In  put- 
ting the  cells  together  the  reverse  order  is  followed,  the  zinc 
being  first  placed  in  the  glass  vessel  and  then  the  carbon  in  the 
porous  clay  cup.  The  latter  is  then  filled  about  three-quarters 
full  with  used  nitric  acid,  and  fresh  acid  is  added  until  the  fluid 
in  the  clay  cup  stands  at  a  level  with  that  in  the  outer  vessel. 
The  cleansed  brass  armature  is  then  screwed  upon  the  carbon. 
Finally,  add  to  the  dilute  sulphuric  acid  in  the  outer  vessel  a 
small  quantity  of  concentrated  sulphuric  acid  saturated  with 
mercury  salt. 

It  is  advisable  to  have  at  least  a  duplicate  set  of  porous  clay 
•cups,  and,  in  putting  the  cells  together,  to  use  only  cups  which 
have  been  thoroughly  soaked  in  water.  The  reason  for  this 
is  as  follows:  The  nitric  acid  fills  the  pores  of  the  cup,  and, 
finally  reaching  the  zinc  of  the  outer  vessel,  causes  strong  local 
action  and  a  correspondingly  rapid  destruction  of  the  zinc.  It 
is,  therefore,  best  to  change  the  clay  cups  every  day,  allowing 
those  which  have  been  in  use  to -lie  in  water  the  next  day  with 
frequent  renewal  of  the  water.  For  the  same  reason  the  nitric 
acid  in  the  clay  cup  should  not  be  at  a  higher  level  than  the 
sulphuric  acid  in  the  outer  vessel. 

When  the  Bunsen  cells  are  in  steady  use  from  morning  till 
night,  the  acids  will  have  to  be  entirely  renewed  every  third 
or  fourth  day.  The  solution  of  sulphate  of  zinc  in  the  outer 
vessel,  being  of  no  value,  is  thrown  away,  while  the  acid  of  the 
•clay  cells  may  be  mixed  with  an  equal  volume  of  concentrated 
sulphuric  acid,  and  this  mixture  can  be  used  as  a  preliminary 
pickle  for  brass  and  other  copper  alloys. 

The  Leclanche  cell  (zinc  and  carbon  in  sal-ammoniac  solu- 
tion with  manganese  peroxide  as  a  depolarizer)  need  not  be 
further  described,  it  not  being  adapted  for  regular  use  in  electro- 
plating. It  is  in  very  general  use  for  electric  bells,  its  great 
6 


82 


ELECTRO-DEPOSITION    OF    METALS. 


recommendation  being  that,  when  once  charged,  it  retains  its 
power  without  attention  for  a  long  time. 

Cupric  oxide  cell.  Lallande  and  Chaperon  have  introduced 
a  cupric  oxide  cell  shown  in  Fig.  14  which  possesses  certain 
advantages.  It  consists  of  the  outer  vessel  G,  of  cast-iron  or 
copper,  which  forms  the  negative  pole-surface,  and  to  which 
the  wire  leading  to  the  anodes  is  attached,  and  a  strip  of  zinc, 
Z,  coiled  in  the  form  of  a  spiral,  which  is  suspended  from  an. 

FIG.  14. 


ebonite  cover  carrying  a  terminal  connected  with  the  zinc. 
The  hermetical  closing  of  the  vessel  G  by  the  ebonite  cover  is 
effected  by  means  of  three  screws  and  an  intermediate  rubber 
plate.  Upon  the  bottom  of  the  vessel  G  is  placed  a  3  to  4  inch 
deep  layer  of  cupric  oxide,  0,  and  the  vessel  is  filled  with  a 
solution  of  50  parts  of  caustic  potash  in  100  of  water.  When 
the  cell  is  closed,  decomposition  of  water  takes  place,  the  oxy- 
gen which  appears  on  the  zinc  forming  with  the  latter  zinc 
oxide,  which  readily  dissolves  in  the  caustic  potash  solution, 
while  the  hydrogen  is  oxidized,  and  cupric  oxide  at  the  same 
time  reduced  to  copper.  When  the  cell  is  open,  i.  e.,  the 
circuit  not  closed,  neither  the  zinc  nor  the  cupric  oxide  is. 


SOURCES    OF    CURRENT.  83 

attacked,  and  hence  no  local  action  nor  any  consumption  of 
material  takes  place.  The  electro-motive  force  of  this  cell  is 
0.98  volt,  and  its  internal  resistance  very  low.  It  is  remark- 
ably constant,  and  is  well  adapted  for  electro-plating  purposes 
by  using  two  of  them  for  one  Bunsen  cell.  The  following 
rules  have  to  be  observed  in  its  use  :  It  is  absolutely  necessary  ' 
that  the  ebonite  cover  should  hermetically  close  the  vessel  G, 
as  otherwise  the  caustic  potash  solution  would  absorb  carbonic 
acid  from  the  air,  whereby  carbonate  of  potash  would  be 
formed,  which  would  weaken  the  exciting  action  of  the  solu- 
tion. Further,  the  vessels  G  which  form  one  of  the  poles  must 
be  insulated  one  from  the  other  as  well  as  from  the  ground,  as 
otherwise  a  loss  of  current  or  defective  working  would  be  the 
consequence. 

The  regeneration  of  the  cuprous  oxide  or  metallic  copper 
formed  by  reduction  from  the  cupric  oxide  to  cuprous  oxide, 
requires  it  to  be  subjected  to  calcination  in  a  special  furnace. 
The  expense  connected  with  this  operation  is,  however,  about 
the  same  as  that  of  procuring  a  fresh  supply  of  cupric  oxide. 
Lallande  himself,  as  well  as  Edison,  endeavored  to  bring  the 
pulverulent  cupric  oxide  into  compact  plates,  but  the  regener- 
ation of  these  plates  was  still  more  troublesome.  By  treat- 
ment with  various  chemical  agents,  Dr.  Bottcher,  of  Leipsic, 
has  succeeded  in  producing  porous  plates  of  cupric  oxide 
which,  after  subsequent  reduction  by  absorption  of  oxygen 
from  the  air,  can  be  readily  re-oxidized  to  cupric  oxide,  but  as 
far  as  we  know  of,  cells  with  these  plates  have  not  been  intro- 
duced into  commerce. 

Cupron  cell.  The  cell  brought  into  commerce  under  this 
name  by  Umbreit  &  Matthes  is  a  modification  of  the  Lallande 
and  Chaperon  cell,  it  being  furnished  with  a  cuprous  oxide 
plate.  A  square  glass  vessel  or  vat,  furnished  with  a  hard 
rubber  cover,  contains  two  zinc  plates  and  between  them  the 
porous  cuprous  oxide  plate.  The  glass  vessel  is  filled  with  20 
per  cent,  caustic  soda  solution,  and  the  current  is  delivered  by 
means  of  two  binding  screws  on  the  outside  of  the  cover.  The 


84  ELECTRO-DEPOSITION    OF    METALS. 

zinc  dissolves,  zinc-oxide-soda  being  formed  according  to  the 
following  scheme,  while  the  cuprous  oxide  is  reduced  to  copper: 

Cuprous  oxide 

CuO(  +  ) 


Zinc  oxide  soda. 


The  reduced  positive  pole  plates  are  regenerated  by  rinsing 
in  water  and  keeping  them  in  a  warm  place  for  20  to  24  hours, 
it  being  only  necessary  to  replace  the  caustic  soda  solution 
which  has  become  saturated  with  zinc  oxide.  The  electro- 
motive force  of  the  cell  is  0.8  volt;  the  standard  current- 
strength,  according  to  the  size  of  the  cells,  1,  2,  4,  and  8  am- 
peres. Like  the  Lallande  and  Chaperon  cell,  this  cell  works 
without  giving  off  any  odor  and  the  remarks  regarding  her- 
metical  closing  of  the  former  also  apply  to  the  latter.  An 
addition  of  sodium  hyposulphite  to  the  caustic  soda  solution  is 
recommended  as  being  productive  of  uniform  wear  and  greater 
durability  of  the  zinc  plates. 

According  to  Jordis'  investigations  the  use  of  potash  lye 
with  15  per  cent,  potassium  hydrate  is  more  advantageous,  as 
well  to  heat  the  plates  for  the  purpose  of  regeneration  to 
302°  F. 

The  elements  of  Marie,  Davy,  Naudet,  Duchemin,  Sturgeon, 
Trouville,  and  others,  being  of  little  practical  value  may  be 
passed  over. 

Plunge  batteries.  For  constructive  reasons  only  one  fluid  is 
used  into  which  the  zinc  plates  as  well  as  the  carbon  plates 
dip,  a  solution  of  chromic  acid  prepared  by  dissolving  10  parts 
of  potassium  dichromate,  or  better  sodium  dichromate,  and  -5^ 
part  of  mercuric  sulphate  in  100  parts  of  water,  and  adding  38 
parts  of  pure  concentrated  sulphuric  acid,  being  employed. 


SOURCES    OF    CURRENT. 


85 


A  plunge  battery,  as  constructed  by  Fein,  consists  of  a 
wooden  box,  which  contains  in  two  rows  six  vessels  into  which 
dip  the  zinc  and  carbon  plates.  The  latter  are  secured  to 
wooden  cross-pieces  furnished  with  handles,  and  may  be 
maintained  at  any  height  desired  by  the  notches  in  the  stand- 
ards. According  to  the  current-strength  required  the  plates 
are  allowed  to  dip  in  more  or  less  deeply. 

In  using  the  above-mentioned  chromic  acid  solution  brigin- 

FIG.  15. 


ally  recommended  by  Bunsen,  the  cells  first  develop  a  very 
strong  current,  which,  however,  in  a  comparatively  short  time 
becomes  weaker  and  weaker.  The  current-strength  can  be  in- 
creased by  adding  at  intervals  a  few  spoonfuls  of  pulverized 
chromic  acid  to  the  chromic  acid  solution,  which,  however, 
finally  remains  without  effect,  when  the  battery  has  to  be 
freshly  filled.  Hence  these  batteries  are  not  suitable  for 


86 


ELECTRO-DEPOSITION    OF    METALS. 


FIG.  16. 


electro-plating  operations  requiring  a  constant  current  for  some 
time,  but  they  may  be  employed  for  temporary  use. 

If  plunge  batteries  are  to  be  used  for  constant  work  in  elec- 
tro-plating, it  is  preferable  to  use  batteries  with  two  acids, 
namely,  dilute  sulphuric  acid  and  concentrated  nitric  acid,  or 
chromic  acid. 

In  Stoehrer's  construction  (Fig.  15)  the  porous  clay  cup  is 
omitted,  the  massive  carbon  cylinders  K,  K,  etc.,  being  each 
provided  with  a  cavity  reaching  almost  to  the  bottom  which 

is  filled  with  sand  and  nitric  acid. 
The  contact  of  the  carbon  and  zinc 
cylinders  is  prevented  by  glass  beads 
imbedded  in  the  carbon  cylinders. 

Fig.  16  shows  a  plunge  battery 
manufactured  by  Dr.  G.  Langbein 
&  Co.,  the  details  of  which  will  be 
readily  understood  without  further 
description.  The  zinc  plates  dip  in 
the  diaphragms,  which  are  filled 
with  a  mixture  of  26  Ibs.  of  water 
and  2  Ibs.  of  sulphuric  acid  free 
from  arsenic,  in  which  2f  ozs.  of 
amalgamating  salt  have  previously 
been  dissolved.  The  carbon  plates 
dip  into  the  glass  vessels,  which 
contain  a  solution  of  commercial 
crystallized  chromic  acid  in  the  pro- 
portion of  1  part  acid  to  5  water. 
In  place  of  this  pure  chromic  acid 
the  following  mixture  may  also  be 
used :  Water  10  parts  by  weight, 

sodium  dichromate  1.5  parts  by  weight,  pure  sulphuric  acid 
of  66°  Be\  5  parts  by  weight. 

This  solution  shows  no  inclination  towards  crystallization. 
In  the  illustration  only  two  cells  are  combined  to  a  battery, 
but  in  the  same  manner  a  plunge  battery  of  four  or  eight 


SOURCES    OF    CURRENT. 


87 


FIG  17. 


cells  may  be  constructed,  the  separate  cells  of  which  may 
all  be  coupled  parallel,  as  well  as  one  after  the  other,  and  in 
mixed  groups. 

Bichromate  cell.  For  temporary  use,  for  instance  by  gold- 
workers  and  others ;  for  gilding  or  silvering  small  articles,  the 
bottle-form  of  the  bichromate  cell  (Fig.  17)  may  be  advantage- 
ously employed.  In  the  bottle  A  two  long  strips  of  carbon 
united  above  by  a  metallic  connection  are 
fastened,  parallel  to  one  another,  to  a  vul- 
canite stopper,  and  are  there  connected 
with  the  binding-screw  ;  these  form  the  neg- 
ative element,  and  pass  to  the  bottom  of  the 
bottle.  Between  them  is  a  short,  thick  strip 
of  zinc  attached  to  a  brass  rod  passing 
stiffly  through  the  'center  of  the  vulcanite 
cork,  and  connected  with  the  binding-screw. 
The  zinc  is  entirely  insulated  from  the 
carbon  by  the  vulcanite,  and  may  be  drawn 
out  of  the  solution  by  means  of  the  brass 
rod  as  soon  as  the  services  of  the  cell  are 
no  longer  required. 

Coupling  cells.     According  to  the  laws  of 
Ohm,    previously    discussed,    the    current- 
strength  J  of  a  cell  is  equal  to  its  electro- 
motive force  E  divided  by  the  sum  of  the  internal  resistance 
w  and  the  external  resistance  wi : 


W  +  WI 

By  now  combining  several  such  cells,  say  n  cells,  to  a  bat- 
tery, the  electro-motive  force  of  the  latter  will  become  n.E, 
but  the  internal  resistance  n.w,  and  with  the  same  closed  cir- 
cuit as  the  single  cell  had,  the  external  resistance  wi  will  not 
increase.  Hence  the  current-strength  of  these  n  elements  has 
to  be  written 

n.E 


n.w. 


wi 


00  ELECTRO-DEPOSITION    OF    METALS. 

Now  it  is  evident  that,  if  a  definite  closed  circuit  with  a 
resistance  of  wi  be  given,  the  current-strength  cannot  be 
indefinitely  raised  by  increasing  the  number  of  n  elements. 
While  with  an  increase  in  the  number  of  n  elements,  the  electro- 
motive force  to  be  sure  grows  as  many  n  times,  the  internal 
resistance,  w,  also  grows,  so  that  finally  the  value  wi  which 
remains  the  same  disappears  for  the  resistance  nw  which  in- 
creases n-times.  Thus  the  current-strength  approaches  more 
and  more  the  limit  of  value 

nE  _=  E 
nw        w 

On  the  other  hand,  the  effect  can  neither  be  increased  at  will 
by  enlarging  the  surface  of  the  pair  of  plates  or  decreasing  the 
conducting  resistance  of  the  fluid  in  a  given  number  of  cells. 
Because  if  wi — the  external  resistance — is  large  enough  so 
that  the  internal  resistance  nw  may  be  disregarded,  the  current- 

Tj> 

strength  approaches  more  and  more  the  value  — 

wi 

Hence,  it  follows  that  the  enlargement  of  the  surface  of  the 
exciting  pair  of  plates  produces  an  increase  in  the  current-strength 
only  when  the  external  resistance  in  the  closed  circuit  is  small  in 
proportion  to  the  internal  resistance  of  the  battery. 

If  we  now  apply  the  results  of  the  above  explanations  to 

FIG.  18. 


practice,  we  find  that  the  cells  may  be  coupled  in  various 
ways  according  to  requirement. 

1.  If,  for  instance,  four  Bunsen  cells  (carbon-zinc)  are 
coupled  one  after  another  in  such  a  manner  that  the  zinc  of  one 
cell  is  connected  with  the  carbon  of  the  next,  and  so  on  (Fig. 
18),  the  current  passes  four  times  in  succession  through  an 


SOURCES    OF    CURRENT. 


equally  large  layer  of  fluid,  in  consequence  of  which  the  in- 
ternal resistance  (4w),  is  four  times  greater  than  that  of  a 
single  cell,  while  the  resistance  of  the  closed  circuit  (wi),  re- 
mains the  same.  Hence,  while  the  current-strength  is  thereby 
not  increased,  the  electro-motive  force  is,  and  for  this  reason 
this  mode  of  coupling  is  called  the  union  or  coupling  of  the 
elements  for  electro-motive  force  or  tension. 

FIG.  19. 


FIG.  20. 


2.  By  connecting  four  cells  alongside  of  each  other,  i.  e.,  all 
the  zinc  plates  and  all  the  carbon  plates  one  with  another 
(Fig.  19),  the  current  simultaneously  passes  through  the  same 
layer  of  fluid  in  four  places ;  the  internal  resistance  of  the 
battery  is  therefore  the  same  as  that  of 

a  single  cell,  and  since  the  surface  of  ^ 
the  plates  is  four  times  as  large  as 
that  of  a  single  cell,  the  quantity  of 
current  is  increased  by  this  mode  of 
coupling.  This  is  called  coupling  .for 
quantity  of  current,  or  coupling  in  parallel. 

3.  Two  cells  may,  however,  be  con- 
nected for  electro-motive  force  or  ten- 
sion, and  several  such  groups  coupled 
alongside  of  each  other,  as  shown  in 
Fig.  20,  whereby,  according  to  what 

has  above  been  said,  the  electro-motive  force,  as  well  as  the 
current-strength,  is  increased.  This  mode  of  connection  is 
called  mixed  coupling,  or  group  coupling. 

According  to  the  resistance  of  the  bath  as  the  exterior  closed 
circuit,  and  according  to  the  surfaces  to  be  plated,  the  electro- 


'90 


ELECTRO-DEPOSITION    OF    METALS. 


plater  may  couple  his  cells  in  either  way.  We  will  here  only 
mention  the  proposition  deduced  from  Ohm's  law,  that  a  num- 
ber of  voltaic  cells  yield  the  maximum  of  current-quantity  when 
they  are  so  arranged  that  the  internal  resistance  of  the  battery  is 
equal  to  the  resistance  in  the  closed  circuit.  Hence,  when  oper- 
ating with  baths  of  good  conductivity  and  slight  resistance, 
for  instance,  acid  copper  baths,  silver  cyanide  baths,  etc.,  with 
a  slight  distance  between  the  anodes  and  the  objects,  and  with 
a  large  anode-surface,  it  will  be  advantageous  to  couple  the 
elements  alongside  of  each  other  for  quantity.  However,  for 
baths  with  greater  resistance  and  with  a  greater  distance  of 
the  anodes  from  the  objects,  and  with  a  smaller  anode  surface, 
it  is  best  to  couple  the  elements  one  after  the  other  for  electro- 
motive force  or  tension. 

B.  THERMO-ELECTRIC  PILES. 
Although  thermo-electric  piles  are  only  used  in  isolated 

FIG.  21. 


•cases  for  electro-plating  operations,  for  the  sake  of  complete- 
ness their  nature  and  best-known  forms  will  be  briefly  men- 
tioned. 

Professor  Seebeck,  of  Berlin,  observed  in  1823,  that  elec- 


SOURCES    OF    CURRENT. 


91 


tricity  is  developed  when  the  soldered  joints  of  two  metals  are 
unequally  heated ;  hence,  while  electricity  can  be  converted 
into  heat,  heat  vice  versa  can  be  converted  into  electricity. 

Noe's  thermo-electric  pile  (Fig.  21)  consists  of  a  series  of 
small  cylinders  composed  of  an  alloy  of  36J  parts  of  zinc  and 
62J  parts  of  antimony  for  the  positive  element  and  stout  Ger- 
man silver  as  the  negative  element.  The  soldering  consists 
of  tin.  The  junctions  of  the  elements  are  heated  by  small  gas 
jets,  and  the  alternate  junctions  are  cooled  by  the  heat  being 
conducted  away  by  large  blackened  sheets  of  thin  copper.  A 
pile  of  twenty  pairs  has  an  electro-motive  force  of  1.9  volts. 

Clamond's  thermo-electric  pile  (Fig.  22)  also  consists  of  a  zinc- 

FIG.  22. 


antimony  alloy,  but  in  place  of  German  silver,  ordinary 
tinned  sheet  iron  is  employed.  To  insure  good  contact  be- 
tween the  two  metals,  a  strip  of  tin-plate  is  bent  into  a  narrow 
loop  at  one  end.  This  portion  is  then  placed  in  a  mould  and 
the  melted  alloy  poured  around  it,  so  that  it  is  actually 
imbedded  in  the  casting.  The  pile  shown  in  the  illustration 
consists  of  five  series,  one  placed  above  the  other.  Each  series 
has  ten  elements  grouped  in  a  circle,  and  is  insulated  from  the 


92 


ELECTRO-DEPOSITION    OF    METALS. 


succeeding  series  by  asbestos  disks.  With  the  consumption  of 
about  6J  cubic  feet  of  gas  per  hour,  such  a  pile  deposits  0.7  oz. 
of  copper,  which  corresponds  to  an  intensity  of  about  17 
amperes. 

Gulcher's  thermo-electric  pile,  invented  in  1890,  is  shown  in 
Fig.  23.  It  is  arranged  for  gas-heating,  and  with  a  constant 
supply  of  gas  requires  a  pressure-regulator.  The  negative 
electrodes  consist  of  nickel,  and  the  positive  electrodes  of  an 
antimony  alloy,  the  composition  of  which  is  kept  secret.  The 
negative  nickel  electrodes  have  the  form  of  thin  tubes  and  are 
secured  in  two  rows  in  a  slate  plate,  which  forms  the  termina- 
tion of  a  gas  conduit  with  a  U-shaped  cross-section  beneath  it. 
Corresponding  openings  in  the  slate  plate  connect  the  nickel 

FIG  23. 


tubes  with  the  gas  conduit,  the  latter  being  connected  by  means 
of  a  rubber  tube  with  the  pipe  supplying  the  gas.  Thus  the 
gas  first  passes  into  the  conduits,  next  into  the  nickel  tubes,  and 
leaves  the  latter  through  six  small  holes  in  a  soapstone  socket 
screwed  in  the  end  of  each  tube.  On  leaving  these  sockets  the 
gas  is  ignited  and  the  small  blue  flames  heat  the  connecting 
piece  of  the  two  electrodes.  This  connecting  piece  consists  of 
a  circular  brass  plate  placed  directly  over  the  soapstone  socket. 
One  end  of  it  is  soldered  to  the  nickel  tube,  while  the  other 
end,  towards  the  top,  is  in  a  socket  in  which  are  east  the  posi- 
tive electrodes.  The  latter  have  the  form  of  cylindrical  rods  with 
lateral  angular  prolongations.  To  the  ends  of  these  prolonga- 


SOURCES    OF    CURRENT.  93 

tions  are  soldered  long  copper  strips  secured  in  notches  in  the 
slate  plate.  They  serve  partially  for  cooling  off  and  partially 
for  connecting  the  couples.  For.ihe  latter  purpose  each  cop- 
per strip  is  connected  by  a  short  wire  with  the  lower  end  of  the 
nickel  tube  belonging  to  the  next  couple.  When  the  pile  is  to 
be  used,  the  gas  is  ignited  in  one  place,  the  ignition  spreading 
rapidly  through  the  entire  series  of  couples.  In  about  10  min- 
utes the  junctions  of  the  metals  have  attained  their  highest 
temperature  and  the  pile  its  greatest  power,  which,  with  a  con- 
stant supply  of  gas5  remains  unchanged  for  days  or  weeks. 

In  view  of  the  conversion  of  the  heat  produced  by  the  com- 
bustion of  the  gas  into  electricity,  the  useful  effect  of  the 
thermo  electric  pile  can  be  considered  only  a  very  slight  one. 
One  cubic  meter  of  ordinary  coal-gas  produces  on  an  average 
5200  heat-units,  hence  200  litres  per  hour  referred  to  one 
second  i-eVlh  5200  =  0.20  heat-unit.  These  correspond  to 
1208  volt-amperes,  1  volt-ampere  being  equal  to  0.00024  heat- 
unit.  Hence,  in  Giilcher's  thermo-electric  pile,  which  of  all 
known  thermo-piles  produces  the  greatest  useful  effect,  not 
much  more  than  1  per  cent,  of  heat  is  utilized  in  the  entire 
circuit,  and  about  J  per  cent,  in  the  outer  circuit. 

Although  thermo-electric  piles  may  be,  and  are  occasionally, 
used  for  electro-plating  operations,  they  cannot  compete  with 
dynamo-electric  machines  driven  by  steam,  which  as  regards 
the  consumption  of  heat  are  at  least  five  times  more  effective. 
They  can  only  be  used  in  place  of  voltaic  batteries,  having 
the  advantage  of  being  more  convenient  to  put  in  operation, 
more  simple,  cleanly,  odorless,  and  requiring  less  time  for 
attendance.  But,  on  the  other  hand,  their  original  cost  is 
comparatively  large,  it  being  ten  to  twenty  times  that  of 
Bunsen  cells. 

C.  DYNAMO-ELECTRIC  MACHINES. 

While  in  the  voltaic  cells,  chemical  energy  is  converted 
into  electric  energy,  and  in  the  thermo-piles,  heat  into  elec- 
tricity, in  the  dynamo-electric  machine  a  conversion  of  me- 
chanical energy  into  electrical  energy  takes  place. 


94 


ELECTRO-DEPOSITION    OF    METALS. 


Fundamental  principle  of  dynamo-electric  machines.  In  the 
dynamo-electric  machines  the  generation  of  the  current  results 
from  induction,  and  the  fundamental  principle  of  such  a 
machine  is  as  follows  : 

Suppose  an  iron  magnet  frame  M,  formed  of  a  powerful 
horse-shoe  magnet,  which  is  provided  with  two  cylindrically- 
turned  planes,  and  concentrically  fixed  to  these  planes,  a 
cylinder  A,  built  up  of  discs  of  soft  iron  as  shown  in  Fig.  24. 

FIG.  24. 


art. 


Lines  of  force  running  in  the*  direction  from  the  north  pole 
to  the  south  pole  permeate  the  soft-iron  cylinder.  If  in  the  air- 
space between  the  north  pole  of  the  magnet  and  the  cylinder, 
a  copper  wire,  indicated  in  the  illustration  by  a  small  circle, 
be  introduced,  and  moved  in  such  a  manner  that  it  cuts  the 
lines  of  force  flowing  from  the  north,  pole  through  the  air- 
space to  the  cylinder,  a  current  is  induced,  and  a  certain 
electro-motive  force  appears  at  the  ends  of  the  wire.  By 
moving  the  left-hand  wire  in  the  direction  indicated  by  the- 


SOURCES   OF    CURRENT.  95. 

arrow,  the  current,  according  to  the  hand  rule  illustrated  by 
Fig.  4  will  flow  away  from  the  observer  into  the  plane  of  the 
illustration,  and  by  moving  the  right-hand  wire  in  the  direc- 
tion of  the  arrow,  out  from  the  plane  of  the  illustration  to- 
wards the  observer. 

Instead  of  moving  the  wire  in  the  air-space,  it  may  also  be 
insulated  from  the  soft-iron  cylinder  and  secured  to  it.  If  now 
the  cylinder  be  moved  around  its  axis,  the  wire  cuts  the  lines 
of  force  in  exactly  the  same  manner  as  in  its  motion  in  the 
air-space,  the  effect  remaining  the  same.  If  several  wires,  one 
alongside  the  other,  be  secured  upon  the  cylinder,  a  corre- 
sponding electro-motive  force  will  be  produced  on  the  ends  of 
each  wire,  the  positive  poles  of  the  wires  being  then  on  one 
side,  say  the  front,  of  the  pole  pieces,  while  the  negative  poles 
of  all  the  wires  lie  upon  the  other,  the  rear,  side.  If  now  the 
wires  be  connected  one  with  the  other,  so  that,  when  the 
cylinder  is  revolved,  a  positive  pole  is  always  attached  to  a 
negative  pole,  the  electro-motive  force  is  raised  in  the  same 
degree  as  the  number  of  wires  coupled  one  after  the  other  (in 
series)  increases. 

These  wires  fastened  upon  the  iron  body  are  called  windings,. 
and  the  term  armature  is  applied  to  an  iron  body  furnished 
with  such  windings. 

The  electro-motive  force  generated  in  the  windings  is  the 
greater,  the  greater  the  velocity  with  which  the  wires,  or  con- 
ductor forming  the  windings,  are  moved  through  the  mag- 
netic field.  If  the  length  of  the  conductors  be  increased  by 
enlarging  the  windings,  and  the  velocity  with  which  the 
armature  moves  remains  the  same,  the  electro-motive  force 
generated  in  the  conductor  is  proportional  to  the  length  of  the 
latter.  If,  on  the  other  hand,  the  magnetic  field  be  strength- 
ened, thus  increasing  the  lines  of  force  cut  by  the  conductor 
during  its  motion,  and  the  velocity  with  which  the  conductor 
moves,  as  well  as  its  length,  remains  the  same,  the  electro- 
motive force  is  proportional  to  the  number  of  lines  of  force, 
reaching  its  greatest  value  when  the  lines  of  force  are  perpen- 
dicularly cut  by  the  conductor. 


ELECTRO-DEPOSITION    OF    METALS. 


Separate  parts  of  the  dynamo- electric  machine.  The  frame. 
The  production  of  the  magnetic  field  has  for  a  long  time  been 
-effected  by  electro-magnets.  The  field  magnets  of  gray  cast- 
iron  or  cast-steel  are  cast  in  one  piece  with  the  gray  cast-iron 
•or  cast-steel  frame,  or  screwed  to  it.  These  field  magnets  are 
wrapped  with  wire  through  which  the  current,  by  which  they 
are  magnetically  excited,  is  conducted.  This  winding  is 
•called  magnet  winding  or  field  winding.  According  to  the 
number  of  field  magnets,  a  distinction  is  made  between  two- 
polar,  four-polar,  six-polar  and  multipolar  machines. 

Fig.  25  shows  a  two-polar,  and  Fig.  26  a  four-polar  type  of 


FIG.  25. 


FIG.  26. 


dynamo  of  the  firm  of  Dr.  G.  Langbein  &  Co.,  Leipsic,  Ger- 
many. The  frame  and  foundation  plate  of  soft  cast-iron  are 
•cast  in  one  single  casting ;  only  in  larger  types  is  the  frame 
secured  to  the  foundation  plates  by  screws. 

For  the  production  of  the  magnetic  field,  the  current  was 
formerly  conducted  from  another  source  of  electricity  into  the 
magnet  windings,  but  since  the  discovery  of  the  dynamo- 
•electric  principle  by  W.  v.  Siemens,  the  electric  current  gener- 
ated in  the  armature  is  utilized  for  the  excitation  of  the  mag- 
netic field.  The  dynamo-electric  principle  is  based  upon  the 
following :  Lines  of  force,  few  in  number,  are  present  from  a 
previous  excitation  in  every  magnet  frame,  and  this  is  called 


SOURCES    OF    CURRENT.  97 

remanent  magnetism  (see  p.  13).  In  revolving  the  armature 
the  existence  of  this  small  number  of  lines  of  force  suffices  for 
the  induction  of  a  weak  current  which  is  partly  conducted 
through  the  magnet  winding,  the  magnetic  field  being  thereby 
intensified.  The  effect  of  this  is  the  generation  of  currents  of 
considerably  greater  power  in  the  armature,  which  again  bring 
about  an  increase  in  the  current-strength  in  the  magnet  wind- 
ing, until  the  frame  is  saturated  with  -lines  of  force.  This 
process  is  called  self-excitation,  while  the  term  foreign  or  sepa- 
rate excitation  has  been  applied  to  it  when  the  magnetic  field 
is  excited  by  another  source  of  electricity. 

Armature  or  inductor.  It  has  already  been  mentioned  that 
the  armature  consists  of  a  cylindrical  iron  body  and  the  wind- 
ings wrapped  around  it.  The  iron  body  cannot  be  made  of  one 
piece  because  rotatory  currents  would  be  formed  in  it,  which 
heat  the  iron  very  much,  and  cause  a  loss  of  -current.  Hence 
the  body  of  the  armature  is  built  up  of  thin,  soft  sheet-iron 
discs  insulated  one  from  the  other  by  discs  of  paper.  The 
discs  are  firmly  pressed  upon  the  core  of  the  armature  and 
secured  by  t  screws,  while  the  core  of  the  armature  itself  is 
wedged  upon  the  shaft  by  means  of  a  wedge. 

According  to  the  manner  in  which  the  wire  windings  are 
laid  around  the  armature-core,  a  distinction  is  made  between 
•a  ring  armature  and  a  drum  armature. 

In  the  ring  armature  the  wire  windings  are  wrapped  in  a 
continuous  spiral  around  the  armature- core,  it  being  necessary 
for  the  latter  to  have  a  wide  bore  in  the  center  through  which, 
in  wrapping,  the  conducting  wire  may  be  carried.  Fig.  27 
represents  a  scheme  of .  such  ring-winding.  JVand  S  are  the 
two  field  magnets  of  the  frame.  Every  two  of  the  continuous 
wire  windings  represent  a  coil,  and  from  the  point  where  the 
end  of  one  coil  is  connected  with-  the  commencement  of  the 
next  coil  a  conducting  wire  branches  off  to  the  collector. 
According  to  what  has  above  been  said,  induction  is  greatest 
when  the  windings  of  the  wire  cut  the  lines  of  force  at  a  right 
•angle,  this  being  the  case  when  the  windings  are  directly 
7 


98 


ELECTRO-DEPOSITION    OF    METALS. 


under  the  poles.  In  revolving  the  armature  from  0°  to  90°, 
the  generation  of  current  decreases,  from  90°  to  180°  it  de- 
creases, from  180°  to  270°  it  increases  in  a  reverse  sense,  and 
from  270°  to  300°  it  again  decreases.  Thus,  currents  flowing 
alternately  in  opposite  directions,  the  so-called  alternating 
currents  are  generated,  and  their  conversion  into  constant 

FIG.  27. 


0. 


currents  of  uniform  direction  is  effected  by  the  commutator. 
At  0°  and  at  180°,  the  generation  of  current  is  equal  to  0, 
and  at  these  points  the  current  changes  its  direction  ;  the  line 
0°  to  180°  is  called  the  neutral  zone. 

In  the  drum  armature  the  conducting  wires  are  wound  upon 
the  armature-core  parallel  to  its  axis,  carried  on  the  faces  of 
the  core  around  the  core-shaft,  and  the  ends  of  every  two  coils 


SOURCES    OF    CURRENT. 


99 


lying  alongside  each  other  on  a  face  are  connected,  one  with 
the  other,  and  with  a  segment  of  the  commutator. 

Fig.  28  shows  the  drum  winding  viewed  from  the  side  of 
the  commutator.  Each  coil  is  only  indicated  by  a  single  wire 
winding,  and  therefore  8  coils  are  shown.  The  full  lines' 
indicate  the  connection  of  the  coils  upon  the  commutator-side 

FIG.  28. 


and  with  the  commutator,  and  the  dotted  lines,  the  coil-con- 
nections upon  the  opposite  face. 

What  has  been  said  in  regard  to  the  intensity  of  induction 
in  ring-armatures  applies  also  to  drurn-armatures. 

The  chief  difference  between  the  modes  of  winding  consists 
in  more  wire  being  required  for  ring  winding,  because  wires 


100  ELECTRO-DEPOSITION    OF    METALS. 

run  on  the  faces  as  well  as  in  the  interior  of  the  bore,  which 
•are  of  no  importance  as  regards  the  generation  of  the  current 
'by  "induction,  but,  on  the  one  hand,  materially  increase  the 
weight  of  the  armature,  and,  on  the  other,  enlarge  the  resist- 
ance. As  regards  these  points,  drum-winding  has  much  in  its 
favor,  and  it  has  the  further -advantage  that  the  armature-core 
•can  be  provided,  parallel  to  its  axis,  with  grooves  or  slots  for 
the  reception  of  the  windings,  they  being  thus  better  protected 
from  injury,  and  the  effect  of  centrifugal  force  can  in  a  suit- 
able manner  be  prevented  by  bands.  In  such  armatures,  even 
when  equipped  with  thick  copper  wires  or  flat  copper  bands, 
scarcely  any  rotatory  currents  are  generated,  because  the  slots 
are  but  slightly  permeated  with  lines  of  force,  the  latter  run- 

FIG.  29. 


ning  rather  around  the  copper  wires  through  the  iron.  How- 
ever, the  chief  advantage  of  such  an  armature  consists  in  that 
the  air-space  between  armature  and  magnet-pole  can  be  less 
than  in  armatures  with  windings  not  placed  in  slots,  because 
the  space  occupied  by  the  winding  of  such  so-called  smooth 
armatures  has  to  be  considered  as  an  air-space  and  offers  the 
greater  magnetic  resistance.  Hence  for  armatures  furnished 
with  slots,  the  number  of  ampere-windings  may  be  less  than 
for  smooth  amatures.  Fig.  29  shows  a  slotted  armature  of  a 
dynamo  constructed  by  the  firm  of  Dr.  G.  Langbein  &  Co.,  in 
which  the  conductors  consist  of  flat  copper  rods,  connected  on 
the  faces  by  bent  copper  bands  called  evolvents. 

Commutator.     This  is  a  cylindrical  body  built   up  of  seg- 
ments and  fastened  to  the  armature-shaft.      It  is  insulated 


SOURCES    OF    CURRENT.  101 

with  mica.  The  segments  consist  of  copper,  tombac,  or  brass 
and  are  insulated  from  each  other  as  well  as  from  the  com- 
mutator frame,  i.  e.,  the  iron  body.  The  commutator  has  as 
many  segments  as  the  armature  has  coils,  and  every  point  of 
junction  of  two  coils  is  intimately  connected  by  means  of 
copper  with  a  segment.  The  function  of  the  commutator 
consists  in  converting  the  alternating  currents  of  the  windings 
generated  by  induction  into  constant  currents  of  uniform 
direction.  As  seen  from  Fig.  27,  currents  of  opposite  direc- 
tions flow  in  each  half  of  the  windings  of  the  ring-armature. 
If  now  sliding  contacts  be  placed  on  the  commutator  on  the 
points  of  the  neutral  zone,  the  current  of  one-half  of  the  wind- 
ings is  carried  along  as  positive  current  by  one  of  the  sliding 
contacts,  and  the  negative  current  of  the  other  half  by  the 
other  sliding  contact.  The  armature  winding  is  divided  into 
two  halves  by  the  brushes  which  are  coupled  parallel  to  each 
other.  The  induction  of  each  separate  coil  corresponds  to  its 
position  for  the  time  being  in  the  magnetic  field,  the  sum  of 
the  induction  of  all  the  coils  in  one-half  of  the  armature  being 
equal  to  that  of  all  the  coils  in  the  other  half,  but  as  previ- 
ously shown,  the  direction  of  the  current  in  both  halves  is 
different. 

Brushes.  The  function  of  the  brushes  is  to  take  off  the  cur- 
rent from  the  commutator.  For  such  dynamo-electric  ma- 
chines as  here  come  into  question,  the  brushes  are  of  fine 
copper  or  brass  wire-gauze,  or  of  very  thin  metal-plate.  Car- 
bon brushes  are  often  used  for  dynamo-electric  motors. 

The  choice  of  material  for  the  brushes  depends  on  the  prop- 
erties of  the  material  of  the  commutator.  As  there  should  be 
as  little  wear  as  possible  of  the  commutator  by  the  brushes, 
the  material  used  for  the  latter  should  be  somewhat  softer 
than  that  for  the  former.  Copper  and  brass  gauze  brushes 
produce  by  their  wear  considerable  metallic  dust,  which  settles 
on  all  parts  of  the  machine,  as  well  as  on  the  armature  and, 
if  not  removed  by  frequent  blowing  out  with  a  pair  of  bellows, 
or  a  similar  instrument,  may  readily  cause  short-circuiting. 


102  ELECTRO-DEPOSITION    OF    METALS. 

Brushes  of  twisted,  thin  metal-plates  (Boudreaux  brushes)  do 
not  show  this  disagreeable  formation  of  dust,  and  cause  but 
little  wear  of  the  commutator,  rather  polishing  it.  They 
have,  however,  the  drawback  of  the  portions  bearing  on  the 
commutator  oxidizing  readily,  in  consequence  of  becoming 
heated  by  the  large  quantities  of  current.  This  oxidation  is 
not  removed  by  the  friction,  and  greater  resistance  is  thereby 
opposed  to  the  passage  of  the  current  from  the  commutator  to 
the  brushes.  This,  on  the  one  hand,  results  in  the  commu- 
tator and  brushes  becoming  strongly  heated  and,  on  the  other, 
causes  a  decrease  in  taking  off  the  current. 

The  bearing  surfaces  of  the  brushes  should  be  so  large  that 
no  heating  is  caused  by  the  passage  of  the  current,  which 
would  increase  to  a  considerable  extent  the  quantity  of  heat 
unavoidably  formed  by  the  friction,  and  be  a  disadvantage  as 
regards  the  useful  effect  of  the  dynamo. 

Brush-holders.  These  serve  for  securing  the  brushes  and 
should  hold  them  so  as  to  bear  with  an  even  pressure  upon 
the  commutator.  This  is  effected  by  metal  springs  by  means 
of  which  the  brush-frame,  which  carries  the  brush,  is  elas- 
tically  connected  with  the  portion  of  the  brush-holder  screwed 
to  the  bolt  of  the  brush-rocker. 

Brush-rocker.  This  serves  for  carrying  the  brush-holder, 
and  for  this  purpose  is  furni  shed  with  two  thick  copperbolts 
having  a  cross-section  corresponding  in  size  to  the  quantity  of 
current  to  be  conducted.  In  multi-polar  dynamos,  the  rockers 
are  equipped  with  as  many  bolts  as  there  are  poles.  These 
bolts  are  insulated  from  the  rocker  by  cases  of  a  good  insu- 
lating material,  and  secured  to  the  rocker  by  insulated  nuts. 

The  rocker  is  mounted  upon  the  turned  end  of  a  bearing, 
and  is  concentrically  movable  to  its  axis,  .so  that  by  turning 
it,  the  brushes  may  be  shifted  into  a  position  at  which  the 
dynamo  runs  with  the  least  sparking.  In  this  position  the 
brush  holder  is  kept  by  means  of  an  adjusting  screw. 

The  rocker  should  also  be  kept  free  from  metal  dust,  other- 
wise short-circuiting  may  readily  result. 


SOURCES    OF    CURRENT.  103 

The  other  parts  of  a  dynamo,  such  as  bearings,  cable,  etc., 
need  not  be  especially  referred  to,  and  it  only  remains  to  dis- 
cuss the  various  types  of 

Direct  current  dynamos.  If  the  whole  of  the  current  traverses 
the  coil  of  the  field  magnet,  the  dynamo  is  said  to  be  series 
wound;  or  if  a  portion  of  the  current  be  shunted  we  have  a 
shunt-wound  dynamo ;  or  finally  there  may  be  a  combination 
of  the  two  in  which  case  the  machine  is  a  compound  dynamo. 
Whatever  be  the  arrangement,  provided  the  volume  of  the 
copper  and  the  density  of  the  current  are  the  same,  the  same 
field  is  always  produced. 

Nearly  all  the  early  types  of  electric  dynamos  were  what  is 
known  as  "  series  wound  "  machines,  where  the  full  current  of 
the  armature  passed  through  the  field  coils.  These  machines 
had  the  very  serious  disadvantage  of  possessing  poor  regula- 
tion and  being  subject  to  frequent  reversal  of  current  direc- 
tion: The  plating  dynamos  on  the  market  to-day  are  what 
is  technically  known  as  "  shunt-wound "  and  "compound- 
wound  "  machines. 

In  a  shunt-wound  dynamo  the  field  magnet  coils  are  placed 
in  a  shunt  to  the  armature  circuit  so  that  only  a  portion  of 
the  current  generated  passes  through  the  field  magnet  coils, 
but  all  the  difference  of  potential  of  the  armature  acts  at  the 
terminals  of  the  field  circuit. 

In  a  shunt-wound  dynamo,  an  increase  in  the  resistance  of 
the  external  circuit  increases  the  electro-motive  force,  and  a 
decrease  in  the  resistance  of  the  external  circuit  decreases  the 
electro-motive  force.  This  is  just  the  reverse  of  the  series- 
wound  dynamo. 

In  a  shunt-wound  dynamo  a  continuous  balancing  of  the 
current  occurs.  The  current  dividing  at  the  brushes  between 
the  field  and  the  external  circuit  in  the  inverse  proportion  to 
the  resistance  of  these  circuits,  if  the  resistance  of  the  external 
circuit  becomes  greater,  a  proportionately  greater  current 
passes  through  the  field  magnets,  and  so  causes  the  electro- 
motive force  to  become  greater.  If,  on  the  contrary,  the  re- 


104  ELECTRO-DEPOSITION    OF    METALS. 

sistance  of  the  external  circuit  decreases,  less  current  passes 
through  the  field,  and  the  electro-motive  force  is  proportion- 
ately decreased.  Thus,  up  to  a  certain  degree,  a  shunt-wound 
dynamo  regulates  itself. 

Fig.  30  illustrates  a  two-pole  shunt-wound  dynamo,  and 
Fig.  31  a  two-pole  shunt-wound  dynamo  for  high  current- 
strengths. 

In  Fig.  30  the  frame  is  of  cast-steel  and  the  bearing  plates 
are  screwed  to  it.  In  Fig.  31  the  pillow-blocks  and  frame  are 
mounted  upon  a  common  cast-iron  plate. 

The  armature  is  of  the  slotted  drum   type  described   in 

FIG:  30. 


Fig.  29.  It  is  encompassed  by  two  strong  field  magnets 
arranged  in  vertical  position,  radially  opposite  one  to  the  other. 
The  ends  of  the  field  magnets  are  concentrically  turned  to  the 
armature  and  their  oblique  tapering  shape  prevents  the  jerky 
formation  or  interruption  of  the  current,  thus  rendering  possi- 
ble a  spa,rkless  taking-off  of  current  on  the  commutator.  The 
ends  of  the  armature  coils  are  soldered  to  the  copper  segments 
of  the  commutator,  loosening  of  the  connecting  points  being 
thus  excluded,  as  is  invariably  the  case  with  wires  secured  by 
means  of  screws  to  the  commutator.  An  abundance  of  cop- 
per cross-sections  being  used,  the  degree  of  efficiency  of  the 
dynamo  is  an  excellent  one.  To  decrease  friction,  the  portions 


SOURCES    OF    CURRENT.  105 

of  the  steel  armature  shaft  which  run  in  the  journal  boxes  of 
phosphor-bronze,  as  well  as  the  latter  themselves,  are  highly 
polished.  The  bearings  are  furnished  with  automatic  ring- 
lubrication.  By  reason  of  the  use  of  large  cross-sections  of 
copper  upon  the  armature  and  magnet  winding,  the  number 
of  revolutions  is  a  moderate  one,  and  consequently  the  con- 
sumption of  power  and  wear  of  the  bearings  are  slight. 

Dynamos  which  yield  high  current-strengths  are  furnished 
with  two  commutators  to  avoid  overloading  and  consequent, 
excessive  heating  of  a  single  commutator. 

FKJ.  31. 


A  compound  wound  dynamo  has  two  distinct  windings  on 
its  field  magnet — one  of  the  very  many  turns  of  fine  wire, 
called  the  shunt  winding,  and  another  known  as  the  series 
winding,  which  latter  consists  of  a  number  of  turns  of  heavier 
gauge  wire.  The  series  winding  is  in  series  with  the  vats  or 
external  circuit.  The  current  that  is  used  in  the  vats,  pass- 
ing through  this  winding,  increases  the  magnetism  of  the  field 
as  the  load  increases,  and  thus  the  drop  in  voltage,  which 
would  otherwise  occur  by  reason  of  the  increased  drop  in  the 
armature  winding  and  increased  magnetic  reaction  caused  by 
the  armature  current  is  provided  for. 


106  ELECTRO-DEPOSITION    OF    METALS. 

Fig.  32  shows  a  multi-polar  type  of  dynamo  manufactured 
by  The  Hanson  &  Van  Winkle  Co.,  Newark,  N.  J.  The 
frame  is  made  of  a  high-grade  cast  iron,  having  a  high  mag- 
netic permeability.  The  poles  are  made  of  soft  rolled  steel 
with  cast-iron  shoes.  Field  coils  are  of  insulated  copper  wire 
wound  compactly  by  machinery,  insuring  the  maximum 
ampere-turns  without  great  bulk.  The  whole  coil  is  properly 
insulated  and  protected  from  mechanical  injury. 

FIG.  32. 


The  armature,  Fig.  33,  is  of  the  toothed  type.  The  core  is 
built  up  of  thin  soft  steel  discs,  and  is  insulated  on  both  sides 
and  assembled  on  a  spider  constructed  to  insure  the  greatest 
amount  of  ventilation. 

The  armature  coils  are  made  in  a  form  and  perfectly  insu- 
lated. The  slots  in  which  the  coils  rest  are  also  insulated,  so 
that  there  is  no  chance  for  a  ground. 

The  segments  of  the  commutator  are  forged  from  pure  cop- 
per carefully  insulated  with  the  best  mica.  The  radials  from 
the  bars  are  so  set  that  a  steady  current  of  air  is  thrown  on 
the  commutator  and  brushes. 


SOURCES    OF    CURRENT. 


107 


The  bearings  are  self-aligning,  boxes  are  made  of  special 
bronze,  and  are  provided  with  large  oil-wells  and  automatic 
-oiling-rings. 

FIG.  33. 


This  machine  will  run  continuously  under  full  load  with  a 
rise  of  temperature  above  the  surrounding  atmosphere  not 


Fro.  34. 


exceeding  55°  F.  in  the  accumulator,  and  something  less  in 
windings. 


108  ELECTRO-DEPOSITION    OF    METALS. 

Fig.  34  shows  a  separately  excited  dynamo  of  the  multi- 
polar-type  manufactured  by  The  Hanson  &  Van  Winkle  Co., 
Newark,  N.  J.  It  is  a  very  popular  form  of  generator,  the* 
field  being  excited  from  an  external  circuit,  usually  110  or 
220  volts  D.  0.  The  capacity  is  4000  amperes  at  6  volts. 
The  commercial  efficiency  is  high,  86  per  cent. — the  electrical 
efficiency  averages  93  per  cent.  This  form  of  dynamo  is  fur- 
nished for  both  two  and  three  wire  systems  of  current  distribu- 
tion. The  frame  and  pole  pieces  are  of  steel.  For  the  frame 
a  special,  soft  grade  is  used,  having  a  high  magnetic  perme- 
ability. The  field  coils  are  made  of  insulated  copper  wire 
wound  compactly  by  machinery,  insuring  the  maximum 
ampere-turns  without  great  bulk.  The  whole  coil  is  properly 
'insulated  and  protected  from  mechanical  injury. 

The  great  advance  which  has  in  modern  times  been  made 
in  the  art  of  electro-plating,  is  largely  due  to  the  important 
improvements  that  have  been  made  in  the  construction  of 
dynamo-electric  machines,  by  which  mechanical  energy  gener- 
ated by  the  steam-engine  or  other  convenient  source  of  power 
may  be  directly  converted  into  electrical  energy.  Without 
dynamos  it  would  be  impossible  to  electro-plate  large  parts  of 
machines,  architectural  ornaments,  etc.,  which  are  thus  pro- 
tected from  the  influence  of  the  weather.  They  may  safely  be 
credited  with  having  called  into  existence  an  important  branch 
of  the  electro-plating  art,  viz.,  nickel-plating,  and  especially 
the  nickel-plating  of  zinc  sheets,  as  well  as  sheets  of  copper, 
brass,  steel,  and  tin,  which  would  have  been  impossible  if  the 
manufacturer  had  to  rely  upon  the  generation  of  the  electric 
current  by  batteries.  The  latter,  at  the  very  best,  are  trouble- 
some to  manage ;  they  only  give  out  their  full  power  when 
freshly  charged,  and  as  the  chemical  actions  upon  which  they 
rely  for  their  power  progress,  they  deteriorate  in  strength  and 
require  frequent  additions  of  acids  and  salts  to  be  freshly 
charged,  and  their  use  demands  constant  vigilance  arid  atten- 
tion. Even  when  working  on  a  small  scale,  it  is  cheapest  to 


SOURCES    OF    CURRENT. 


109 


procure  a  small  gas  or  other  motor  for  driving  a  small  dynamo, 
the  lathes,  and  grinding  and  polishing  machines. 

Most  cities  and  towns  are  now  supplied  with  electric  light 
from  central  stations,  and  thus  the  means  are  furnished  to 
smaller  plants  to  avail  themselves  of  the  use  of  electricity 
without  the  necessity  of  installing  their  own  source  of  power. 
From  such  central  stations  the  conductors  are  fed  with  cur- 
rents of  110  or  220  volts.  Hence  the  wires  from  the  power 
circuit  can  be  directly  connected  with  a  motor-generator,, 
which  is  constructed  for  the  respective  voltage  and  converts 

FIG.  35. 


the  supply  of  current  into  power,  driving,  for  instance,  a 
connecting  gear,  from  which  the  grinding  and  polishing 
machines,  as  well  as  a  dynamo  of  low  voltage,  are  impelled. 
The  dynamo  may  be  directly  connected  by  means  of  a  flexible 
or  rigid  coupling  to  the  motor-generator.  The  armature  of 
the  latter  may  also  be  directly  placed  upon  the  grinding  and 
polishing  shafts,  and  the  magnets  arranged  around  it,  so  that 
every  working  machine  becomes  a  motor-generator. 

Fig.  35  shows  a  150-ampere  motor-generator  set,  and  Fig. 
36,  a  4000-ampere  motor-generator  set,  manufactured  by  The 
Hanson  &  Van  Winkle  Co.,  Newark,  N.  J.  A  low  voltage 
dynamo  is  directly  connected  to  a  motor  of  suitable  size,  the 


110 


ELECTRO-DEPOSITION    OF    METALS. 


whole  outfit  being  mounted  on  a  substantial  iron  base.  There 
is  no  loss  of  power  as  in  the  case  when  belts  are  used,  so  the 
full  capacity  of  the  generator  is  available.  Jn  many  instances 
the  plating  dynamo  is  installed  some  distance  from  the  tank^ 
and  conductors  of  large  cross-sections  must  be  used  in  order 
that  there  may  be  no  drop  in  voltage  at  the  tanks.  Th  is,of 
course,  increases  the  cost  of  installation.  With  the  motor- 

FIG.  36. 


generator  set,  wires  from  the  power-circuit  can  be  brought  to- 
the  plating  room  and  the  outfit  can  be  set  up  near  the  tanks. 
These  outfits  are  made  in  all  sizes,  both  bipolar  generators,  as 
shown  in  the  illustration,  or  generators  of  the  multipolar  type 
being  used. 

To  enable  the  manufacturer  of  dynamos  to  suggest  the  most 
suitable  machine  the  following  data  should  be  submitted  to 
him: 

1.  Variety,  size,  and  number  of  the  baths  which  are  to  be 
fed  by  the  machine. 

2.  The  average  surface  of  the  articles  in  the  bath,  or  their 
maximum  surface,  and  the  metals  of  which  they  consist. 


SOURCES    OF    CURRENT.  Ill 

3.  Whether  at  one  time  many,  and  at  another  time  few,, 
articles  are  suspended  in  the  bath. 

4.  The  distance  at  which  the  machine  can  be  placed  from 
the  baths. 

5.  The  power  at  disposal. 

If  the  establishment  is  to  be  electrically-driven  by  a  motor- 
generator,  the  machines  which,  in  addition  to  the  dynamo, 
are  to  be  driven  by  the  motor-generator  should  be  mentioned, 
as  well  as  the  voltage  of  the  power-circuit  which  is  to  be  used 
as  a  supply  of  electricity. 

D.  SECONDAKY  CELLS  (ACCUMULATORS). 

In  the  theoretical  part  of  this  treatise,  the  polarization- 
current  has  been  referred  to.  Although  the  polarization  of 
metal  plates  for  the  production  of  secondary  currents  had 
previously  been  employed  by  Bitter,  the  construction  of  prac- 
tically useful  accumulators  was  first  accomplished  by  Plante. 
He  found  that  lead  plates  dipping  in  dilute  sulphuric  acid 
were  specially  well  'adapted  for  the  production  of  secondary 
currents,  and  he  arranged  the  accumulators  as  follows:  In  a 
square  glass  vessel  filled  with  10  per  cent,  sulphuric  acid  solu- 
tion, a  large  number  of  lead  plates  were  suspended  in  such  a 
way  that  all  plates  with  even  numbers,  2,  4,  6,  and  so  on,, 
were  electrically  connected  one  with  the  other,  while  the  plates 
with  uneven  numbers,  hence,  1,  3,  5,  and  so  on,  were  also  in 
contact  with  each  other.  Between  the  separate  plates  dipping 
in  the  acid  was  sufficient  space  to  prevent  them  from  touch- 
ing one  another.  One  series  of  the  plates  served  as  positive, 
and  the  other  as  negative,  electrodes.  Now  by  conducting  an 
electric  current  through  the  plates,  lead  peroxide  is  formed 
upon  the  positive  electrodes,  and  by  interrupting  the  current 
and  combining  the  series 'of  electrodes  with  each  other,  the 
peroxide  is  reduced  to  metallic  lead,  and  the  negative  lead 
plates  are  oxidized,  whereby  an  electric  discharge  takes  place, 
the  secondary  or  accumulator-current  passing  through  the 
metallic  connection  of  the  series  of  plates  from  the  peroxide 
to  the  lead  plates. 


112  ELECTRO-DEPOSITION    OF    METALS. 

Hence,  in  charging,  a  conversion  of  electrical  energy  into 
chemical  energy  takes  place  and,  in  discharging,  a  recon- 
version of  the  chemical  energy  into  electric  energy.  A  large 
quantity  of  the  latter  can  therefore  accumulate  in  the  cells, 
whence  the  term  accumulator  is  derived. 

For  the  production,  in  the  above-described  manner,  of  cur- 
rents of  high  power  and  longer  duration,  the  plates  have  to  be 
suspended  as  closely  together  as  possible  without  danger  of 
contact,  in  order  to  decrease  the  internal  resistance  of  the 
element  as  far  as  practicable,  and  also  to  increase  the  quantity 
of  lead  peroxide. 

However,  the  formation  of  the  layer  of  lead  peroxide  upon 
the  lead  plates  of  Plante's  accumulator  was  a  slow  process,  and 
for  this  reason  Faure  used  lead  grids.  The  square  openings 
in  the  negative  plates  are  filled  with  a  paste  of  litharge  and 
sulphuric  acid,  and  the  positive  plates  with  one  of  minium 
and  sulphuric  acid.  The  current  reduces  the  litharge  and 
peroxidizes  the  minium. 

Plante  showed  that  accumulators  /orw'by  usage — that  is  to 
say,  that  up  to  a  certain  point  their  capacity  is  greater  the 
more  frequently  they  have  been  charged  and  discharged.  By 
repeated  oxidation  and  deoxidation  the  lead  acquires  a  spongy 
structure,  and  gradually  a  large  mass  of  metal  takes  part  in 
the  reaction.  The  formation  is  accelerated  by  immersing  the 
fresh  plate  for  a  day  or  two  in  nitric  acid  diluted  with  its  own 
volume  of  water. 

Chemical  processes  in  the  accumulator.  Regarding  these  pro- 
cesses, several  theories  have  been  advanced,  for  instance,  by 
Elbs,  Liebenow,  and  others,  but  it  has  not  yet  been  definitely 
settled  which  of  these  views  is  correct.  There  can,  however, 
be  no  doubt  that  the  lead  sulphate  which  is  formed  by  the 
action  of  the  sulphuric  acid  upon  the  lead,  plays  the  principal 
role,  in  so  far  as  the  charging  and  discharging  of  the  accumu- 
lator are  effected  only  by  the  decomposition  and  subsequent 
reformation  of  the  lead  sulphate. 

Elb's  theory  is  as  follows :  As  lead  is  bivalent  and  quadri- 


SOURCES    OF    CURRENT.  113 

valent,  after  the  decomposition  of  the  lead  sulphate  to  lead 
and  sulphuric  acid,  the  latter  combines  with  the  lead  sulphate, 
which  remains  undecomposed,  to  lead  disulphate.  This  for- 
mation of  lead  disulphate  must  chiefly  take  place  on  the  posi- 
tive electrodes,  since  the  anion  (the  sulphuric  acid  residue) 
migrates  to  the  positive  pole,  and  by  the  action  of  the  water 
the  lead  disulphate  is  decomposed  to  lead  peroxide  and  free 
sulphuric  acid. 

If,  therefore,  the  current  taken  from  a  dynamo  be  conducted 
into  the  electrodes  of  an  accumulator,  so  that  the  positive 
plates  are  connected  with  the  +  pole  of  the  dynamo  and  the 
negative  plate  with  the  —  pole,  decomposition  of  sulphuric 
acid  takes  place,  the  hydrogen  migrating  to  the  negative  elec- 
trode, and  the  sulphuric  acid  residue  to  the  positive  electrode. 
On  the  latter,  the  sulphuric  acid  residue  forms  first  of  all  with 
•the  lead,  lead  sulphate  according  to  the  following  equation  : 

,       S04     +     Pb     =     PbS04 

Sulphuric  acid  residue.     Lead.          Lead  sulphate. 

By  the  influx  of  additional  S04-ions,  this  lead  sulphate  is 
'converted  into  lead  disulphate  : 

S04     +     PbS04     =     Pb(S04)2 

Sulphuric  acid  residue.     Lead  sulphate.      Lead  disulphate. 

However,  since  the  formation  of  the  lead  disulphate  does 
not  take  place  quantitatively,  S04-ions  are  simultaneously  con- 
verted into  sulphuric  acid,  H2S04,  oxygen  being  separated  in 
the  form  of  gas. 

According  to  Elbs,  lead  disulphate  decomposes  with  water 
to  lead  peroxide  and  sulphuric  acid  according  to  the  following 
equation  : 

Pb(S04)2     +     2H20     =     Pb02     +     2H2S04 

Lead  disulphate.  Water.  Lead  peroxide.     Sulphuric  acid. 

Thus,  if  the  current  be  interrupted,  we  have  lead  peroxide 
on  the  positive  electrode,  and  spongy  lead  reduced  by  hydro- 

8 


114  ELECTRO-DEPOSITION    OF   METALS. 

gen,  on  the  negative  electrode.  If  now  the  positive  electrodes 
be  connected  with  the  negative  electrodes  by  a  closed  wire,  a 
current  passes  through  this  wire  from  the  positive  lead  per- 
oxide electrodes  to  the  negative  lead  electrodes,  and  from  the 
latter,  through  the  electrolyte,  back  to  the  positive  electrodes. 

Thus  during  the  discharge,  the  spongy  lead  plate  becomes 
the  positive  electrode  and  the  lead  peroxide  plate,  the  nega- 
tive electrode,  in  consequence  of  which,  by  the  decomposition 
of  the  sulphuric  acid,  the  anion  S04  migrates  to  the  positive 
lead  electrode,  and  forms  lead  sulphate,  while  the  hydrogen 
separated  on  the  negative  electrode  reduces  the  lead  peroxide 
to  lead  oxide  or  to  metallic  lead. 

These  processes  take  place  according  to  the  following  equa- 
tions : 

On  the -electrode        Pb        +       S0*  PbSO* 

Lead.     Sulphuric  acid  residue.     Lead  sulphate. 

On  the  +  electrode         Pb°*    +    2H    =    Pb°    +    H^ 

Lead  peroxide.    Hydrogen.    Lead  oxide.    Water. 

This  lead  oxide  formed  on  the  +  electrode  also  forms  lead 
sulphate  with  sulphuric  acid,  and  when  all  the  lead  peroxide 
is  reduced,  the  generation  of  current  ceases,  the  accumulator 
is  exhausted,  and  has  to  be  recharged,  whereby  a  repetition  of 
the  processes  above  described  takes  place.  On  the  spongy 
lead  plate  which  has  now  again  become  the  negative  electrode, 
the  lead  sulphate  formed  is  reduced  by  the  hydrogen  to  spongy 
lead  and  sulphuric  acid : 

PbS04     +     2H  ='Pb  +    H2S04 

Lead  sulphate.     Hydrogen.     Lead.     Sulphuric  acid. 

whilst  on  the  positive  electrode  lead  peroxide  is  formed  accord- 
ing to  the  above-described  transpositions. 

From  these  processes  it  follows  that  by  the  discharge  of  the 
accumulator,  sulphuric  acid  for  the  formation  of  lead  sulphate 
is  fixed  on  the  negative,  as  well  as  on  the  positive,  electrode. 
The  electrolyte  must  therefore  contain  less  free  sulphuric  acid 


SOURCES    OF    CURRENT.  115 

than  at  the  time  of  charging,  during  \vhich  the  lead  sulphate  at 
the  negative  electrode  is  reduced  to  lead,  and  oxidized  to  lead 
peroxide  on  the  positive  electrode,  the  sulphuric  acid  of  the 
sulphate  being  thus  again  present  in  the  electrolyte  in  the  form 
of  free  sulphuric  acid.  The  specific  gravity  of  the  electrolyte 
will  be  the  higher,  the  more  free  sulphuric  acid  is  present,  and 
by  determining  it  by  means  of  a  hydrometer  it  can  be  seen 
when  charging  is  finished,  the  latter  being  the  case  when  no 
further  increase  in  the  specific  gravity  is  noticed.  The  com- 
pletion of  charging  is  further  indicated  by  a  copious  escape  of 
oxygen  on  the  positive  pole  plates,  which  is  due  to  the  sul- 
phuric acid  residue  finding  no  more  material  for  the  formation 
of  lead  sulphate,  therefore  forms  sulphuric  acid,  water  being 
decomposed,  while  oxygen  in  the  form  of  gas  is  liberated. 

Liebenow  assumes  that  in  charging  there  are  formed  by  the 
decomposition  of  the  lead  sulphate,  sulphuric  acid-ions,  lead- 
ions,  and,  by  the  co-operation  of  water,  lead  peroxide-ions  and 
hydrogen-ions,  according  to  the  following  equation  : 

2PbS04  +  2H20  =  Pb  +  4H  +  Pb02  +  2S04. 

The  anions  sulphuric  acid  and  lead  peroxide  migrate  to  the 
positive  pole  and  the  cations  lead  -and  hydrogen  to  the  nega- 
tive pole.  However,  on  both  the  poles  only  those  ions  are 
separated  for  the  precipitation  of  which  the  least  work  is 
required,  or,  in  other  words,  whose  decomposition-point  is 
lowest,  which  in  this  case  are  lead  peroxide  and  lead.  Since, 
however,  on  account  of  the  slight  solubility  and  dissociation 
of  lead  salts,  the  ions  in  the  immediate  proximity  of  the  elec- 
trodes would  soon  be  exhausted,  further  charging  can  only 
take  place  when  from  the  lead  sulphate  formed  on  the  elec- 
trodes, fresh  molecules  are  brought  into  solution,  by  the  dis- 
sociation of  which  the  precipitated  ions  are  replaced,  and 
charging  is  only  finished  when  all  the  lead  sulphate  is  dis- 
solved and  separated  as  lead  peroxide  and  lead-sponge.  With 
a  further  passage  hydrogen-ions,  which  possess  the  next 


116  ELECTRO  DEPOSITION    OF    METALS. 

highest  decomposition-point,  are  separated.  The  above-de- 
scribed process  which  in  charging  takes  place  by  the  action  of 
the  current,  progresses  in  a  reverse  sense  when,  by  connecting 
the  positive  and  negative  electrodes,  the  discharge  is  rendered 
possible,  whereby  the  accumulator-current  becomes  available 
ffor  exterior  work.  The  lead  peroxide  is  reduced  and  lead  and 
lead  sulphate  are  formed,  while  on  the  negative  electrode  the 
lead-sponge  is  oxidized,  sulphate  of  lead  being  also  formed  at 
the  same  time. 

According  to  Liebenow's  theory  the  electrolytic  process  is 
reversible  without  loss  of  energy,  while,  according  to  Elbs's, 
the  process  is  irreversible  and  connected  with  a  loss  of  energy. 
In  most  recent  times,  Dolezalek,  Nernst,  Loeb,  and  others, 
have  expressed  themselves  in  favor  of  Liebenow's  view,  while 
Le  Blanc  has  discussed  the  possibility  of  the  formation  of  lead 
peroxide-ions  alongside  of  quadrivalent  lead-ions.  He  as- 
sumes that  at  the  moment  of  discharge,  the  latter  are  con- 
verted into  bivalent  lead-ions,  the  dissolving  lead  peroxide 
furnishing  additional  quadrivalent  lead-ions,  while  at  the 
moment  of  charging  the  bivalent  lead-ions  are  converted  into 
quadrivalent  ones,  and  form  lead  peroxide.  The  view,  that 
instead  of  one  process  in  the  accumulator,  several  processes 
are  jointly  enacted,  may  prove  to  be  the  correct  one. 

Fig.  37  shows  a  common  form  of  an  accumulator.  The 
separate  electrodes  are  insulated  from  each  other  by  glass 
tubes,  the  entire  system  being  secured  by  lead  .springs  which 
press  the  electrodes  against  the  glass  tubes.  Small  accumu- 
lator cells  are  of  glass,  hard  rubber  or  celluloid,  and  larger 
ones  of  wood  lined  with  lead. 

The  sulphuric  acid  used  for  filling  should  be  free  from 
chlorine  and  metallic  impurities,  and  haVe  a  specific  gravity 
of  1.18.  In  a  charged  state  of  the  accumulator,  the  specific 
gravity  rises  to  about  1.21. 

Maintenance  of  accumulators.  An  accumulator  should  never 
be  allowed  to  stand  without  being  charged,  since,  in  such  a 
<;ase,  crystals  of  lead  sulphate  are  formed  upon  the  electrodes, 


SOURCES    OF    CURRENT.  117 

which  can  only  be  removed  with  difficulty,  and  by  this  for- 
mation of  crystals  the  accumulator  acquires  a  very  great  re- 
sistance. When  not  in  use  an  accumulator  should  be  freshly 
charged  every  two  weeks,  because  it  gradually  discharges  itself. 
The  acid  should  be  put  in  the  cells  to  such  a  height  that 
the  electrodes  are  covered  about  5  millimeters  deep  and,  since- 
by  the  evaporation  of  water  and,  especially  by  the  so-called 
"boiling"  of  the  accumulator,  i.  e.,  by  the  escaping  gases  of 
oxygen  and  hydrogen,  sulphuric  acid  is  carried  along,  the 
fluid  has  to  be  brought  to  its  original  level  by  the  addition  of 
dilute  sulphuric  acid  of  1.05  specific  gravity. 

FIG.  37. 


By  the  formation  of  lead  peroxide  and  its  subsequent  reduc- 
tion, the  positive  electrodes  readily  undergo  changes  in  vol- 
ume, they  being  liable  to  buckling  and  the  scaling  off  of 
active  mass  ;  lead-crystals  of  considerable  length  may  deposit 
on  the  negative  electrodes,  both  these  occurrences  giving  rise 
to  short-circuiting.  Hence,  the  accumulator  should  be  fre- 
quently inspected,  and  the  mass  collecting  on  the  bottom,  as 
well  as  the  lead-crystals,  be  removed. 

Charging  of  a  cell  should  always  be  effected  with  a  higher 


118  ELECTRO-DEPOSITION    OF    METALS. 

voltage  than  that  of  the  cell,  and  the  dynamo  should  only  be 
coupled  with  the  accumulator  when  it  furnishes  a  current  of 
sufficiently  good  electro- motive  force.  For  a  single  cell, 
charging  is  commenced  with  an  electro-motive  force  of  2  volts. 
Towards  the  completion  of  charging,  the  electro-motive  force 
of  the  charging  current  should  be  2.6  to  2.7  volts.  After 
interrupting  the  charging  current  the  electro-motive  force  of 
each  cell  falls  off  to  about  2.25  volts. 

During  the  discharge,  the  electro-motive  force  of  the  cells 
rapidly  falls  to  about  2  volts  each,  remaining  constant  at  this 
value  for  quite  a  long  time,  when  it  falls  slowly  to  1.8  volts, 
and  rapidly  from  that  point  on.  The  appearance  of  the  last- 
mentioned  occurrence  should  by  all  means  be  avoided  and, 
when  the  electro-motive  force  falls  to  1.8  volts,  discharge  of 
current  should  be  discontinued,  as  otherwise  the  electrodes 
would  be  subject  to  rapid  destruction. 

Coupling  accumulators.  Like  the  voltaic  cells,  the  individ- 
ual accumulators  may,  according  to  requirement,  be  coupled 
alongside  one  another  (in  parallel),  or  one  after  the  other  (in 
series). 

For  the  production  of  electrolytic  depositions,  cells  of  great 
capacity  have  to  be  taken  exclusively  into  account,  that  is, 
cells  capable  of  yielding  a  great  strength  of  current  for  a  cer- 
tain number  of  hours.  This  value,  current-strength  X  time, 
is  called  ampere-hours  capacity. 

If  for  an  electrolytic  process  a  maximum  electro-motive 
force  of  1.8  volts  is  required,  one  cell  may  be  coupled  to  the 
bath,  or  if  its  capacity  be  insufficient,  several  such  cells  in 
parallel.  If,  on  the  other  hand,  the  bath  requires  a  greater 
electro-motive  force,  two  or  three  cells  will  have  to  be  coupled 
one  after  the  other,  and  an  excess  of  electro-motive  force  has 
to  be  destroyed  by  a  resistance.  The  cells  may  be  charged 
and  discharged  in  parallel,  or  they  may  be  discharged  in 
series  by  means  of  a  transformer,  and  vice  versa,  they  may  be 
charged  in  series  and  discharged  in  parallel,  further  details  of 
which  will  be  given  in  the  Practical  Part. 


IV. 
PRACTICAL  PART. 


CHAPTER  IV. 

ARRANGEMENT    OF    ELECTRO-PLATING    ESTABLISHMENT    IN 

GENERAL. 

ALTHOUGH  rules  valid  for  all  cases  cannot  be  given,  be- 
cause modifications  will  be  necessary  according  to  the  size  and 
extent  of  the  establishment,  the  nature  of  the  articles  to  be 
electro-plated,  and  the  method  of  the  process  itself,  there  are, 
nevertheless,  certain  main  features  which  must  be  taken  into 
consideration  in  arranging  every  establishment,  be  it  large  or 
small. 

Light  in  plating  rooms.  Only  rooms  with  sufficient  light 
should  be  used,  since  the  eye  of  the  operator  is  severely  taxed 
in  judging  whether  the  articles  have  been  thoroughly  freed 
from  fat,  in  recognizing  the  different  tones  of  color,  etc.  A 
northern  exposure  is  especially  suitable,  since  otherwise  the 
reflection  caused  by  the  rays  of  the  sun  may  exert  a  disturbing 
influence.  For  larger  establishments  the  room  containing  the 
baths  should,  in  addition  to  side-lights,  be  provided  with  a 
sky-light,  which,  according  to  the  location,  is  to  be  protected 
by  curtains  from  the  rays  of  the  sun. 

Ventilation.  Due  consideration  must  be  given  to  the  fre- 
quent renewal  of  the  air  in  the  rooms.  Often  it  cannot  be 
avoided  that  the  operations  of  pickling,  etc.,  must  be  carried 
on  in  the  same  room  in  which  the  baths  are  located.  Espe- 
cially unfavorable  in  this  respect  are  smaller  establishments 
working  with  batteries,  in  which  the  vapors  evolved  from  the 

(119) 


120  ELECTRO-DEPOSITION    OF    METALS. 

latter  are  added  to  the  other  vapors,  and  render  the  atmos- 
phere injurious  to  health.  Hence,  if  possible,  rooms  should 
be  selected  having  windows  on  both  sides,  so  that  by  opening 
them  the  air  can  at  any  time  be  renewed,  or  the  baths  and 
batteries  should  be  placed  in  rooms  provided  with  chimneys. 
By  cutting  Holes  of  sufficient  size  in  the  chimneys  near  the 
ceilings  of  the  rooms,  the  discharge  of  injurious  vapors  will  in 
most  cases  be  satisfactorily  effected. 

To  those  working  with  Bunsen  cells,  it  is  recommended  to 
place  them  in  a  closet  varnished  with  asphalt  or  ebonite  lac- 
quer, and  provided  with  lock  and  key.  The  upper  portion 
of  the  closet  should  communicate  by  means  of  a  tight  wooden 
flue  with  a  chimney  or  the  open  air. 

Heating  the  plating  rooms.  Since  the  baths  work  with 
greater  difficulty,  more  slowly  and  more  irregularly  below  a 
certain  temperature,  provision  for  the  sufficient  heating  of  the 
plating  roomg  must  be  made.  Except  baths  for  hot  gilding, 
platinizing,  etc.,  the  average  temperature  of  the  plating  solu- 
tions should  be  from  64.5°  to  68°  F.,  at  which  they  work  best; 
it  should  never  be  below  59°  F.,  for  reasons  to  be  explained 
later  on.  Hence,  for  large  operating  rooms  such  heating 
arrangements  must  be  made  that  the  temperature  of  the  baths 
cannot  fall  below  the  minimum  even  during  the  night,  other- 
wise provision  for  the  ready  restoration  of  the  normal  temper- 
ature at  the  commencement  of  the  work  in  the  morning  has  to 
be  made.  Rooms  heated  during  the  day  with  waste  steam  from 
the  engine,  generally  so  keep  the  baths  during  th'e  winter — the 
only  season  of  the  year  under  consideration — that  they  show  in 
the  evening  a  temperature  of  64.5°  to  68°  F.,  and  if  the  room 
is  not  too  much  exposed,  the  temperature,  especially  of  large 
baths,  will  only  in  rare  cases  fall  below  59°  F.  For  greater 
security  the  heating  pipes  may  be  placed  in  the  vicinity  of  the 
baths,  but  if  this  should  not  suffice  to  protect  the  baths  from 
cooling  off  too  much,  it  is  advisable  to  locate  in  the  plating 
room  a  steam  conduit  of  small  cross-section  fed  from  the  boiler^ 
and  to  pass  stearn  for  a  few  minutes  through  a  coil  of  a  metal 


ELECTRO-PLATING    ESTABLISHMENTS.  121 

indifferent  to  the  plating  solution  suspended  in  the  bath.  In, 
this  manner  baths  of  1000  quarts,  which  on  account  of  several 
days'  interruption  in  the  operation,  had  cooled  to  36°  F.,  were 
in  10  minutes  heated  to  68°  F. 

It  has  also  been  tried  to  heat  large  baths,  for  instance,  nickel 
baths,  by  electrically  heated  boilers.  The  consumption  of 
current  is,  however,  very  great,  and  the  boilers  of  nickel  sheet 
thus  far  do  not  answer  all  rational  demands,  especially  as  re- 
gards durability. 

For  smaller  baths  it  is  advisable  to  bring  a  small  portion  of 
them  in  a  suitable  vessel  to  the  boiling-point  over  a  gas  flame, 
and  add  it  to  the  cold  bath.  If,  after  mixing,  the  tempera- 
ture is  still  too  low,  repeat  the  operation. 

Renewal  of  water.  Another  important  factor  for  the  rooms 
is  the  convenient  renewal  of  the  waters  required  for  rinsing 
and  cleansing.  Without  water  the  electro-deposition  of  metals 
is  impossible  ;  the  success  of  the  process  depending  in  the  first 
place  on  the  careful  cleansing  of  the  metallic  articles  to  be 
electro-plated,  and  for  that  purpose  water,  nay,  much  water, 
hot  and  cold,  is  required,  as  will  be  seen  in  the  section  treating 
on  the  "  Preparation  of  the  Articles."  Large  establishments 
should,  therefore,  be  provided  with  pipes  for  the  admission 
and  discharge  of  water,  one  conduit  terminating  as  a  rose  over 
the  table  where  the  articles  are  freed  from  grease.  In  smaller 
establishments,  where  the  introduction  of  a  system  of  water- 
pipes  would  be  too  expensive,  provision  must  be  made  for  the 
frequent  renewal  of  the  cleansing  water  in  the  various  vats. 

Floors  of  the  plating  rooms.  In  consequence  of  rinsing,  and 
transporting  the  wet  articles  to  the  baths  much  moisture  col- 
lects upon  the  floors  of  the  plating  rooms.  The  best  material 
for  floors  of  large  rooms  is  asphalt,  it  being,  when  moist,  less 
slippery  than  cement.  A  pavement  of  brick  or  mosaic  laid  in 
cement  is  also  suitable,  but  has  the  disadvantage  of  cooling 
very  much.  The  pavement  of  asphalt  or  cement  should  have 
a  slight  inclination,  a  collecting  basin  being  located  at  the 
lowest  point,  which  also  serves  for  the  reception  of  the  rinsing. 


122  ELECTRO-DEPOSITION    OF    METALS. 

water.  Wood  floors  cannot  be  recommended,  at  least  for  large 
establishments,  since  the  constant  moisture  causes  the  wood 
to  rot.  However,  where  their  use  cannot  be  avoided,  the 
places  where  water  is  most  likely  to  collect  should  be  strewn 
with  sand  or  sawdust,  frequently  renewed,  or  the  articles 
when  taken  from  the  rinsing  water  or  bath  be  conveyed  to  the 
next  operation  in  small  wooden  buckets  or  other  suitable 
vessels. 

Size  of  plating  room.  The  plating  room  should  be  of  such  a 
size  as  to  permit  the  convenient  execution  of  the  necessary 
manipulations.  Of  course,  no  general  rule  can  be  laid  down 
in  this  respect,  as  the  size  of  the  room  required  depends  on 
the  number  of  the  processes  to  be  executed  in  it,  the  size  and 
number  of  articles  to  be  electroplated  daily  or  within  a  certain 
time,  etc.  However,  there  must  be  sufficient  room  for  the 
batteries  or  dynamo,  for  the  various  baths,  between  which 
there  should  be  a  passageway  at  least  twenty  inches  wide,  for 
the  table  where  the  articles  are  freed  from  grease,  for  the  lye 
kettle,  hot-water  reservoir,  sawdust  receptacle,  tables  for  tying 
the  articles  to  hooks,  etc. 

Grinding  and  polishing  rooms.  The  rooms  used  for  grinding, 
polishing,  etc.,  also  require  a  good  light  in  order  to  enable  the 
grinder  to  see  whether  the  article  is  ground  perfectly  clean, 
and  all  the  scratches  from  the  first  grinding  are  removed. 
Where  iron  or  other  hard  metals  are  ground  with  emery  it  is 
advisable  to  do  the  polishing  in  a  room  separated  from  the 
grinding  shop  by  a  close  board  partition  ;  because  in  the  pre- 
paratory grinding  with  emery,  which  is  done  dry,  without  the 
use  of  oil  or  tallow,  the  air  is  impregnated  with  fine  particles  of 
emery,  which  settle  upon  the  polishing  wheels  and  materials, 
and  in  polishing  soft  metals  cause  fine  scratches  and  fissures 
which  spoil  the  appearance  of  the  articles,  and  can  be  removed 
only  with  difficulty  by  polishing.  Hence,  all  operations  requir- 
ing the  use  of  emery,  or  coarse  grinding  powders,  should  be 
performed  in  the  actual  grinding  room,  as  well  as  the  grinding 
upon  stones  and  scratch-brushing  by  means  of  rapidly  revolv- 


ELECTRO-PLATING    ESTABLISHMENTS.  123 

ing  steel  scratch-brushes.  Articles  already  plated  are,  of 
course,  scratch-brushed  in  the  plating  room  itself,  either  on  the 
table  used  for  freeing  the  articles  from  grease,  or  on  a  bench 
especially  provided  for  the  purpose.  In  the  polishing  room 
are  only  placed  the  actual  polishing  machines,  which  by  means 
of  rapidly  revolving  wheels  of  felt,  flannel,  etc.,  and  the  use  of 
polishing  powders,  or  polishing  compositions,  impart  to  the 
articles  the  final  luster  before  and  after  electro-plating.  The 
formation  of  dust  in  the  polishing  rooms  is  generally  overesti- 
mated ;  it  is,  however,  sufficiently  serious  to  render  necessary 
the  separation  by  a  close  partition  of  the  polishing  rooms  from 
the  electro-plating  room,  otherwise  the  polishing  dust  might 
settle  upon  the  baths  and  give  rise  to  various  disturbing  phe- 
nomena. In  rooms  in  which  large  surfaces  are  polished  with 
Vienna  lime,  as,  for  instance,  nickeled  sheets,  the  dust  often 
seriously  affects  the  health  of  the  polishers,  especially  in  badly 
ventilated  rooms,  and  in  such  cases  it  is  advisable  to  provide 
a  suitable  apparatus  for  keeping  the  dust  out  of  the  room.  If 
this  cannot  be  done,  wooden  frames  covered  with  packing- 
cloth,  placed  opposite  the  polishing  lathes,  render  good  ser- 
vice; the  packing-cloth  by  being  frequently  moistened  with 
water  retains  a  large  portion  of  the  dust. 

Many  of  the  states  now  have  laws  compelling  firms  to  install 
some  kind  of  apparatus  to  keep  the  dust  out  of  the  room. 
There  are  many  schemes  of  installing  these  exhaust  fans,  the 
most  common  of  which  is,  according  to  T.  C.  Eichstaedt,*  as 
follows:  A  fan  or  blower  of  sufficient  capacity  for  the  number 
of  lathes  in  use  is  generally  placed  at  one  end  of  the  room, 
driven  by  a  belt  or  directly  connected  with  a  motor.  The 
latter  is  the  most  economical  and  the  better  of  the  two.  Then 
the  polishing  and  buffing  lathes  are  placed  in  a  straight  line 
and  a  large  galvanized  iron  pipe,  having  openings  with  intake 
pipes  and  hoods  for  each  wheel,  is  run  to  the  floor  behind  each 
lathe. 

*  Metal  Industry,  March,  1913. 


124  ELECTRO-DEPOSITION    OF    METALS. 

Distance  between  machines.  Care  should  be  taken  to  have 
sufficient  room  between  the  separate  machines  to  prevent  the 
grinders  and  polishers,  when  manipulating  larger  pieces  of 
metal,  from  inconveniencing  each  other.  Tables  for  putting 
down  the  articles  should  also  be  provided. 

Transmission.  For  grinding  lathes  requiring  the  belt  to  be 
thrown  off  in  order  to  change  the  grinding,  it  is  best  to  place 
the  transmission  carrying  the  belt  pulleys  at  a  distance  of 
about  three  feet  from  the  floor,  while  for  lathes  with  spindles 
outside  the  bearings  the  transmission  may  be  on  the  ceiling  or 
wall.  The  revolving  direction  of  the  principal  transmission 
should  be  such  as  to  render  the  crossing  of  the  belts  to  the 
grinding  and  polishing  machines  unnecessary,  otherwise  the 
belts  on  account  of  the  great  speed  will  rapidly  wear  out. 

The  more  modern  electrically-driven  grinding  and  polish- 
ing machines  are  briefly  called  grinding  and  polishing  motors,. 
and  have  decided  advantages  over  machines  driven  by  belts. 
They  will  be  referred  to  later  on  in  the  section  "  Mechanical 
Treatment." 

Electro-plating  Arrangements  in  Particular. 

The  actual  electro-plating  plant  consists  of  the  following 
parts :  1.  The  sources  of  current  (batteries  or  dynamo-electric 
machines)  with  auxiliary  apparatus.  2.  The  current-conductors.. 

3.  The  baths,  consisting  of  the  vats,  the  plating  solutions,  the 
anodes,  and  the  conducting  rods  with  their  binding-screws. 

4.  The  apparatus  for  cleansing,  rinsing,  and  drying. 

Before  entering  into  the  discussion  of  these  separate  parts  of 
an  electro-plating  plant,  it  will  first  be  necessary  to  speak  of 
the  electric  conditions  in  the  electrolyte,  since  what  will  here 
be  said  applies  to  all  electro-plating  processes,  and  will  serve 
for  a  better  comprehension  of  the  succeeding  sections. 

Current- density.  For  the  result  of  the  electrolytic  process, 
the  requisite  to  be  taken  first  of  all  into  consideration  is,  that  a 
sufficient  quantity  of  current  acts  upon  the  surfaces  of  the  ob- 
jects to  be  electro-plated,  and  next  that  the  current  possesses 


ELECTRO-PLATING    ESTABLISHMENTS.  125 

sufficent  electro-motive  force  for  the  decomposition  of  the 
bath.  The  quantity  of  current  which  is  necessary  for  the  nor- 
mal formation  of  an  electro-deposit  upon  1  square  decimeter 
=  10  x  10  centimeters  (100  square  centimeters)  is  now  desig- 
nated as  the  current-density.  In  the  electro-plating  processes 
to  be  described  later  on,  the  suitable  current-density  is  always 
given.  If,  for  instance,  this  normal  current-density  is  for  a 
nickel  bath,  0.4  ampere  per  square  decimeter,  the  electro- 
motive t  force  2.5  volts,  and  the  largest  object-surface  to  be 
nickeled  in  the  bath,  50  cm.  x  20  cm.  =  1000  square  centi- 
meters, a  current  strength  of  at  least  0.4  x  10  =  4  amperes  is 
required.  A  Bunsen  cell,  which  furnishes  4  amperes,  would 
therefore  suffice  if  the  electro-motive  force  required  for  the  de- 
composition of  the  electrolyte  did  not  amount  to  2.5  volts. 
As  previously  mentioned,  a  Bunsen  cell  furnishes  about  1.8 
volts,  and  to  attain  the  greater  electro-motive  force  two  cells 
have  to  be  coupled  one  after  the  other.  The  performance  of 
the  battery  would  then  amount  to  4  amperes  and  3.6  volts, 
and  the  excess  of  electro-motive  force,  which  would  be  an  im- 
pediment to  deposition  proceeding  in  a  normal  manner,  has 
to  be  destroyed  by  a  current-regulator  to  be  described  later  on, 
in  case  it  is  not  preferred  to  increase  the  object-surface  in  the 
bath. 

For  silvering  the  current-density  amounts  to  0.25,  and  a 
silver  bath  with  a  slight  excess  of  potassium  cyanide  requires 
1  volt.  If  now,  for  instance,  an  object-surface  of  55  square 
decimeters,  about  equal  to  50  large  soup  spoons,  is  to  be 
silvered,  55  x  0.25  =  13.75  amperes  and  1  volt  are  required. 
Hence  three  cells  of  5  amperes  each  have  to  be  coupled  along- 
side each  other  to  obtain  15-amperes  current-quantity. 

The  abbreviation  of  ND  100  is  used  to  designate  the  normal 
current-density.  By  multiplying  it  with  the  number  of  square 
decimeters  which  the  object-surface  represents,  the  current- 
strength  required  for  the  object -surface  is  found. 

When  the  current-density  with  which  deposition  is  made  is 
known,  the  quantity  by  weight  of  the  deposit  effected  in  a 


126  ELECTRO-DEPOSITION    OF    METALS. 

definite  time  can  be  readily  calculated.  The  electro-chemical 
equivalent  has  been  referred  to  on  p.  60,  and  it  has  been 
established  that  it  represents  the  number  of  coulombs  which 
separates  1  gramme-equivalent  of  metal  per  second.  When 
by  1  coulomb,  i.  <?.,  by  1  ampere,  0.3290  mg.  copper  per  second 
is  separated  from  cupric  oxide  salts,  1.184  gr.  copper  are 
separated  in  the  ampere-hour  (3600  seconds). 

For  practical  purposes  the  quantities  of  a  metal  separated 
in  1  ampere-hour  are  designated  as  the  electro-chemical  equiv- 
alent of  the  am  pe"  re-hour,  and  the  quantities  of  metal  separated 
with  a  known  current-strength  in  a  definite  time  are  obtained 
by  multiplying  the  electro-chemical  equivalent  with  the  cur- 
rent-strength in  amperes  and  the  number  of  hours. 

For  calculating  the  time  in  which  with  a  known  current- 
strength,  a  certain  quantity  by  weight  is  obtained,  the  latter  is 
simply  divided  by  the  weight  of  the  ampere-hours  deposit  X 
the  current-strength. 

Another  problem  may  be  to  calculate  the  current-strength 
which  is  required  for  furnishing  in  a  certain  time  a  definite 
quantity  by  weight  of  deposit.  For  this  purpose,  divide  the 
quantity  by  weight  by  the  product  of  ampere-hours  deposit 
and  number  of  hours. 

We  will  first  of  all  illustrate  these  calculations  by  two  ex- 
amples without  regard  to  the  current-output.  Suppose  the 
time  is  to  be  determined  during  which  a  square  decimeter  of 
surface  has  to  remain  in  the  nickel  bath  in  order  to  acquire  a 
deposit  of  iV  millimeter  thickness  with  a  current-density  of 
0.4  ampere.  First  calculate  the  weight  of  the  deposit  by  mul- 
tiplying the  surface  in  square  millimeters  with  the  thickness 
and  specific  gravity.  One  square  decimeter  is  equal  to  10,000 
square  millimeters,  which,  multiplied  by  TV  millimeter,  gives 
as  a  product  1000,  which  multiplied  by  the  specific  gravity 
of  nickel — 8.6 — gives  8600  milligrammes  =  8.6  grammes. 
Hence  a  deposit  of  TV  milligramme  thickness  upon  a  surface 
of  1  square  decimeter  represents  a  weight  of  8.6  grammes. 
Since,  for  the  normal  deposit  per  square  decimeter,  a  current- 


ELECTRO-PLATING    ESTABLISHMENTS.  127 

density  of  0.4  ampere  is  required,  and  1  ampere  deposits,  ac- 
cording to  the  table  given  on  p.  61, 1 .1094  grammes  in  1  hour, 
J  ampere  deposits.  0.4437  gramme  in  1  hour,  and,  therefore, 
about  19}  hours  will  be  required  for  the  deposition  of  8.6 
grammes. 

For  calculating  the  time  which  one,  two  or  more  dozen  of 
knives  and  forks  or  spoons,  which  are  to  have  a  deposit  of 
silver  of  a  determined  weight,  must  remain  in  the  bath  when 
the  current-density  is  known,  proceed  as  follows :  Suppose  50 
grammes  of  silver  are  to  be  deposited  upon  1  dozen  of  spoons, 
and  the  most  suitable  current-density  is  0.2  ampere  per  square 
decimeter ;  if  the  surface  of  1  spoon  represents  1.10  square 
decimeters,  the  surface  of  1  dozen  spoons  of  equal  size  is  13.2 
square  decimeters.  Hence,  they  require  13.2  X  0.2  =  2.64 
amperes ;  now,  since  1  ampere  deposits  in  1  hour  4.025 
grammes  of  silver,  2.64  amperes  deposit  in  the  same  time 
10.62  grammes  of  silver,  and  with  this  current,  the  dozen 
spoons  must  remain  about  4}  hours  in  the  bath  for  the  deposi- 
tion of  50  grammes  of  silver  upon  this  surface. 

However,  the  figures  obtained  are  correct  or  approximately 
correct  only  when  the  current-output  amounts  to  100  per 
cent.,  or  to  approximately  this  value,  as  in  the  case  with  acid 
copper  baths,  silver,  gold,  zinc  and  tin  baths ;  with  a  smaller 
current-output  as  yielded  by  potassium  cyanide  copper  and 
brass  baths,  and  nickel  baths,  a  suitable  correction  has  to  be 
made. 

The  current-output  of  a  bath  is  best  determined  as  follows  : 
Deposit  upon  an  accurately  weighed  plate  (sheet)  of  metal  for 
several  hours  with  the  normal  current-density,  and  note  the 
exact  time  of  deposition  and  the  quantity  of  current  measured 
by  a  voltmeter  inserted  in  the  circuit.  Rinse  the  plate  first 
with  water  and  then  with  alcohol  and  ether,  and  dry  thor- 
oughly. Weigh  it  and  by  deducting  the  previous  weight,  the 
weight  of  the  deposit  is  found.  Now  calculate  from  the  table 
of  electro-chemical  equivalents  (p.  61)  how  much  metal  should 
have  been  precipitated  in  the  time  consumed  by  the  current- 


128  ELECTRO-DEPOSITION    OF    METALS. 

strength  used  ;  the  result  will  be  the  theoretical  current-output. 
The  practical  current-output  in  per  cent,  is  found  by  multi- 
plying the  weight  of  the  deposit  found  by  100  and  dividing 
by  the  calculated  weight  of  the  theoretical  current-output. 

Suppose  the  plate  weighs  12.00  grammes  and  after  having 
deposited  upon  it  nickel  for  3  hours  with  1.5  ampere,  it 
weighs  16.45  grammes,  which  corresponds  to  a  deposit  of 
nickel  of  16.45  —  12.00  =  4.45  grammes.  Theoretically, 
1.5  ampere  should  separate  in  3  hours  (1.1094  X  1.5  X  3) 
4.923  grammes  of  nickel.  Hence,  the  practical  current-output 
attained  is 

4.925  :  4.45  =  100  :  x 
x  =  90.35  per  cent. 

In  calculating  the  quantity  by  weight,  the  product  obtained 
from  electro-chemical  equivalent  X  current-strength  X  num- 
ber of  hours,  would  have  to  be  multiplied  by  the  fraction 

Ourrent-output  in  per  cent.    .         ,     n   ,.        ,,       ,.          ,, 

— £ *_        _  ;  m  calculating  tne  time,   the  re- 
sult obtained  above  would  have  to  be  multiplied  by  the  fraction 

,  and   for  calculating  the  current- 
current-output  in  per  cent. 

strength  the  quotient  is  likewise  to  be  multiplied  by  the  frac- 

100 

tion 

current-output  in  per  cent. 

Electro-motive  force  in  the  bath.  It  has  previously  been  seen 
that  for  the  permanent  decomposition  of  an  electrolyte,  an 
electromotive  force  is  required  which  must  be  large  enough 
to  overcome  the  resistance  of  the  electrolyte,  as  well  as  the 
polarization-current  flowing  counter  to  the  main  current. 

The  resistance  of  the  electrolyte  is  found  by  multiplying  its 
specific  resistance,  i.  e.,  the  resistance  of  a  fluid  cube  of  1  deci- 
meter side-length  by  the  electrode  distance  in  decimeters,  and 
dividing  by  the  object-surface  expressed  in  square  decimeters, 
thus, 

Kesistance  of  the  electrolyte  =  Specific  resistance  X  dm.  electrode-distance 

dm.  object-surface. 


ELECTRO-PLATING    ESTABLISHMENTS.  129 

According  to  p.  21,  the  electro-motive  force  required  for 
sending  a  certain  current-strength  through  a  conductor  is 
equal  to  the  product  of  current-strength  and  resistance.  To 
calculate  this  electro-motive  force,  the  resistance  of  the  electro- 
lyte, i.  e.,  of  the  bath,  as  found  above,  has  to  be  multiplied  by 
the  current-density. 

For  the  better  understanding,  an  example  may  here  be 
given,  the  problem  being  to  copper  in  an  acid  copper-bath  an 
object-surface  of  100  square  decimeters. 

Let  the  specific  resistance  of  the  acid  copper-bath  of  a  given 
•composition  be  0.92  ohm,  the  electrode-distance  1.2  decimeters, 
the  normal  current-density  1.25  amperes.  The  required  cur- 
rent-strength, J,  is  found  by  multiplying  the  normal  density 
by  the  object-surface  in  square  decimeters,  thus, 

J  =  100  X  1.25  =  125  amperes. 

From  what  has  above  been  said,  the  resistance,  W,  of  the 
electrolyte  is  obtained  by  multiplying  the  specific  resistance 
by  the  electrode-distance  in  decimeters,  and  dividing  the 
product  by  the  object-surface  in  square  decimeters  : 

0  92  X  1  2 
W=  -  '-  =  0.01104  ohm. 


From  this  the  electro-motive  force,  E,  required  to  send  the 
current-strength,  J,  through  the  bath  is  calculated  : 

E  =  J  X  W  =  125  X  0.01104  -  1.38  volt. 

However,  this  is  valid  only  for  the  normal  temperature  of 
18°  C.  (64.40°  F.).  If  the  electro-motive  force  has  to  be 
calculated,  which  is  required  at  a  higher  temperature,  for 
sending  the  current-strength  of  125  amperes  through  the  bath, 
we  have  to  fall  back  upon  the  temperature-coefficients  and 
the  formulas  given  for  them  on  p.  26,  whereby,  if  the  tem- 
perature of  the  bath  is  24°  C.  (75.2°  F.),  the  equation  assumes 
the  following  form  : 
9 


130  ELECTRO-DEPOSITION    OF    METALS. 

Specific  resistance  =  0.92  (1  —  0.0113  X  6)  =  0.858  ohm. 

Hence  the  temperature-coefficient  0.0113  has  to  be  multi- 
plied by  the  number  of  degrees  C.,  the  bath  is  warmer  than 
18°  C.,  the  product  subtracted  from  1,  and  the  remainder 
multiplied  by  the  specific  resistance  at  18°  C.,  0.92  ohm.  It 
will  be  seen  that  the  specific  resistance  (Sp.  R.),  which  amounts 
at  18°  C.  to  0.92  ohm,  amounts  at  24°  C.  only  to  0.858  ohm. 
The  resistance,  W,  of  the  electrolyte  at  24°  C.  is  therefore 


=  0.0103  ohm, 


and  the  electro-motive  force,  Ej  which  is  capable  of  forcing 
125  amperes  through  the  resistance  of  0.0103  ohm  : 

E  =  J  X  W  =  125  X  0.0103  =  1.287  volt. 

If  the  electrolyte  is  6°  C.  colder  than  18°  C.,  the  formula  is 
so  changed  that  the  temperature-coefficient  0.0113  has  to  be 
multiplied  by  6,  the  product  added  to  1,  and  the  sum  multi- 
plied by  the  specific  resistance  (Sp.  R.)  : 

Sp.  R.  —  0.92  (1  +  0.0113  X  6)  =  0.9824  ohm  ; 
the  resistance  of  the  bath  is  then  : 


the  electro-motive  force  required  being  therefore  : 

E  =  J  X  W  =  125  X  0.01178  =  1.472  volt. 

Electro-motive  counterforce  of  polarization.  In  addition  to- 
this  resistance  of  the  electrolyte,  the  electro-motive  counter- 
force  of  the  polarization-current  has  to  be  taken  into  consider- 
ation. The  causes  of  polarization  have  been  explained  on  p. 
65  ;  it  being  partly  due  to  the  formation  of  gas-cells  during 


ELECTRO-PLATING    ESTABLISHMENTS.  131 

electrolysis  with  insoluble  electrodes,  especially  anodes,  partly 
to  changes  in  concentration  in  the  vicinity  of  the  electrodes,  or 
to  oxidizing  or  reducing  processes  in  the  electrolyte.  In  most 
cases  of  electrolysis  coming  here  in  question,  the  dilution 
formed  on  the  cathodes  by  the  separation  of  metal  will  send  a 
polarization-current  towards  the  more  concentrated  layers  of 
fluid  formed  by  the  solution  of  the  anode-metal,  to  which  is 
added  the  counter-current  formed  by  the  contiguity  of  fluids 
with  salts  of  a  lower  degree  of  oxidation  to  fluids  with  salts  of 
a  higher  degree  of  oxidation.  The  magnitude  of  polarization 
is  materially  influenced  by  the  nature  of  the  metals  of  which 
the  electrodes  consist ;  the  more  electro-positive  the  cathode- 
metal  and  the  more  electro-negative  the  anode-metal,  the 
greater  the  electro-motive  force  of  the  polarization-current 
which  flows  from  the  more  positive  cathode  to  the  negative 
anode,  hence  in  an  opposite  direction  to  the  main  current, 
which  enters  at  the  anode  and  passes  out  at  the  cathode. 
This  explains  why  in  nickeling  iron  less  electro-motive  force  is 
required  than  in  nickeling  zinc,  iron  being  only  to  a  slight 
degree  more  positive  than  the  nickel-metal  of  the  anode,  and 
hence  less  electro-motive  counterforce  appears.  Zinc,  on  the 
other  hand,  is  far  more  positive  than  iron,  and  the  electro- 
motive force  of  the  polarization-current  is  consequently  essen- 
tially stronger. 

The  determination  of  this  electro-motive  counterforce  is  in 
the  most  simple  manner  effected  by  experiment.  If  a  volt- 
meter of  great  resistance  be  placed  at  the  bath,  and  the  main 
current  which  had  been  passed  into  the  bath  be  suddenly  in- 
terrupted by  means  of  a  switch,  the  needle  of  the  voltmeter 
does  not  at  once  return  to  the  0-point,  but  remains  for  some 
time  in  a  position  above  that  point,  and  then  gradually  re- 
turns to  it.  The  electro-motive  force  indicated  by  the  needle 
for  the  short  time  after  the  interruption  of  the  current  gives 
the  electro-motive  force  of  the  polarization-current. 

The  electro-motive  counterforce  is  influenced  by  the  magni- 
tude of  the  current-density,  growing  and  falling  with  the  latter. 


132  ELECTRO-DEPOSITION   OF    METALS. 

When  the  magnitude  of  the  counterforce  has  been  determined 
by  experiment  as  above  described,  the  electro-motive  force  of 
the  main  current  required  for  the  electrolytic  process  is  made 
up  of  the  electro-motive  force  found  by  multiplying  the  current- 
strength  by  the  resistance  of  the  electrolyte  plus  the  electro- 
motive counterforce  of  polarization  found  by  experiment. 

Proceeding  from  the  opinion  that  the  electric  current-lines 
are  subject  to  scattering  similar  to  the  magnetic  lines  of  force, 
Pfanhauser  has  taken  into  account  the  magnitude  of  this  scatter- 
ing of  the  current-lines  for  the  calculation  of  the  resistance  of 
the  electrolyte.  When  such  scattering  takes  place,  the  current- 
lines  will  not  collectively  migrate  by  the  shortest  road  from  the 
anode  to  the  cathode,  but  describe  greater  or  smaller  curves, 
the  cross-section  of  the  fluid  which  takes  part  in  the  conduc- 
tion of  the  current,  becoming  thereby  greater  than  if  the  cur- 
rent would  pass,  without  deviation  whatever,  between  the  elec- 
trodes, and  the  resistance  of  the  electrolyte  consequently  be- 
comes smaller.  The  least  scattering  was  found  with  electrodes 
of  the  same  size,  it  increasing  with  the  greater  distance  of  the 
electrodes  from  each  other.  In  electro-plating  processes  run- 
ning a  normal  course,  the  decrease  in  the  resistance  of  the 
bath  by  the  scattering  of  current-lines  may  practically  be 
disregarded,  and  it  will  later  on  only  be  referred  to  in  so  far 
as  various  phenomena  which  appear  in  electro-plating  have 
been  explained  by  this  scattering. 

We  will  now  turn  to  the  discussion  of  electro-plating  installa- 
tions with  the  different  sources  of  current,  and  the  arrangement 
with  cells  will  first  be  described.  It  will  be  necessary  to  specify 
in  this  section  all  the  laws  and  rules  which  are  also  valid  for 
installations  with  other  sources  of  current,  and  the  reader  is 
requested  thoroughly  to  study  this  section,  as  repetition  in 
subsequent  sections  is  not  feasible. 

A.     INSTALLATIONS  WITH  CELLS. 

Coupling  of  cells.  Prior  to  the  time  when  it  became  possible 
to  calculate  the  normal  current-strength  for  a  definite  object- 


ELECTRO-PLATING    ESTABLISHMENTS.  133 

surface,  because  the  magnitude  to  which  the  term  current- 
density  has  been  applied  was  not  known,  the  transmission  of  the 
quantity  of  current  required  for  the  electro-plating  processes 
was  effected  in  a  purely  empirical  manner.  The  effective  zinc 
surface  of  the  cells  was  taken  as  the  basis,  and  it  was  held  that 
with  baths  of  medium  resistance  a  good  deposit  is  generally 
effected  when  the  effective  zinc-surface  of  the  cells  is  of  the 
same  size  as  the  object-surface  which  is  to  be  plated,  and  as 
large  as  the  anode-surfaces.  The  electro-motive  force  required 
was  obtained  by  coupling  a  larger  or  smaller  number  of  cells 
one  after  the  other.  Suppose  we  have  a  nickel  bath  which 
requires  for  its  decomposition  a  current  of  2.5  volts  of  electro- 
motive force.  Now  since,  according  to  p.  78,  a  Bunsen  cell 
develops  a  current  of  1.88  volts,  the  reduction  of  the  nickel 
cannot  be  effected  with  one  such  cell  alone,  but  two  cells  will 
have  to  be  coupled  for  electro-motive  force  one  after  the  other, 
whereby,  leaving  the  conducting  resistance  of  the  wires  out  of 
consideration,  an  electro-motive  force  of  2  X  1.88  =  3.76  volts 
is  obtained,  with  which  the  decomposition  of  the  solution  can 
be  effected. 

If,  on  the  other  hand,  we  have  a  silver  bath  which  requires 
only  1  volt  for  its  decomposition,  we  do  not  couple  two  cells 
one  after  the  other,  because  the  electro-motive  force  of  a  single 
cell  suffices  for  the  reduction  of  the  silver.  On  p.  88  it  has 
been  seen  that  by  coupling  the  elements  one  after  the  other 
(coupling  for  electro-motive  force)  the  electro-motive  force  of 
the  battery  is  increased,  but  the  quantity  of  current  is  not  in- 
creased, and  that  to  attain  the  latter,  the  cells  must  be  coupled 
alongside  of  one  another  (coupled  for  quantity).  Hence  in  a 
group  of,  for  instance,  three  cells  coupled  one  after  another, 
only  one  single  zinc  surface  of  the  cells  can  be  considered 
effective  in  regard  to  the  quantity  of  current.  Now,  the  larger 
the  area  of  articles  at  the  same  time  suspended  in  the  bath  is, 
the  greater  the  number  of  such  effective  zinc  surfaces  of  the 
group  of  cells  to  be  brought  into  action  must  be ;  and,  if  for 
baths  with  medium  resistance,  it  may  be  laid  down  as  a  rule 


134 


ELECTRO-DEPOSITION    OF    METALS. 


that  the  effective  zinc  surface  must  be  at  least  as  large  as  the 
surface  of  the  articles,  provided  the  surface  of  the  anodes  is  at 
least  equal  to  the  latter,  the  approximate  number  of  cells  and 
their  coupling  for  a  bath  can  be  readily  found. 

Let  us  take  the  nickel  bath  of  medium  resistance  which,  as 
above  mentioned,  requires  a  current  of  2.5  volts,  and  for  the 
decomposition  of  which  two  cells  must,  therefore,  be  coupled 
one  after  the  other,  and  suppose  that  the  zinc  surface  of  the 
Bunsen  cells  is  500  square  centimeters,  then  the  effective  zinc 
surface  of  the  two  cells  coupled  one  after  the  other  will  also  be 
500  square  centimeters ;  hence  a  brass  sheet  20  X  25  =  500 
centimeters  can  be  conveniently  nickeled  on  one  side  with 

FIG.  38. 


these  two  cells,  or  a  sheet  10  X  25  =  250  centimeters  on  both 
sides.  Now  suppose  the  surface  to  be  nickeled  were  twice  as 
large,  then  the  two  cells  would  not  suffice,  and  a  second  group 
of  two  cells,  coupled  one  after  the  other,  would  have  to  be 
joined  to  the  first  group  for  quantity,  as  shown  in  Fig  19,  or 
perspectively  in  Fig.  38.  Three  times  the  object-surface 
would  require  three  groups  of  elements,  and  so  on. 

In  giving  these  illustrations  it  is  supposed  the  objects  are 
to  have  a  thick,  solid  plating.  For  rapid  plating  and  a  thin 
deposit  a  different  course  has  to  be  followed.  Only  a  slight 
excess  of  electro-motive  force  in  proportion  to  the  resistance  of 
the  bath  being  in  the  above-mentioned  case  present,  reduction 
takes  place  slowly  and  uniformly  without  violent  evolution  of 


ELECTRO-PLATING    ESTABLISHMENTS.  135 

gas  on  the  objects,  and  by  the  process  thus  conducted,  the 
deposit  formed  is  sure  to  be  homogeneous  and  dense,  since  it 
absorbs  but  slight  quantities  of  hydrogen,  and  in  most  cases  it 
can  be  obtained  of  such  thickness  as  to  be  thoroughly  resistant. 

For  rapid  plating,  without  regard  to  great  solidity  and 
thickness  of  the  deposit,  the  cells,  however,  have  to  be  coupled 
so  that  the  electro-motive  force  is  large  as  compared  with  the 
resistance  of  the  bath,  so  that  the  current  can  readily  overcome 
the  resistance.  This  is  accomplished  by  coupling  three,  four, 
or  more  cells  one  after  the  other,  as  shown  in  the  scheme,  Fig. 
18.  However,  special  attention  has  to  be  drawn  to  the  fact 
that  deposits  produced  with  a  large  excess  of  electro-motive 
force  can  neither  be  dense  nor  homogeneous,  because,  in 
accordance  with  the  generally  accepted  view,  the  deposits  con- 
dense and  retain  relatively  large  quantities  of  hydrogen  gas, 
the  term  occlusion  being  applied  to  this  property. 

Current  regulation.  Only  in  very  rare  cases  will  it  be  possi- 
ble to  always  charge  a  bath  or  several  baths  with  the  same 
object-surface ;  and  according  to  the  amount  of  business,  or 
the  preparation  of  the  objects  by  grinding,  polishing  and 
pickling,  at  one  time  large,  and  at  another,  small  surfaces  will 
be  suspended  in  the  bath.  Now,  suppose  a  battery  suitable 
for  a  correct  deposit  upon  a  surface  of,  say  five  square  feet, 
has  been  grouped  together  ;  and,  after  taking  the  articles  from 
the  bath,  a  charge  of  objects  only  half  as  large  as  before  is 
introduced,  the  current  of  the  battery  will,  of  course,  be  too 
strong  for  this  reduced  surface,  and  there  will  be  danger  of 
the  deposit  not  being  homogeneous  and  dense,  but  forming 
with  a  crystalline  structure,  the  consequence  of  which,  in  most 
cases,  will  be  slight  adhesiveness,  if  not  absolute  uselessness. 
With  sufficient  attention  the  total  spoiling  of  the  articles 
might  be  prevented  by  removing  the  objects  more  quickly 
from  the  bath.  But  this  is  groping  in  the  dark,  the  objects 
being  either  taken  too  soon  from  the  bath,  when  not  suffi- 
ciently plated,  or  too  late,  when  the  deposit  already  shows  the 
consequences  of  too  strong  a  current. 


136 


ELECTRO-DEPOSITION    OP    METALS. 


For  the  control  of  the  current  an  instrument  called  a  cur- 
rent-regulator,  resistance  board  or  rheostat  has  been  devised, 
which  allows  of  the  current-strength  of  a  battery  being  re- 
duced without  the  necessity  of  uncoupling  cells.  It  is  obvious 
that  the  current  of  a  battery,  if  too  strong,  can  be  weakened 
by  decreasing  the  number  of  cells  forming  the  battery,  and 
also  by  decreasing  the  surface  of  the  anodes,  because  the  ex- 
ternal  resistance  is  thereby  increased.  This  coupling  and 
uncoupling  of  cells  is,  however,  not  only  a  time-consuming, 
but  also  a  disagreeable,  labor  ;  and  it  is  best  to  use  a  resistance- 


FIG.  39. 


FIG.  40. 


board  with  which,  by  the  turn  of  a  lever,  the  desired  end  is 
attained.     Figs.  39  and  40  show  this  instrument. 

Its  action  is  based  upon  the  following  conditions  :  As  previ- 
ously explained,  the  maximum  performance  of  a  battery  takes 
place  when  the  external  resistance  is  equal  to  the  internal  re- 
sistance of  the  battery.  By  increasing  the  external  resistance, 
the  performance  is  decreased,  and  a  current  of  less  intensity 
will  pass  into  the  bath  when  resistances  are  placed  in  the 
circuit.  The  longer  and  thinner  the  conducting  wire  is,  and 
the  less  conducting  power  it  possesses,  the  greater  will  be  the 
resistance  which  it  opposes  to  the  current.  Hence,  the  resist- 


ELECTRO-PLATING    ESTABLISHMENTS. 


137 


ance  board  consists  of  metallic  spirals  which  lengthen  the 
circuit,  contract  it  by  a  smaller  cross-section,  and  by  the  nature 
of  the  metallic  wire,  has  a  resistance-producing  effect.  For  a 
slight  reduction  of  the  current,  copper  spirals  of  various  cross- 
sections  are  taken,  which  are  succeeded  by  brass  spirals,  and 
finally  by  German-silver  spirals,  whose  resistance  is  eleven 
times  greater  than  that  of  copper  spirals  of  the  same  length 
and  cross-section.  In  Fig.  39  the  conducting  wire  coming 
from  the  battery  goes  to  the  screw  on  the  left  side  of  the  re- 
sistance board,  which  is  connected  by  stout  copper  wire  with 
the  first  contact-button  on  the  left;  hence  by  placing  the 
metallic  lever  upon  the  button  furthest  to  the  left,  the  current. 


FIG.  41. 


BATH 


BATTERY 

passes  the  lever  without  being  reduced,  and  flows  off  through 
the  conducting  wire  secured  to  the  setting-screw  of  the  lever. 
By  placing  the  lever  upon  the  next  contact  button  to  the  right, 
two  copper  spirals  are  brought  into  the  circuit ;  by  turning  the 
lever  to  the  next  button,  four  spirals  are  brought  into  the 
circuit,  and  so  on.  By  a  proper  choice  of  the  cross-sections  of 
the  spirals,  their  length,  and  the  metal  of  which  they  are 
made,  the  current  may  be  more  or  less  reduced  as  desired. 

In  case  great  current-strengths  must  flow  through  the  re- 
sistance board,  it  is  more  advantageous  to  couple  the  spirals- 
in  parallel,  and  not  one  after  the  other,  as  in  Figs.  41  and  42. 


138 


ELECTRO-DEPOSITION    OP    METALS. 


The  resistance  boards  may  be  placed  in  the  circuit  itself  in 
two  different  ways.  If  the  resistance  board  is  to  maintain  the 
electro-motive  force  of  the  current  at  the  bath  constant  at  a 
certain  height,  it  is  coupled  in  series.  In  this  case  the  same 
current-strength  which  is  consumed  at  the  bath  flows  through 
the  resistance.  This  coupling  in  series,  or  one  after  the  other, 
of  the  resistance  board  is  shown  in  Fig.  41. 

In  the  other  mode  of  coupling,  Fig.  42,  the  resistance  lies 
in  shunt  to  the  circuit,  it  being  coupled  parallel  to  it.  Accord- 
ing to  KirchofF's  law,  if  there  be  a  branching-off  of  the 
•current,  the  sum  of  the  current-strengths  in  the  separate 


FIG.  42. 


BATU 


cJliAvitATo^ 


BATTERY 


branches  is  just  as  great  as  the  current-strength  prior  to  and 
after  branching  off,  and  the  current-strengths  in  the  separate 
branches  are  inversely  proportional  to  the  resistances  of  the 
separate  branches. 

In  the  case  in  question  the  coupling  of  the  resistance-board 
{Fig.  42)  represents  such  a  branching-off  of  the  current ;  the 
greater  the  resistance  of  the  resistance-board,  the  less  the 
current-strength  will  be  which  flows  through  it ;  otherwise,  a 
•greater  resistance  in  the  main  circuit,  hence  in  this  case  in  the 
bath,  will  cause  a  portion  of  the  current-strength  to  flow  through 
*the  resistance-board,  where  it  is  destroyed. 


ELECTRO-PLATING    ESTABLISHMENTS.  139 

The  parallel  coupling  of  the  resistance-board  with  the  bath, 
is  utilized  to  remove  differences  in  the  operating  electro- 
motive force  of  baths  coupled  in  series,  which  may  appear 
by  electrode-surfaces  of  uneven  size,  or  by  changes  in  the 
resistances  of  the  electrolytes. 

Current  indicator.  In  order  to  be  able  to  control  the  change 
in  the  current-conditions  which  is  effected  in  a  circuit  by  the 
resistance-board,  a  galvanometer  is  coupled  behind  the  latter. 
This  instrument  consists  of  a  magnetic  needle  oscillating  upon 
a  pin,  below  which  the  current  is  conducted  through  a  strip  of 
copper,  or,  with  weaker  currents,  through  several  coils  of  wire. 
The  electric  current  deflects  the  magnetic  needle  from  its  north- 
pole  position,  and  the  more  so  the  stronger  the  current  is ; 
hence  the  current-strength  of  the  battery  can  be  determined 
by  the  greater  or  smaller  deflection. 

For  a  weak  current,  such  as,  for  instance,  that  yielded  by 
two  cells,  it  is  of  advantage  to  use  a  horizontal  galvanometer 
(Fig.  43).     It  is  screwed  to  a  table  by 
means  of  a  few  brass  screws  in  such  a  FlG-  43- 

position  that  the  needle  in  the  north  posi- 
tion, which  it  occupies,  points  to  0°  when 
no  current  passes  through  the  instru- 
ment. Articles  of  iron  and  steel  must,  of 
course,  be  kept  away  from  the  instrument.  , 

For  stronger  currents  it  is  better  to  combine  a  vertical  galvano- 
meter with  the  switch-board  and  fasten  it  to  the  same  frame, 
as  shown  in  Fig.  44.  The  screw  of  the  lever  of  the  switch- 
board is  connected  with  one  end  of  the  copper  strip  of  the 
vertical  galvanometer,  while  the  other  is  connected  with  the 
screw  on  the  right  side  of  the  switch-board,  in  which  is  se- 
cured the  wire  leading  to  the  bath.  The  switch-board  and 
galvanometer  are  placed  in  one  conducting  wire  only,  either 
in  that  of  the  anodes  or  of  the  objects,  one  of  these  wires 
being  simply  cut,  and  the  end  connected  to  the  battery,  is 
secured  in  the  binding-screw  on  the  side  of  the  resistance 
board  marked  "  strong,"  while  the  other  end,  which  is  in  con- 


140  ELECTRO-DEPOSITION    OF    METALS. 

nection  with  the  bath,  is  secured  in  the  binding-screw  on  the 


FIG.  44. 


opposite  side  marked  "weak."     The  entire  arrangement  will 
be  perfectly  understood  from  Figs.  44  and  45. 


FIG.  45. 


Fig.  46  shows  the  Hanson  &  Van  Winkle  Patent  Under- 


ELECTRO-PLATING    ESTABLISHMENTS.  141 

writer's  Rheostat.  It  has  twice  the  carrying  capacity  of  any 
resistance  board^ever  made  for  this  purpose,  it  having  sufficient 
length  of  wire  to  allow  of  turning  down  the  highest  electro- 
motive force  used  in  plating,  to  the  lowest  figure  called  for, 
without  showing  heat  or  any  unfavorable  symptoms.  By  the 
use  of  this  rheostat  the  output  from  a  plating  room  using  two 
or  more  tanks  can  be  doubled,  providing  the  dynamo  has  the 
current  capacity. 

FIG.  46. 


Fig.  47  shows  a  special  rheostat  constructed  by  the  Hanson 
<fe  Van  Winkle  Co.  for  use  on  nickel,  copper  or  brass  solutions 
requiring  heavy  ampereage.  For  the  reason  that  so  large  an 
ampere  current  is  used  the  instrument  is  especially  constructed 
to  withstand  any  excessive  heating  to  which  it  may  be  sub- 
jected. This  rheostat  may  also  be  used  in  the  main  line  to 
control  the  voltage  of  several  tanks.  It  is  suitable  for  solutions 
containing  175  to  200  square  feet  of  nickel  work,  or  on  copper 
or  brass  baths  of  100  to  125  square  feet,  or  for  zinc  solution 
containing  75  feet  of  work  surface. 

The  advantages  derived  from  the  use  of  a  resistance  board 


142 


ELECTRO-DEPOSITION  OF  METALS. 


having  been  referred  to,  it  remains  to  add  a  few  words  regard- 
ing the  indications  made  by  the  galvanometer.  Since  the 
greater  deflection  of  the  needle  depends,  on  the  one  hand,  on 
the  greater  current-strength,  and  on  the  other,  on  the  slighter 
resistance  of  the  exterior  closed  circuit  (conducting-wires, 
baths  and  anodes),  it  is  evident  that  a  bath  with  slighter  re- 
sistance, when  worked  with  the  same  battery  and  containing 

FIG.  47. 


•Hr 


the  same  surface  of  anodes  and  objects,  will  cause  the  needle 
to  deflect  more  than  a  bath  of  greater  resistance  under  other- 
wise equal  conditions. 

Hence,  the  deductions  drawn  from  the  position  of  the  needle 
for  the  electro-plating  process  are  valid  only  for  definite  baths 
and  definite  equal  conditions,  but,  with  due  consideration  of 
these  conditions,  are  of  great  value. 

Suppose  a  nickel  bath  to  work  always  with  the  same  surfaces 


ELECTRO-PLATING    ESTABLISHMENTS.  143- 

of  objects  and  anodes,  and  experiments  have  shown  that  the 
suitable  current-strength  for  this  surface  of  objects  is  that  at 
which  the  needle  stands  at  15°  ;  and  suppose,  further,  that  the 
battery  has  been  freshly  filled  and  causes  the  needle  to  deflect 
to  25°,  then  the  lever  of  the  resistance  board  will  have  to  be 
turned  so  far  to  the  right  that  the  needle  in  consequence  of  the 
interposed  resistances  returns  to  15°.  Now  if,  after  working 
for  some  time,  the  battery  yields  a  weaker  current,  the  needle, 
by  reason  of  the  resistance  remaining  the  same,  will  constantly 
retrograde,  and  has  to  be  brought  back  to  15°  by  turning  the 
lever  to  the  left,  when  a  current  of  equal  strength  to  the  former 
will  again  flow  into  the  bath.  This  manipulation  is  repeated 
until  finally  the  lever  rests  upon  the  button  furthest  to  the  left, 
at  which  position  the  current  flows  directly  into  the  bath  with- 
out being  influenced  by  the  resistances  of  the  resistance  board. 
If  now  the  needle  retrogrades  below  15°,  it  is  an  indication  to 
the  operator  that  he  must  renew  the  filling  of  the  battery  if  he 
does  not  prefer  suspending  fewer  objects  in  the  bath.  For  this 
reduced  object-surface  it  is  no  longer  required  for  the  needle 
to  stand  at  15°  in  order  to  warrant  a  correct  progress  of  the 
electric  process,  since  the  resistance  being  in  this  case  greater, 
a  deflection  to  10°,  or  still  less,  may  suffice.  This  example 
will  make  it  sufficiently  clear  that  the  current-indication  by 
the  galvanometer  is  not  and  cannot  be  absolute,  but  that  the 
deductions  must  always  be  drawn  with  due  consideration  ta 
the  conditions,  namely,  surfaces  of  objects  and  anodes,  and 
distance  between  them. 

It  frequently  happens  that  in  consequence  of  defective  con- 
tacts with  the  binding-screws  of  the  battery,  or  by  the  con- 
ductors of  the  objects  and  of  the  anodes  touching  one  another 
(short  circuit  with  non-insulated  conducting  wires),  no  current 
whatever  flows  into  the  bath.  Such  an  occurrence  is  immedi- 
ately indicated  by  the  galvanometer,  the  needle  being  not  at 
all  deflected  in  the  first  case,  while  in  the  latter  the  deflection 
will  be  much  greater  than  the  usual  one. 

The  needle  of  the  galvanometer  also  furnishes  a  means  of 


144  ELECTRO-DEPOSITION    OF    METALS. 

recognizing  the  polarity  of  the  current.  If  the  galvanometer 
be  placed  in  the  positive  (anode)  conductor  by  securing  the 
wire  coming  from  the  battery  in  the  binding-screw  on  the 
south  pole  of  the  galvanometer,  and  the  wire  leading  to  the 
bath  in  the  binding-screw  on  the  north  pole  of  the  needle,  the 
needle,  according  to  Ampere's  law,  will  be  deflected  in  the 
direction  of  the  hands  of  a  watch,  i.  e.,  to  the  right  if  the  ob- 
server stands  so  in  front  of  the  galvanometer  as  to  look  from 
the  south  pole  towards  the  north  pole,  because  the  battery- 
current  flows  out  from  the  positive  pole  through  the  conduct- 
ing wire,  anodes,  and  fluid  to  the  objects,  and  from  these  back 
through  the  object  wire  to  the  negative  pole  of  the  battery.  If 
now  in  consequence  of  the  counter-current  formed  in  the  bath 
by  the  metallic  surfaces  of  dissimilar  nature  or  other  causes,  and 
flowing  in  an  opposite  direction  to  that  of  the  battery-current, 
the  latter  is  weakened,  the  needle  will  constantly  further  retro- 
grade from  the  zero  point,  and  when  the  counter-  or  polariza- 
tion-current becomes  stronger  than  the  battery-current,  it  will 
be  deflected  in  an  opposite  direction  as  before.  Hence,  by 
observing  the  galvanometer,  the  operator  can  avoid  the  annoy- 
ing consequences  of  polarization,  which  will  be  further  dis- 
cussed under  nickeling. 

Measuring  instruments.  It  may  here  be  stated  that  the  use 
of  the  galvanometer  has  been  to  a  great  extent  abandoned, 
and  measuring  instruments  are  at  present  generally  employed. 

For  measuring  the  current-strength,  the  ampere-meter  or 
ammeter  is  employed,  and  for  measuring  the  electro-motive 
force  of  the  current,  the  volt-meter,  these  instruments  allowing 
of  the  direct  reading  off  of  the  current-strength  in  amperes 
and  of  the  electro-motive  force  in  volts. 

Space  will  not  permit  us  to  enter  into  the  different  construc- 
tions of  these  measuring  instruments,  and  only  the  principle 
of  their  construction  will  here  in  a  few  words  be  explained. 

It  has  previously  been  seen  that  with  a  given  object-  and 
anode-surface,  the  deposit  in  the  plating  bath  depends  chiefly 
on  the  current-strength  and  electro-motive  force  of  the  cur- 


ELECTRO-PLATING    ESTABLISHMENTS.  145 

rent.  The  deposit  will  turn  out  most  beautiful  and  most 
homogeneous  only  with  a  definite  current-strength,  and  though 
the  skilled  operator  may  succeed  by  empirical  experiments  in 
obtaining  a  beautiful  deposit  without  a  knowledge  of  the  cur- 
rent-conditions, this  mode  of  working  requires  far  more  atten- 
tion than  when  by  simply  reading  off  the  deflection  of  the 
needle  on  the  measuring  instruments,  it  can  be  ascertained 
that  the  bath  works  in  the  most  rational  manner,  without 
having  first  to  inspect  the  objects  and  the  bath  itself.  Such 
instruments  are  a  great  convenience,  especially  with  a  varying 
size  of  the  object-surface,  particularly  if  each  bath  is  provided 
with  one,  because  the  electro-motive  force  at  the  bath  changes 
every  time  the  object-surface  is  changed.  Hence,  as  pre- 
viously stated,  the  current  has  every  time  to  be  regulated 
before  it  is  allowed  to  pass  into  the  bath,  if  the  deposit  is  to 
be  always  of  the  same  quality. 

While  voltmeters  allow  of  a  reliable  control  of  the  electro- 
motive force  in  the  bath,  ammeters  serve  the  purpose  of  recog- 
nizing, on  the  one  hand,  whether  the  current-strength  required 
for  a  certain  object-surface  passes  into  the  bath,  if  the  calcu- 
lation of  the  total  current-strength  is  based  upon  the  normal 
current-density.  %0n  the  other  hand,  they  allow  of  the  deter- 
mination of  the  quantities  by  weight  of  metal  deposited,  the 
weight  of  the  deposit  depending  solely  on  the  current-strength. 
Although  it  is  not  always  necessary  to  know  this,  yet  it  is 
frequently  desirable  to  ascertain  how  great  the  current- 
strength  is,  in  order  to  determine  what  demands  are  made  on 
the  battery  or  the  dynamo. 

Notwithstanding  their  extraordinary  simplicity,  the  instru- 
ments constructed  according  to  Hummel's  patent,  are  very 
sensitive,  and  do  not  change  in  the  course  of  time  as  is  the 
case  with  many  other  constructions.  Their  mode  of  action  is 
based  upon  the  phenomenon  that  soft  iron  is  attracted  by  a 
current-conductor.  In  the  scheme,  Fig.  48,  S  is  a  circular 
current-conductor,  consisting  of  a  greater  or  smaller  number 
of  copper-wire  coils.  In  the  interior  is  a  piece  of  thin  sheet- 
10 


146 


ELECTRO-DEPOSITION    OF    METALS. 


FIG.  48. 


iron,    E,-  connected  with  an   axis  of  revolution,  a.     G  is  a 

weight  which  is  to  be  lifted  by  the  attractive  force  of  the  cur- 
rent S  upon  the  iron  E.  The 
stronger  the  current,  the  greater 
the  attraction  of  the  coils  lying 
next  to  the  sheet-iron,  and,  hence, 
the  greater  the  elevation  of  the 
weight,  G,  will  be,  and  the  further 
the  indicator,  Z,  connected  with 
the  axis  of  revolution,  and  below 
which  a  scale  is  fixed,  will  deflect. 
As  regards  construction,  the 
^  voltmeter  and  ammeter  are  alike 

with  the  exception  of  the  coil  S. 
In   the   voltmeter   it    consists   of 

^^^  v^^  many    windings    of  thin    copper 

^fe=r±==^£^  wire,  and  in  the  ammeter  of  but 

a   few  windings  of  stout   copper 

wire,  or  in  instruments  for  great  current-strength,  of  a  massive 

bent  piece  of  copper. 

Fig.  49  shows  the  "Waverly"  voltmeter,  manufactured  by 

FIG.  49. 


the  Hanson  and  Van  Winkle  Co.,  Newark,  N.  J.  It  is  in- 
tended for  direct  current  circuits  only;  0  to  10  volts.  It  is 
furnished  with  binding  posts  for  fourteen  tanks,  thus  enabling 


ELECTRO-PLATING    ESTABLISHMENTS. 


147 


the  operator  to  use  only  one  instrument  in  obtaining  the  read- 
ing of  any  number  of  tanks  up  to  fourteen,  by  simply  moving 
the  switch  lever  to  the  tank  numbers  indicated  on  the  switch 
•of  the  instrument,  and  when  used  in  connection  with  the 
patent  tank  rheostat,  will  enable  the  operator  to  reproduce  at 
all  times  the  same  electrical  conditions  which  by  observation 
and  experience  he  has  found  necessary  in  order  to  obtain  a 
satisfactory  deposit  of  uniform  thickness  and  color  in  the 
shortest  possible  time. 

Fig.    50  shows   the   Western  ammeter.      The   ammeter   is 

FIG.  50. 


wk^  : 


W 


placed  in  one  conductor  only,  either  in  that  of  the  objects  or 
-of  the  anode,  and  thus  the  whole  of  the  current  must  pass 
through  it.  The  voltmeter,  however,  is  connected  with  both 
conductors.  On  the  point  where  the  electro-motive  force  is  to 
be  measured,  one  of  the  binding  posts  of  the  voltmeter  is  con- 
nected by  means  of  a  copper  wire  with  the  object-conductor, 
and  the  other,  with  the  anode-conductor. 

Fig.  51  illustrates  the  arrangement  of  the  switch-board  and 
ammeter  with  a  bath  operated  by  means  of  a  battery. 

Voltmeter  switch.  If  many  baths  are  in  operation  in  an 
-electro-plating  plant,  it  would  be  quite  an  expense  to  furnish 


148 


ELECTRO-DEPOSITION    OP    METALS. 


each  bath  with  a  special  voltmeter.  However,  this  is  unneces- 
sary, one  voltmeter  being  sufficient  for  three  or  four  baths.  In 
order  to  be  able  to  read  off  conveniently  on  the  voltmeter  the 
electro-motive  force  passing  into  one  of  these  baths,  a  switch  i& 


FIG.  51. 


required,  the  construction  of  which  will  be  seen  from  Figs.  52 
and  53. 

Fig.  52  shows  the  coupling  of  the  main  object-wire  ( — )  and 
of  the  main  anode-wire  (+),  which  will  be  referred  to  later  on, 
together  with  the  resistance  boards  Rt  and  R2)  the  voltmeter 
V,  switch  U,  and  the  two  baths.  In  Fig.  53  the  coupling  is 
enlarged,  and  upon  this  illustration  the  following  description 
is  based  :  Suppose  the  main  object-wire  and  anode-wire  to  be 
connected  with  the  corresponding  poles  of  a  dynamo-machine 
or  a  battery,  which  for  the  sake  of  a  clearer  view  is  omitted  in 
the  illustration.  The  switch  U  consists  of  a  brass  lever, 
mounted  with  a  brass  foot,  upon  a  board.  In  the  foot  is  a 


ELECTRO-PLATING    ESTABLISHMENTS. 


149 


screw,  with  which  is  connected  by  a  0.039-inch  thick  copper 
wire  one  of  the  pole-screws  of  the  voltmeter.  The  brass  handle 
slides  with  spring  pressure  upon  contact  buttons  connected  by 
copper  wire  with  the  binding-screws  1,  2,  3,  4/5  (upon  the 


FIG.  52. 


switch),  which  serve  for  the  reception  of  the  0.039-inch  thick 
insulated  wires  1,  2,  3,  4,  for  measuring  the  electro-motive 
force,  which  branch  off  from  the  various  tanks  or  resistance 
boards.  The  other  pole-screw  of  the  voltmeter  is  directly  con- 


150 


ELECTRO-DEPOSITION    OF    METALS. 


nected  with  the  main  anode-wire.  From  the  main  object-wire,, 
a  wire,  whose  cross-section  depends  on  the  strength  of  the 
working  current,  passes  to  the  screw  marked  " strong7'  of  the 
resistance  board  R^,  the  screw  marked  "  weak  "  of  the  resist- 
ance board  Rr  is  connected  by  a  wire  of  corresponding  thick- 
ness with  the  object-wire  of  bath  I,  and  at  the  same  time  with 
the  binding-screw  1  of  the  switch.  The  resistance  board  R2^ 
of  the  bath  II,  is  in  the  same  manner  connected  with  the  main 
object-wire,  the  bath,  and  the  binding-screw  2  of  the  switch ; 

FIG.  53. 


also  the  resistance  boards  R3  and  R±  of  the  baths  III  and  IV,. 
which  are  not  shown  in  the  illustration.  With  the  main 
anode-wire  each  bath  is  directly  connected  by  conducting  the 
current  to  an  anode-rod  of  the  bath  by  means  of  binding- 
screws  and  a  stout  copper  wire,  and  establishing  a  metallic 
connection  between  this  anode-rod  and  the  next  one.  How- 
ever, instead  of  connecting  both,  the  current  may  also  be  con- 
ducted from  the  main  anode-wire  to  each  anode-rod. 

In  the  illustration,  the  handle  of  the  switch  rests  upon  the- 
second  contact-button  to  the  left,  which  is  connected  with  the 


ELECTRO-PLATING    ESTABLISHMENTS.  151 

binding-screw  2  of  the  switch.  In  the  latter  is  secured  the 
wire  for  measuring  the  electro-motive  force  which  leads  from 
the  resistance  board  J?2;  hence  the  voltmeter  V  will  indicate 
the  electro-motive  force  of  the  current  at  bath  II.  Suppose 
that  bath  II  is  full  of  objects  and,  with  the  position  of  the  lever 
of  the  resistance  board  at  "  weak,"  as  shown  in  the  illustration,, 
the  voltmeter  indicates  1.5  volts,  while  the  most  suitable 
electro-motive  force  for  the  bath  is  2.5  volts,  the  handle  of  the 
switch  is  turned  to  the  left  until  the  needle  of  the  voltmeter 
indicates  the  desired  2.5  volts. 

If  the  handle  of  the  switch  U  be  turned  to  the  left  so  that  it 
rests  upon  the  contact-button  1,  the  measuring  wire  of  bath  II 
is  thrown  out,  and  the  voltmeter  indicates  the  electro-motive 
force  in  bath  I ;  if  the  lever  rests  upon  contact-button  3,  the 
electro- motive  force  in  bath  III  is  indicated,  and  so  on. 

Dependence  of  the  current-density  on  the  electro-motive  force- 
If  a  current  of  known  strength  be  at  the  outset  conducted' 
through  electrodes  of  a  certain  size  into  a  bath  of  determined 
resistance,  and  the  electrode-surfaces  be  then  doubled,  the 
current-strength  must  also  be  doubled  in  order  to  maintain  the 
same  current-density  as  before.  By  increasing  the  electrode- 
surfaces  to  twice  their  size,  the  resistance  of  the  bath  is,  how- 
ever, reduced  one-half  the  value  it  amounted  to  with  electrodes- 
of  half  the  size,  the  increased  electrode-surfaces  corresponding 
to  a  cross-section  of  the  bath-fluid  enlarged  in  the  same  pro- 
portion. 

Suppose  the  resistance  of  the  bath  with  an  electrode-surface 
of  1  square  decimeter  amounted  to  2.4  ohms,  and  the  current- 
strength,  which  in  this  case  also  represents  the  current-density, 
had  been  0.4  ampere,  an  increase  of  the  electrode-surface  to  2 
square  decimeters  will  require  a  current-strength  of  0.8  ampere, 
in  order  to  maintain  a  current-density  of  0.4  ampere  per  square 
decimeter.  The  resistance  of  the  bath  then  declines  from  2.4 
ohms  to  1.2  ohm.  According  to  the  laws  of  Ohm,  the  resist- 
ance of  2.4  ohms  required  an  electro-motive  force  of  current- 
strength  X  resistance,  hence  of  0.4  X  2.4  =  0.96  volt.  After 


152  ELECTRO-DEPOSITION    OF    METALS. 

increasing  the  electrode-surfaces  to  2  square  decim'eters  and 
raising  the  current- strength  to  0.8  ampere,  the  resistance  de- 
clined to  1.2  ohm.  The  electro-motive  force  then  amounts  to, 
0.8  X  1.2  —  0.96  volt,  hence  to  exactly  the  same  as  in  the 
first  case. 

From  this  it  follows,  that  with  an  urfaltered  electrode- 
distance,  the  current-density  remains  unchanged  with  varying 
electrode-surfaces,  if  the  electro-motive  force  at  the  bath  be 
kept  constant  at  the  same  height. 

It  is  also  obvious  that  with  an  increasing  electro-motive  force 
at  the  bath,  the  current-density  must  also  increase,  because, 
according  to  the  law  of  Ohm,  the  current-strength  is  equal  to 
the  electro-motive  force  divided  by  the  resistance.  Since  the 
latter  is  not  changed  when  the  electrode-distance  remains  the 
same,  the  quotient  will  be  adequately  larger  if  the  divisor 
remains  the  same  and  the  dividend  be  increased.  Hence  the 
current-density  becomes  greater. 

Now,  as  for  the  production  of  a  useful  deposit,  a  certain 
current-density  should  not  be  exceeded,  the  voltmeter  furnishes 
us  the  means  to  insure  against  failure  by  keeping  the  electro- 
motive force  at  the  bath  constant  with  a  varying  charge  of  the 
latter,  and  such  an  instrument  should  not  be  wanting  in  an 
electro-plating  establishment. 

Conductors.  The  most  suitable  material  for  conducting  the 
current  is  chemically  pure  copper,  its  conducting  power  being 
next  to  that  of  silver,  but  the  use  of  the  latter  noble  metal  for 
this  purpose  is  of  course  excluded  by  reason  of  its  costliness. 

The  laws  of  Ohm  have  shown  us  that  the  current-strength 
depends  on  the  magnitude  of  the  electro-motive  force  and  the 
resistance  in  the  circuit ;  the  greater  the  resistance,  the  less  the 
current-strength  which  can  flow  through  the  conductor.  From 
this  it  follows  that  in  order  to  reduce  losses  of  electro-motive 
force  to  a  minimum,  conductors  of  adequate  cross-sections 
should  be  selected. 

Conductors  which  cause  a  loss  of  more  than  10  per  cent,  of 
the  electro-motive  force  have  to  be  considered  insufficient  as 


ELECTRO-PLATING    ESTABLISHMENTS.  153 

regards  dimensions,  and  it  is  recommended  to  entrust  the 
installation  of  such  constructions  only  to  competent  hands 
capable  of  making  the  calculations  required  for  the  purpose. 

In  addition  to  the  correct  dimensions  of  the  conductors,  the 
mode  of  mounting  them  also  deserves  the  greatest  attention. 
All  the  connections  of  the  conductors,  which  are  called  contacts, 
must  be  made  in  the  most  careful  manner,  since  bad  contacts 
•cause  a  transition-resistance,  and,  in  such  a  case,  a  large 
decrease  in  electro-motive  force  could  not  be  prevented  even 
by  conductors  of  ample  dimensions. 

A  distinction  is  made  between  main  conductors  and  branch 
conductors,  the  former  effecting  the  transmission  of  the  current 
from  the  source  of  current  to  the  baths,  while  the  latter  branch 
off  from  them  to  the  separate  baths. 

The  positive  main  conductor  or  anode  conductor  is  con- 
nected with  the  +  pole  of  the  source  of  current,  and  the  nega- 
tive main  conductor  or  object-conductor  with  the  —  pole. 

Both  bare  and  insulated  conductors  are  used.  For  con- 
ductors of  larger  cross-sections,  bright  electrolytic  copper  in 
the  form  of  round  bars  or  flat  rails  is  employed,  while  for  con- 
ductors of  smaller  cross-sections,  copper  wire  covered  with  an 
insulating  material,  such  as  hemp  or  jute  coated  with  asphalt 
or  varnish  suffices.  For  connecting  certain  movable  parts 
with  the  rigid  main  conductor,  flexible  cables  of  copper  wire, 
either  bare  or  insulated,  are  very  convenient. 

Bare  conductors  must  be  fixed  in  such  a  manner  that  they 
do  not  touch  each  other,  which  would  cause  short-circuiting, 
and  possibly  danger  of  fire,  nor  come  in  contact  with  damp 
brick-work.  This  is  effected  by  placing  the  conductors  upon 
porcelain  insulators,  to  which  they  are  secured  by  wire. 

It  is  also  advisable  not  to  allow  even  thoroughly  insulated 
•conductors  to  lie  directly  one  upon  the  other,  as  the  insulation 
may  happen  to  be  damaged,  and  short-circuiting  would  result. 

As  regards  the  dimensions  of  the  conductors,  it  should,  in 
Tiew  of  the  slight  electro-motive  force  of  the  current  used  for 
electrolysis,  be  made  a  rule  to  calculate  for  every  ampere  cur- 


154  ELECTRO-DEPOSITION    OF    METALS. 

rent-strength  one  square  millimeter  of  copper  cross-section,  it 
the  entire  circuit  is  not  over  20  meters  long. 

Connection  of  main  conductors  and  branch  conductors  is- 
effected  by  inserting  the  ends  of  two  round  conductors  in 
couplings,  Fig.  54,  securing  them  by  means  of  screws,  and 
filling  any  intermediate  space  with  solder.  If  the  round  main 
conductors  are  to  be  run  at  an  angle,  the  coupling,  Fig.  55,  is 
used,  and  the  T-coupling,  Fig.  56,  is  employed  on  the  points 
from  which  branches  are  to  be  run  at  a  right  angle  from  the- 
main  conductor. 

Flat  copper  rails  are  connected  in  the  most  simple  manner 
by  means  of  a  piece  of  copper-sheet  and  screws,  the  contact 
surfaces  having  been  first  tinned  to  prevent  oxidation. 

FIG.  54.  FIG.  55.        FIG.  56. 


Tanks.  The  choice  of  material  for  the  construction  of  tanks 
to  hold  the  plating  solutions  depends  on  the  nature  and 
properties  of  the  latter. 

Solutions  containing  potassium  cyanide  require  tanks  of 
stoneware,  enameled  cast-iron  or  impregnated  wood.  Welded 
steel  tanks  constructed  by  the  oxy-acetylene  welding  process 
are  also  largely  used  for  cyanide  solutions,  soap  solutions, 
electric  cleaners,  etc.  Nickel  baths  and  other  baths  which  do- 
not  attack  pitch  and  wood  may  be  kept  in  wooden  tanks  lined 
with  pitch.  The  best  material  for  wooden  tanks  without  pitch 
lining  is  pitch-pine,  it  containing  least  tannic  acid.  Larch 
may  also  be  used,  but  is  inferior  to  pitch-pine.  Wood  which 
contains  tannic  acid  spoils  every  nickel  bath,  causing  dark 
nickeling,  so  that,  for  instance,  an  ,oak  tank  cannot  be  used. 
For  smaller  baths,  up  to  300  quarts,  the  most  advantageous 
tank  is  one  of  stoneware  or  enameled  iron. 


ELECTRO-PLATING    ESTABLISHMENTS. 


155 


Wooden  tanks  must  be  carefully  constructed,  and  should  be 
securely  clamped  together  with  strong  iron  bars,  riveted  and 
bolted,  as  shown  in  Fig.  57.  The  tank  is  then  coated  with  a 
mixture  of  equal  parts  of  pitch  and  rosin  boiled  with  a  small 
quantity  of  linseed  oil.  Another  mixture,  which  has  been 
found  to  afford  a  good  protective  covering  to  wood,  consists  of 
10  parts  of  gutta-percha,  3  of  pitch,  and  1J  each  of  stearine 
and  linseed  oil,  melted  together  and  incorporated. 

For  large  acid  copper  and  nickel  baths  wooden  tanks  lined 
with  chemically  pure  sheet-lead  about  0.118-inch  thick,  and  the 
seams  soldered  with  pure  lead,  are  quite  suitable.  Care  must,. 

FIG.  57. 


of  course,  be  taken  that  neither  the  conducting  rods  nor  the 
articles  suspended  in  the  bath  and  the  anodes  come  in  contact 
with  the  lead  lining,  and  therefore  the  conducting  rods  should 
not  be  laid  directly  upon  the  tanks,  but  placed  upon  a  few 
thick  strips  of  dry  wood.  Further,  the  anodes  should  be 
suspended  at  a  sufficient  distance  from  the  lead  lining,  be- 
cause with  too  small  a  distance,  metal  from  the  solution  is 
precipitated  upon  the  lead  lining.  The  latter  always  becomes 
electric,  which,  however,  does  not  matter,  and  if  the  anodes 
are  at  a  greater  distance  from  it  than  the  objects  no  metal  is 
precipitated  upon  it.  If  for  the  better  exhaustion  of  the  baths 
the  anodes  are  suspended  at  a  slight  distance  from  the  sides> 


156  ELECTRO-DEPOSITION    OF    METALS. 

it  is  advisable  to  protect  the  lead  lining  with  thin  wooden 
boards,  or  to  insulate  it  by  giving  it  two  coats  of  asphalt- 
lacquer.  However,  for  this  purpose  asphalt-lacquer  prepared 
'from  the  residues  of  the  tar  industry  is  not  available,  and  a 
solution  of  Syrian  asphalt,  with  a  small  quantity  of  Venice 
•turpentine  in  benzine  should  be  employed. 

Based  upon  careful  investigations,  such  lead-lined  tanks  have 
been  used  for  large  copper  and  brass  baths  containing  potassium 
cyanide  without  the  slightest  injury  to  the  baths.  If  even  a 
film  of  lead  cyanide  is  formed  upon  the  lead,  it  is  insoluble  in 
excess  of  potassium  cyanide,  and  hence  is  entirely  indifferent 
as  regards  the  bath.  However,  for  nickel  baths  containing 
large  quantities  of  acetates,  citrates  and  tartrates,  these  lead- 
lined  tanks  cannot  be  recommended,  since  these  salts  possess  a 
certain  power  of  dissolving  lead  oxide.  However,  the  use  of 
such  baths  has  been  almost  entirely  abandoned,  and  the  small 
quantities  of  organic  acid  which  occasionally  serve  for  correct- 
ing the  reaction  of  a  nickel  bath  need  not  be  taken  into  con- 
sideration. The  lead  lining  might  be  dispensed  with  if  it 
were  not  for  the  difficulty  of  keeping  wooden  tanks  tight. 
Many  plating  solutions  impair  the  swelling  power  of  the  wood, 
and  with  even  a  slight  change  in  the  temperature  the  tanks 
become  pervious,  the  evil  in  time  increasing.  Tanks  lined 
with  lead,  on  the  other  hand,  remain  tight,  and  have  the 
advantage  that  the  baths  can  be  boiled  in  them  by  means  of 
steam  introduced  through  a  lead  coil  in  the  tanks. 

For  large  baths  containing  potassium  cyanide,  holders  of 
brick  laid  in  cement  may  also  be  used,  or  holders  of  boiler- 
plate lined  with  a  layer  of  cement.  For  nickel  baths  cement- 
lined  tanks  cannot  be  recommended.  If  a  tank  of  that  kind 
is  to  be  used,  direct  contact  of  the  nickel  solution  with  the 
cement  lining  should  be  prevented  by  applying  to  the  latter 
at  least  two  coats  of  asphalt-lacquer.  Stoneware  tanks  do  not 
bear  heating. 

When  using  lead  steam  coils  or  loops  in  plating  tanks  or 
those  arranged  for  electric  cleaning,  the  coil  ends  entering  and 


ELECTRO-PLATING    ESTABLISHMENTS.  157" 

returning  from  the  solution  should  be  connected  to  the  heat- 
ing system  with  insulating  joints,  Fig.  58, 
in  order  to  prevent  leakage  of  the  electric  FIG.  58. 

current. 

Conducting  fixtures.  These  include  the 
conducting  rods  which  serve  for  suspending 
the  objects  and  anodes,  and  are  laid  across 
the  tanks,  as  well  as  the  binding-posts  and 
screws  and  copper-connections  used  for  con- 
necting the  conducting  rods. 

The  cross-sections  of  the  conducting  rods  are,  on  the  one 
hand,  dependent  on  the  maximum  current-strength  which 
without  greater  resistance  is  to  pass  through  them,  and,  on  the 
other,  on  the  weight  of  the  objects  and  anodes  to  be  suspended 
in  the  bath.  The  conducting  rods  may  be  drawn  of  hard  cop- 
per, or  for  not  considerable  current-strengths  may  be  made  of 
brass  or  copper  tubing  with  insertions  of  iron  rods.  Bi-metal,. 
i.  e.,  iron  rods  upon  which  has  been  deposited  by  electrolytic 
methods  a  coat  of  copper  adequate  to  the  current  -strength,, 
may  be  highly  recommended.  By  reason  of  the  intimate 
union  of  the  copper  with  the  iron,  the  latter  takes  part  in  the 
conduction,  which  is,  as  a  rule,  not  the  case  with  copper  tubes 
with  insertions  of  iron  rods,  in  consequence  of  the  formation 
of  oxide  and  defective  contacts. 

It  is  advantageous  to  provide  the  narrow  sides  of  the  tanks- 
with  semicircular  notches  for  the  conducting  rods  to  rest  in,  to 
prevent  their  rolling  away.  When  using  stoneware  tanks  the 
conducting  rods  are  laid  directly  upon  the  tanks.  Tanks  of 
other  material  must  be  provided  with  an  insulated  rim  of 
wood,  or  the  rods  are  insulated  by  pushing  pieces  of  rubber 
tubing  over  their  ends.  According  to  the  size  of  the  bath, 
3,  5,  7,  or  more  conducting  rods,  best  of  pure  massive  copper, 
or  if  this  is  too  expensive,  of  strong  brass  tubing  with  iron 
rods  inside,  are  used. 

The  rods  carrying  the  anodes,  as  well  as  those  carrying  the 
objects,  must  be  well  connected  with  each  other.  This  is 


158 


ELECTRO-DEPOSITION    OF    METALS. 


effected  by  means  of  binding-posts  and  screws  of  the  improved 
forms  shown  in  Fig.  59,  Nos.  1  and  2  being  rod  connections 
for  tanks.  No.  4,  or  double  connection,  is  a  very  convenient 
form,  as  it  can  be  adapted  to  so  very  many  changes.  The 


FIG.  59. 


No.  1. 


No.  3. 


No.  4. 


No.  2. 


three-way  connection,  No.  3,  is  so  well  known  that  it  hardly 
needs  an  explanation. 

Arrangement  of  objects  and  anodes  in  the  bath.  To  secure 
the  uniform  coating  of  the  objects  with  metal  they  must  be 
surrounded  as  much  as  possible  by  anodes,  i.  e.,  the  positive- 


ELECTRO-PLATING    ESTABLISHMENTS.  159 

pole  plates  of  the  metal  which  is  to  be  deposited.  For  flat 
objects,  it  suffices  to  suspend  them  between  two  parallel  rows 
of  anodes,  the  most  common  arrangement  being  to  place  three 
rods  across  the  bath,  the  two  outermost  of  which  carry  the 
anodes,  while  the  objects  are  secured  to  the  center  rod.  For 
wide  baths  five  conducting  rods  are  frequently  used,  but  they 
should  always  be  so  arranged  that  a  row  of  objects  is  between 
^two  rows  of  anodes.  The  arrangement  frequently  seen  with 
four  rods  across  the  baths,  of  which  the  outermost  carry  anodes, 
and  the  other  two,  objects,  is  irrational  if  the  objects  are  to  be 
uniformly  plated  on  all  sides,  because  the  sides  turned  towards 
the  anodes  are  coated  more  heavily  than  those  suspended 
opposite  to  the  other  row  of  objects. 

For  large  round  objects  it  is  better  to  entirely  surround 
them  with  anodes,  if.it  be  not  preferred  to  turn  them  fre- 
quently, so  that  all  sides  and  portions  gradually  feel  the  effect 
of  the  immediate  vicinity  of  the  anodes.  (See  "  Nickeling.") 

For  objects  to  be  plated  on  one  side  only  the  center  rod  may 
be  used  for  the  anodes  and  the  two  outer  ones  for  the  objects; 
ihe  surface  to  be  plated  being,  of  course,  turned  towards  the 
anodes. 

There  shonld  be  an  ample  supply  of  anodes  in  the  bath. 
In  baths  of  base  metals  the  anode-surface  should  at  least  be 
-equal  in  size  to  the  surface  to  be  plated  ;  an  exception  being 
permissible  in  gold  and  silver  baths. 

The  anodes  should  not  be  too  thin,  because  the  thinner 
ihey  are,  the  greater  the  resistance.  Copper,  brass  and  nickel 
anodes  should  not  be  less  than  3  millimeters  thick,  and  the 
hooks  by  which  they  are  suspended  should  be  correspondingly 
thick  and  riumerous. 

The  anodes  are  suspended  from  the  cross-rods  by  strong 
hooks  of  the  same  metal,  so  that  they  can  be  entirely  im- 
mersed in  the  bath  (Fig.  60).  Hooks  of  another  soluble  metal 
would  contaminate  the  bath  by  dissolving  in  it,  and  this 
must  be  strictly  avoided,  as  it  woujd  cause  all  sorts  of 
•disturbances  in  the  correct  working  of  the  bath.  In  case 


160 


ELECTRO-DEPOSITION    OF    METALS. 


FIG.  60.         FIG.  61. 


hooks  of  another  metal,  except  platinum,  are  used,  the  anodes 
must  be  suspended  so  that  they  project 
above  the  surface  of  the  liquid,  and  the 
hooks  not  being  immersed,  are  there- 
fore, not  liable  to  corrosion ;  but  the 
anodes  are  then  not  completely  used  up, 
the  portion  dipping  in  the  solution  being 
gradually  dissolved,  whilst  the  portion 
projecting  above  the  fluid  remains  intact. 
Instead  of  wire  hooks,  strips  of  the  same 
metal  as  the  anodes  and  fastened  to  them 
by  a  rivet  may  also  be  used  (Fig.  61). 

For  suspending  the  objects,  lengths  of 

soft,  pure  copper  wire,  technically  called  slinging  wires,  are 
used.  They  are  simply  suitable  lengths  of  copper  wire  of  a 
gauge  to  suit  the  work  in  hand,  wire  No.  20  Birmingham  wire 
gauge  being  generally  employed  for  such  light  work  as 
spoons,  forks  and  table  utensils.  Wire  of  a  larger  diameter 
should  be  employed  for  large  and  heavy  goods.  The  immersed 
ends  of  these  wires  becoming  coated  with  the  metal  which  is 
being  deposited,  they  should  be  carefully  set  aside  each  time 
after  use,  and  when  the  deposit  gets  thick  it  should  be  stripped 
off  in  stripping  acid,  and  the  wire  afterwards  annealed  and 
straightened  for  future  use. 

To  keep  the  rods  clean  and  to  protect  them  from  the  fluid 
draining  off  from  the  articles  when  taken  from  the  bath,  it  is 
advisable  to  cover  them  with  a  roof  of  strips  of  wood  (A),  or  a 
semi-circular  strip  of  zinc  coated  with  ebonite  lacquer ;  by  this 
means  the  frequent  scouring  of  the  rods,  which  otherwise  is 
necessary  in  order  to  secure  a  good  contact  with  the  hooks  of 
the  anodes,  is  done  away  with. 

It  need  scarcely  be  mentioned  that  the  anodes  and  the  ob- 
jects to  be  plated  must  not  touch  each  other,  as  short-circuiting 
would  take  place  on  the  point  of  contact. 

The  plating  solutions,  briefly  called  baths  or  electrolytes, 
will  be  especially  discussed  in  speaking  of  the  various  electro- 


ELECTRO-PLATING    ESTABLISHMENTS.  161 

plating  processes.  Other  rules  for  suspending  the  objects  will 
be  mentioned  under  "  Nickeling,"  and  are  valid  for  all  other 
electro-plating  processes. 

Apparatus  for  cleansing  and  rinsing.  It  remains  to  consider 
the  cleansing  and  rinsing  contrivances,  without  which  it  would 
be  impossible  to  carry  on  electro-plating  operations.  Every 
electro-plating  establishment,  no  matter  how  small,  requires  at 
least  one  tub  or  vat  in  which  the  objects  can  be  rubbed  or 
brushed  with  a  suitable  agent  in  order  to  free  them  from 
grease.  This  is  generally  done  by  placing  a  small  kettle  or 
stoneware- pot  containing  the  cleansing  material  at  the  right- 
hand  side  of  the  operator  alongside  the  vat  or  tub.  Across 
the  latter,  which  is  half  filled  with  water,  is  laid  a  board  of 
soft  wood  covered  with  cloth,  which  serves,  as  a  rest  for  the 
objects  previously  tied  to  wires.  The  objects  are  then  scrubbed 
with  a  brush,  or  rubbed  with  a  piece  of  cloth  dipped  in  the 
cleansing  agent.  The  latter  is  then  removed  by  rinsing  the 
objects  in  the  water  in  the  tub  and  drawing  them  through 
water  in  another  tub.  By  this  cleansing  process  a  thin  film 
of  oxide  is  formed  upon  the  metals,  which  would  be  an  im- 
pediment to  the  intimate  union  of  the  electro-deposit  with  the 
basis-metal.  This  film  of  oxide  has  to  be  removed  by  dipping 
or  pickling,  for  which  purpose  another  vat  or  tub  containing 
the  pickle,  the  composition  of  which  varies  according  to  the 
nature  of  the  metal,  has  to  be  provided.  After  dipping,  the 
objects  have  to  be  again  thoroughly  rinsed  in  water  to  free 
them  from  adhering  pickle,  so  that  for  the  preparatory  cleans- 
ing processes  three  vessels  with  water,  which  has  to  be  fre- 
quently renewed,  as  well  as  the  necessary  pots  for  pickling 
solutions,  have  to  be  provided. 

Larger  plants  require  a  special  table  for  freeing  the  objects 
from  grease.  Such  a  table  is  shown  in  Fig.  62.  It  consists  of  a 
box  furnished  with  legs,  and  is  divided  by  four  partitions  into 
two  larger  and  three  smaller  compartments.  Boards  covered 
with  cloth  are  laid  over  the  larger  compartments,  upon  which 
the  objects  are  brushed  with  lime-paste  for  the  final  thorough 
11 


162 


ELECTRO-DEPOSITION    OF    METALS. 


freeing  from  grease.  Over  each  of  these  compartments  is  a 
rose  provided  with  a  cock,  under  which  the  objects  are  rinsed 
with  water.  The  outlets  for  the  waste  water  from  the  large 
compartments  are  in  the  bottom  of  the  box  and  are  provided 
with  valves.  Of  the  smaller  compartments,  the  one  in  the 
center  serves  for  the  reception  of  the  lime-paste  (see  "  Chemi- 
cal Treatment "),  while  the  others  contain  each  two  pots  or 
small  stoneware  tanks  with  pickling  fluid.  In  Fig.  66  these 

FIG.  62. 


tanks  are  indicated  by  11  and  12.  The  two  marked  11  con- 
tain dilute  sulphuric  acid  for  pickling  iron  and  steel  articles, 
while  those  marked  12  contain  dilute  potassium  cyanide  solu- 
tion for  pickling  copper  and  its  alloys,  and  Britannia,  etc. 
For  cleansing  smaller  articles,  four  men  can  at  one  time  work 
on  such  a  table;  but  for  cleansing  larger  articles  only  two. 
For  an  establishment  which  does  not  require  such  a  large 
table,  one  with  a  larger  and  two  smaller,  compartments  may 
be  used.  The  advantages  of  such  a  box-table  are  that  every- 


ELECTRO-PLATING    ESTABLISHMENTS.  163 

;thing  is  handy  together  ;  that  the  pickle,  in  case  a  pot  should 
break,  cannot  run  over  the  floor  of  the  workshop ;  and  that 
"the  latter  is  not  ruined  by  pickle  dropping  from  the  objects. 
The  small  box  on  the  side  of  the  table  serves  for  the  reception 
of  the  various  scratch-brushes. 

After  having  received  the  electro-deposit,  the  objects  have 
to  be  again  rinsed  in  cold  water,  which  can  be  done  in  one  of 
<the  three  tanks  or  with  the  rose-jet,  and  finally  have  to  be 
immersed  in  hot  water  until  they  have  acquired  the  tempera- 
ture of  the  latter.  How  the  water  is  heated  makes  no  dif- 

FIG.  63. 


•ference,  and  depends  on  the  size  of  the  establishment.  The 
heated  objects  are  then  immediately  dried  in  a  box  filled  with 
dry,  fine  sawdust  that  of  boxwood,  maple,  or  other  wood  free 
from  tannin  being  suitable  for  the  purpose.  A  steam  sawdust 
box  very  suitable  for  the  purpose  is  made  in  four  removable 
sections,  which  consist  of  a  smooth  galvanized  iron  box,  hot 
air  chamber  with  asbestos  lining  closely  built,  f -inch  steam 
radiator,  and  a  rigid  stand  made  of  1  J-inch  angle  iron. 

To  overcome  various   troubles   and  difficulties  connected 


-164  ELECTRO-DEPOSITION    OF    METALS.    . 

with  drying  by  means  of  sawdust  mixed  with  the  articles: 
placed  in  the  pan  and  heated,  steam  drying  barrels  have  been 
introduced.  One  type  is  practically  the  same  as  the  oblique 
tilting  tumbling  barrel  in  common  use  for  cleaning  metallic 
surfaces,  except  that  it  is  jacketed  and  otherwise  constructed 
to  allow  a  circulation  of  steam  about  the  inner  barrel,  auto- 
matic ejection  of  the  condensation,  still  allowing  the  barrel  to 
be  tilted.  A  barrel  load  can  be  thoroughly  dried  in  a  few 
minutes,  especially  if  the  work  is  shaken  out  of  hot  water. 
•It  will  be  readily  understood  that  the  rolling  over  and  over 
of  the  hot  barrel  thoroughly  mixes  the  work  and  sawdust, 
liberates  the  steam  and  precludes  the  possibility  of  water- 
marks, etc.,  and  further,  brightens  the  goods  at  the  same  time. 
A  centrifugal  dryer  for  small  work,  supplied  by  The  Han- 
son &  Van  Winkle  Co.,  N.  J.,  is  shown  in  Fig.  63.  This 
machine  should  be  used  where  mechanical  plating  apparatus 
is  installed,  one  to  three  minutes  only  being  necessary  for 
drying  small  work.  The  machine  is  furnished  with  or  with- 
out hoist,  and  is  fitted  with  ball  bearings.  It  can  be  supplied 
with  a  tapered  steel  pan  or  a  perforated  straight-sided  steel  or 
copper  basket  for  holding  the  work. 

B.  INSTALLATIONS  WITH  DYNAMO-ELECTRIC  MACHINES. 

Setting  up  and  running  a  dynamo.     Most   of  the   troubles^ 
with  plating-dynamos  are  caused  by  neglecting  one  or  more  of 
the  conditions  necessary  for  their  proper  operation,  and  are 
not  due  to  any   defects  in  the  machines  themselves.     The 
troubles  most  frequently  encountered  are,  in  order  of  their 
frequency,  as  follows :    First,  insufficient  or  variable  speed. 
Second,  improper  setting  of  the  brushes,  and  the  use  of  im- 
proper lubricants  and  cleaning  material  on  the  commutator. 
Third,  poor  oil,  or  an  insufficient,  or  too  great,  an  amount  of 
.oil  in  the  bearings.     Fourth,  overloading  the  machine. 

It  is  important  that  the  dynamo  be  properly  placed,  and  the 
following  considerations  should  govern  the  choice  of  location  : 
The  dynamo  should  not  be  exposed  to  moisture  nor  to  the  dirt 


ELECTRO-PLATING    ESTABLISHMENTS.  165 

•and  dust  of  the  polishing  room.  Cleanliness  is  a  necessity. 
A  cool,  well-ventilated  room  should  be  chosen.  This  is  im- 
portant, for  a  well- ventilated  machine  will  do  more  work  with 
less  wear  on  parts  than  one  unfavorably  placed.  The  machine 
should  not  be  boxed  in,  as  this  will  make  it  run  hotter  than  it 
otherwise  would.  Not  only  this,  the  mere  fact  of  having  it 
totally  boxed  in  precludes  the  probability  of  receiving  the 
proper  amount  of  attention. 

Except  on  the  larger  sizes  of  machines  a  special  foundation 
is  not  mechanically  necessary,  providing  the  floor  is  fairly 
solid.  On  account,  however,  of  dirt  getting  into  the  running 
parts  when  the  floor  is  cleaned,  it  is  always  well  to  raise  the 
machine  from  six  to  twelve  inches  above  the  floor.  For  a 
small  dynamo  a  well-made  box  of  two-inch  lumber  will  afford 
an  ample  foundation.  For  the  larger  sizes  two  or  three  strips 
of  6-inch  x  6-inch  yellow  pine  may  be  used.  In  either  case 
the  box  or  strips  should  be  solidly  nailed  or  bolted  to  the  floor 
and  the  machine  secured  to  its  base  with  four  lag  screws  of 
the  proper  size. 

The  direction  of  rotation  may  be  ascertained  by  an  inspec- 
tion of  the  brushes,  the  commutator  running  away  from  the 
brushes.  One  of  the  troubles  mentioned  above,  namely,  vari- 
able speed,  may  be  remedied  to  a  large  extent  by  a  suitable 
belt,  run  in  the  proper  manner.  The  counter-shaft  should 
never  be  run  directly  over  the  dynamo,  but  should  be  placed 
far  enough  to  one  side  so  that  the  belt  will  run  diagonally  and 
in  such  a  direction  that  the  under  side  of  the  belt  does  the 
work.  This  is  on  account  of  the  fact  that  when  the  belt  is 
running  vertically  or  diagonally  with  the  upper  side  doing 
the  work  it  stretches  and  sags  away  from  the  pulley  when  a 
heavy  load  is  thrown  on  the  dynamo,  thus  giving  less  pull  as 
the  necessity  for  a  greater  pull  increases.  Use  good,  pliable, 
single  belting  with  the  hair  side  of  the  belt  to  the  pulley  on 
smaller  and  medium-size  machines.  For  the  larger  sizes  a 
thin,  double  belt  may  be  used. 

After  the  machine  has  been  properly  set  and  belted,  it  re- 


166  ELECTRO-DEPOSITION    OF    METALS. 

mains  to  start  it  up.  Before  starting,  remove  the  bearing  caps 
and  pour  a  small  quantity  of  oil  on  the  bearings ;  loosen  the 
screw  holding  the  rocker-arm  in  position,  and  be  prepared  to 
shift  the  rocker-arm  backward  or  forward,  so  as  to  get  the 
brushes  on  the  neutral  or  non-sparking  line,  as  it  often  happens 
that  the  rocker-arm  has  been  shifted  from  its  proper  position 
in  transportation. 

The  proper  position  for  the  tips  of  the  brushes  on  all  ma- 
chines of  either  the  bipolar  or  multipolar  type  is  about  opposite 
the  center  of  the  poles.  The  tips  of  the  brushes  should  also  be 
spaced  at  even  intervals,  this  being,  on  the  two-pole  machine, 
diametrically  opposite  to  each  other;  on  the  four-pole  machine 
one-quarter  of  the  circumference  from  each  other ;  on  the  six- 
pole  machine,  one-sixth  of  the  circumference,  and  so  on.  The 
exact  position  of  the  brushes  (that  is,  where  they  run  spark- 
lessly)  can  only  be  ascertained  by  trial.  This  adjustment  should 
be  made,  in  case  it  is  necessary,  as  soon  as  the.  machine  starts 
up,  for  if  it  is  allowed  to  run  any  length  of  time  while  sparking 
the  commutator  will  be  cut  badly,  and  may  necessitate  taking 
out  the  armature  and  truing  up  the  commutator.  In  case  this 
is  necessary,  a  sharp  diamond-point  tool  should  be  used  with  a 
moderate  speed,  and  the  commutator  should  be  finished  with  a 
fine  second-cut  file,  and  then  with  No.  0  sandpaper  and  oil. 
After  the  proper  adjustment  of  the  brushes  has  been  made, 
take  an  oil-can,  and  while  the  machine  is  running,  pour  oil 
slowly  into  the  oil-well  until  the  oil-rings  take  it  up  properly 
and  carry  it  to  the  top  of  the  bearings,  where  it  enters  the  dis- 
tributing slot.  If  too  little  oil  is  in  the  well  and  the  rings  do- 
not  dip  into  it  sufficiently  deep,  they  will  rattle  around  and 
spatter  oil,  whereas  if  too  much  oil  is  put  in,  it  will  run  out  at 
the  ends  of  the  bearings  and  get  into  the  belt,  winding  and 
commutator  of  the  machine. 

While  the  commutator  should  never  be  allowed  to  become 
greasy  or  dirty,  it  is  equally  important  that  it  should  not  be 
run  perfectly  dry,  so  that  the  brushes  cut.  When  it  becomes 
dirty,  after  cleaning  with  No.  0  sandpaper  (emery  should 


ELECTRO-PLATING    ESTABLISHMENTS.  167 

never  be  used)  it  should  be  re-oiled  by  rubbing  it  with  a 
woolen  cloth  moistened  with  kerosene  oil,  or  with  the  very 
smallest  amount  of  lubricating  oil.  The  quality  and  kind  of 
oil  used  for  the  bearings  is  important,  and  a  regular  dynamo 
oil  should  be  used.  Under  no  circumstances  should  vegetable 
or  animal  oil  (such  as  castor  or  sperm  oil)  be  used,  but  a  light 
grade  of  mineral  dynamo  oil. 

The  brushes  should  not  only  be  properly  set  as  regards  their 
position  around  the  commutator,  but  they  should  have  careful 
individual  setting.  They  should  have  a  fair  and  even  bedding 
on  the  commutator,  and  not  touch  on  the  heel  or  toe  or  on 
either  edge,  as  the  object  is  to  get  full  contact  surface  between 
the  brushes  and  the  commutator.  If  the  commutator  is  kept 
in  proper  shape  and  the  brushes  once  properly  set,  it  will  not 
be  necessary  to  adjust  them  often.  As  it  is  practically  impos- 
sible to  make  a  perfectly  accurate  setting  of  the  brushes,  and 
it  takes  them  some  few  days  to  get  worn  down  to  a  good  con- 
tact, it  will  be  seen  that  it  does  more  harm  than  good  to  be 
continually  re-setting  them.  If  the  ends  of  the  brushes  get 
very  ragged,  they  should,  in  the  case  of  wire-gauze  brushes, 
be  carefully  trimmed  with  a  pair  of  shears,  and  in  the  case  of 
strip-copper  brushes,  filed  with  a  fine  second-cut  file.  The 
tension  spring  on  the  brush  holder  should  be  adjusted  to  make 
a  light  but  positive  contact,  for  if  there  is  too  much  pressure, 
the  brushes  will  cut  the  commutator,  causing  it  to  wear  away 
rapidly. 

If  there  is  any  doubt  about  which  is  the  positive  and  which 
is  the  negative  pole  of  the  dynamo,  the  polarity  may  be  readily 
determined  after  starting  up,  by  running  two  small  wires  from 
the  dynamo  and  placing  the  ends  in  a  glass  of  acidulated 
water.  Around  one  of  these  wires  more  bubbles  of  gas  will 
be  thrown  off  than  around  the  other,  the  one  evolving  the 
greater  amount  of  gas  being  the  negative  pole,  to  which  the 
work  should  be  attached. 

Choice  of  a  dynamo.  For  electrolytic  processes,  as  previ- 
ously mentioned,  shunt-wound  and  compound-wound  dynamos 


168  ELECTRO-DEPOSITION    OF    METALS. 

are  at  present  largely  used.  Their  construction  has  already 
been  explained,  and  there  remains  now  only  the  question 
what  size  dynamo,  i.  e.,  of  what  capacity  as  regards  current- 
strength  and  electro-motive  force,  is  to  be  selected  for  a  plant. 

We  have  learned  that  a  certain  object-surface  requires  a 
certain  current-strength.  Hence  for  plants  with  different 
baths,  it  is  only  necessary  to  fix  the  largest  object-surface  in 
square  decimeters  which  is  to  be  suspended  in  the  separate 
baths  and  to  multiply  this  number  of  square  decimeters  by 
the  current-density  in  amperes,  in  order  to  find  the  supply  of 
current  required  for  each  bath.  The  sum  of  the  current  re- 
quired for  the  separate  bath,  with  an  allowance  of  20  to  25 
per  cent,  for  an  eventual  enlargement,  gives  the  current- 
strength  the  dynamo  must  furnish.  It  must  of  course  be  taken 
into  consideration  whether  all  the  baths  are  to  be  in  constant 
operation  at  the  same  time  or  not.  In  the  latter  case  a  smaller 
current-strength  will  of  course  suffice,  and  a  smaller  type  of 
dynamo  answer  the  purpose. 

The  impressed  electro-motive  force  of  the  dynamo  should  be 
such  that,  taking  into  consideration  the  decline  of  the  electro- 
motive force  in  the  conductors,  it  is,  at  the  greatest  current- 
capacity,  about  J  to  J  volt  greater  than  the  highest  electro- 
motive force  of  a  bath  required. 

For  the  purpose  of  explaining  by  an  example  the  choice  of 
a  suitable  dynamo,  let  us  suppose  that  a  nickel  bath  with  an 
object  surface  of  50  sq.  decimeters ;  a  potassium  cyanide 
copper  bath"  with  an  object  surface  of  30  sq.  decimeters ;  a 
brass  bath  with  an  object  surface  of  40  sq.  decimeters;  a  silver 
bath  with  an  object  surface  of  10  sq.  decimeters,  are  to  be  fed 
with  current. 

The  standard  current-densities  and  electro-motive  forces  re- 
quired for  the  separate  baths  are  given  later  on  when  speaking 
of  them.  It  will  there  be  found  that  the  current-density  for 
nickeling  brass  amounts  to  about  0.4  ampere,  the  electro- 
motive force  being  2.5  volts ;  for  coppering,  0.35  ampere  and 
3.0  to  3.5  volts  are  required  ;  for  brassing  also  0.35  ampere 


ELECTRO-PLATING    ESTABLISHMENTS.  169 

and  3.0  to  3.25  volts  ;  while  for  silvering  0.2  ampere  and  1 
volt  are  on  an  average  used.     This  amounts  to 

For  nickel  bath  50  sq.  decimeters  X  0.4  amp&re  =  20  amperes. 
For  copper  bath  30  sq.  decimeters  X  0.35  ampere  =  10.5  amperes. 
For  brass  bath  40  sq.  decimeters  X  0-35  ampere  —  14  amperes. 
For  silver  bath  10  sq.  decimeters  X  0.2  ampere  =  2  amperes. 


46.5  amperes. 

Hence  46.5  amperes  are  required  for  the  simultaneous 
-operation  of  these  four  baths,  and  a  dynamo  of  50  amperes 
current-strength  and  4  volts  impressed  electro-motive  force 
would  have  to  be  selected,  since,  taking  into  consideration,  a 
permissible  decline  of  electro-motive  force  of  10  per  cent.  = 
0.4  volt  in  the  conductors,  there  are  still  at  disposal  3.6  volts, 
while  the  greatest  electro-motive  force  required  amounts  to 
3.5  volts. 

Since  the  various  baths  of  a  larger  establishment  possess 
different  resistances  and  cannot  always  be  charged  with  the 
same  object-surfaces,  they  have  to  be  operated  in  parallel. 
This  renders  it  necessary  that  for  each  separate  bath  working 
with  a  lower  electro-motive  force,  the  excess  of  electro-motive 
force  as  existing  in  the  main  conductor  has  to  be  destroyed  by 
a  resistance,  called  the  main-current  regulator  or  bath-current 
regulator.  Hence  as  many  main-current  regulators  must  be 
provided  as  there  are  baths,  and  the  regulators  have  to  be 
exactly  calculated  and  constructed  for  the  required  effect. 
Thus  in  the  above-mentioned  example,  the  bath-current  regu- 
lators, with  an  electro-motive  force  of  3.6  volts  in  the  main 
conductor,  must  let  pass  for  a  nickel  bath  20  amperes  and 
destroy  1.1  volts  ;  let  pass  for  a  copper  bath  10.5  amperes  and 
destroy  0.6  to  0.35  volt  ;  let  pass  for  a  brass  bath  14  amperes 
and  destroy  0.6  to  0.35  volt  ;  let  pass  for  a  silver  bath  2  amperes 
and  destroy  2.6  volts. 

Since  every  destruction  of  electro-motive  force  means  an 
economic  loss,  it  follows  that  the  impressed  electro-  motive  force 
of  the  dynamo  should  not  be  greater  than  absolutely  necessary, 


170  ELECTRO-DEPOSITION    OF    METALS. 

so  that  it  can  be  reduced  by  a  regulator  to  the  lowest  per- 
missible limit,  and  this  limit  should  be  constantly  maintained. 
Thus,  when  the  electrode  surfaces  in  the  bath  are  changed, 
and  there  is  consequently  also  a  change  in  the  impressed 
electro-motive  force,  the  latter  can  be  properly  adjusted  by  the 
regulator.  If  this  were  not  done,  and  the  impressed  electro- 
motive force  would  become  considerably  greater,  the  bath- 
current  regulators  calculated  for  the  destruction  of  a  fixed 
electro-motive  force  would  no  longer  be  capable  of  fulfilling 
their  objects  From  what  has  been  said,  it  will  be  seen  that 
voltmeters  are  indispensable  for  electro-plating  plants  in  order 
to  be  constantly  informed  as  to  the  electro-motive  force  pre- 
vailing at  the  baths,  and,  if  necessary,  to  correct  it. 

By  reason  of  the  economic  loss  connected  with  the  destruc- 
tion of  an  excess  of  electro-motive  force,  it  may  also  have  to 
be  taken  into  consideration  whether  in  larger  plants  it  would 
not  be  better  to  use  several  dynamos  with  different  impressed 
electro-motive  forces  than  a  single  dynamo  with  an  impressed 
electro-motive  force  required  for  the  greatest  electro-motive 
force  for  the  baths.  Suppose,  for  instance,  there  are  present 
in  a  larger  plant,  in  addition  to  nickel,  brass  and  copper 
cyanide  baths,  which  require  a  voltage  of  up  to  3J  volts,  a 
large  number  of  silver  and  tin  baths  and  acid  copper  baths 
for  galvanoplasty  (with  the  exception  of  those  for  rapid  gal- 
vanoplasty),  for  which  an  impressed  electro-motive  force  of  2 
volts  is  quite  sufficient,  it  would  by  all  means  be  more  judic- 
ious to  use  for  the  first-named  baths  a  special  dynamo  with 
an  impressed  electro-motive  force  of  4  volts,  and  for  the  last- 
mentioned  baths  a  dynamo  with  a  voltage  of  2  volts. 

Another  question  to  be  considered  in  the  choice  of  a  dynamo 
is,  whether  one  or  several  accumulator  cells  are  to  be  charged 
from  it.  This  will  be  later  on  referred  to. 

While,  when  baths  are  coupled  in  parallel,  each  bath  receives 
its  supply  of  current  from  the  main  conductor,  and  such  parallel 
coupling  is  always  required  when  baths  of  different  nature,  with 
unequal  resistances  and  unequal  electro  surfaces,  are  con- 


ELECTRO-PLATING    ESTABLISHMENTS. 


171 


nected,  baths  requiring  an  equal,  or  approximately  equal,, 
current-strength  may  be  coupled  one  after  the  other,  i.  e.,  in 
series.  This  principle  of  series-coupling  of  baths  is  illustrated 
by  Fig.  64. 

The  current  passes  through  the  anodes  of  the  first  bath  into 
the  electrolyte,  flows  through  the  latter  and  passes  out  through 
the  object-wire.  From  there  it  goes  through  the  anodes  of  the 
next  bath  to  the  objects  contained  in  it,  and  so  on,  until  it 
returns  through  the  object-wire  of  the  last  bath  to  the  source 
of  current. 

Thus  for  series  coupling  of  the  baths,  a  dynamo  with  a 

FIG.  64. 


greater  impressed  electro-motive  force  than  the  sum  of  the 
electro-motive  forces  of  all  the  baths  coupled  one  after  the 
other  has  to  be  selected.  On  the  other  hand,  baths  coupled 
one  after  the  other  do  not  require  a  greater  current-strength 
than  a  single  bath.  Suppose,  four  baths,  each  charged  with 
100  square  decimeters  of  cathode-  and  anode-surfaces  are 
coupled  one  after  the  other,  and  the  electro-motive  force  of 
one  bath  amounts  to  1.25  volts  and  the  current-density  to  2 
amperes.  Then  there  will  be  required  for  one  bath  100  X  2 
=  200  amperes  and  1.25  volts,  and  for  four  baths  coupled  one 
after  another,  200  amperes  and  1.25  X  4  =  5  volts. 

The  connection  of  the  baths,  resistance  boards  and  measur- 
ing instruments  to  a  shunt-wound  dynamo  is  shown  in  Fig. 


172  ELECTRO-DEPOSITION    OF    METALS. 

65,  and  requires  no  further  explanation.  The  resistance 
board  at  the  right  is  the  field  resistance  board,  the  other  two 
belonging  to  the  two  baths  which  are  coupled  in  parallel. 

Parallel  coupling  and  series  coupling  of  dynamo-machines. 
In  establishing  a  larger  electro-plating  plant,  the  question 
may  arise  whether  it  would  not  be  advisable  to  install  two 
smaller  dynamos  instead  of  a  single  larger  one  capable  of  fill- 
ing all  demands,  even  at  the  busiest  season.  The  installation 
of  two  dynamos  allows  of  the  business  being  carried  on  with- 
out serious  interruption  in  case  one  of  the  machines  requires 
repairing,  and  in  dull  times  one  dynamo  would,  as  a  rule,  be 
sufficient.  In  case  two  dynamos  are  installed,  the  main  con- 
ductors must  of  course  have  the  required  cross-sections  corre- 
sponding to  the  total  current-strength  of  both  machines. 

It,  however,  happens  very  frequently  that  as  the  plant  be- 
comes larger  by  reason  of  an  increase  in  the  number  of  baths, 
a  larger  supply  of  current  will  in  time  be  required.  The 
question  then  arises  whether  to  sell  the  old  dynamo,  which 
may  be  difficult,  especially  if  it  is  of  an  obsolete  pattern,  or 
whether  to  supply  the  deficit  of  current  by  installing  an  ad- 
ditional dynamo.  In  such  case,  if  the  baths  are  not  to  be 
divided  into  groups,  one  of  them  being  furnished  with  current 
from  one  dynamo  and  the  other  from  the  second  machine, 
but  both  the  dynamos  are  to  be  connected  to  a  common  main 
conductor,  the  cross-section  of  the  latter  must  first  of  all  be 
increased  so  as  to  be  capable  of  carrying  the  total  current- 
strength  of  both  dynamos  without  material  decrease  in  electro- 
motive force.  Whether  for  this  purpose  a  new  conductor  of 
larger  cross-section  is  to  be  used,  or  whether  a  supplementary 
conductor  is  in  a  suitable  manner  to  be  connected  with  the 
old  one,  is  best  left  to  the  judgment  of  the  person  entrusted 
with  the  installation. 

In  coupling  several  dynamos  in  parallel  to  a  common  con- 
ductor, care  must  in  all  cases  be  taken  to  connect  a  dynamo  to 
one  already  in  operation  only  after  it  had  been  excited  to  the 
same  voltage.  If  this  were  not  done,  the  current  of  greater 


ELECTRO-PLATING    ESTABLISHMENTS. 


173 


174  ELECTRO-DEPOSITION    OF    METALS. 

electro-motive  force  of  the  dynamo  in  operation  would  flow 
from  the  main  conductor  to  the  other  dynamo,  and  the  first 
dynamo  would  thus  be  short-circuited  by  the  brushes,  com- 
mutator and  armature  of  the  second  one.  No  current  would 
pass  into  the  baths,  but  the  second  dynamo  would  run  as  a 
motor.  To  prevent  this,  a  switch  has  to  be  placed  between 
every  dynamo  and  the  main  conductor.  If  one  dynamo 
already  furnishes  current,  the  second  dynamo  has  at  first  to  be 
set  in  operation  with  the  switch  open,  until  its  voltmeter  shows 
the  same  voltage  as  possessed  by  the  other  dynamo.  The 
switch  is  then  closed,  and  the  desired  current-strength  gen- 
erated by  means  of  the  shunt-regulator.  It  is  obvious  that  for 
coupling  in  parallel,  only  dynamos  which  yield  the  same 
voltage  are  suitable,  while  a  difference  in  capacity  as  regards 
current-strength  is  no  obstacle. 

The  poles  of  a  similar  name  of  the  various  machines  must 
of  course  be  connected  to  'one  and  the  same  circuit. 

Coupling  of  dynamos  in  series  may  become  necessary  when 
baths  require  a  greater  electro-motive  force  than  can  be  fur- 
nished by  a  single  machine,  for  instance,  in  case  baths  are 
coupled  one  after  the  other.  For  coupling  in  series  only 
dynamos  which  furnish  with  the  same  voltage  the  same  current- 
strength  are  suitable.  Coupling  is  effected  so  that  the  -f-  pole 
of  one  dynamo  is  connected  with  the  —  pole  of  the  other  one, 
hence  in  the  same  manner  as  cells  and  accumulators  are 
coupled. 

Coupling  in  series  of  dynamos  may  also  be  used  if  there  are 
baths  requiring  great  electro-motive  force,  for  instance,  for 
plating  en  masse  in  the  mechanical  apparatus  (see  later  on), 
while  baths  requiring  a  considerably  lower  electro-motive  force 
are  to  be  fed  from  the  same  source  of  current. 

In  such  case  it  is  advisable  to  construct  the  conductors 
according  to  the  three-wire  system.  One  conductor  is 
branched  off  from  the  +  pole  of  one  dynamo,  the  second  from 
the  —  pole  of  the  other  dynamo,  and  the  third,  called  the 
neutral  or  middle  conductor,  from  the  junction  of  the  dyna- 


ELECTRO-PLATING    ESTABLISHMENTS.  175 

mos  coupled  in  series.  Between  the  last-mentioned  neutral 
-conductor  and  an  outside  conductor  is  the  lower  electro- 
motive force  as  furnished  by  one  dynamo,  but  between  the 
two  outside  conductors,  the  sum  of  the  electro-motive  forces  of 
both  dynamos.  Hence  the  baths  requiring  a  large  electro- 
motive force  are  to  be  coupled  between  the  outside  conductors, 
and  the  baths  requiring  a  low  electro-motive  force  between  an 
outside  and  the  neutral  conductor. 

Ground  plan  of  an  electro-plating  plant  with  dynamo.  This 
in  the  most  simple  form  is  shown  in  Fig.  66.  In  order  to 
make  the  sketch  more  distinct,  the  measuring  instruments 
have  been  omitted.  Their  arrangement  will  be  understood 
from  what  has  been  previously  said,  and  from  Fig.  66. 

NN1  is  a  dynamo-electric  machine  of  older  construction. 
The  resistance-board  belonging  to  the  machine,  which  is 
placed  in  the  conductor,  is  indicated  by  No.  1,  and  is  screwed 
to  the  wall.  The  main  conductors,  marked  —  and  -f,  run 
along  the  wall,  from  which  they  are  separated  by  wood,  and 
-consist  of  rods  of  pure  copper  0.59  inch  in  diameter.  The 
rods  are  connected  with  each  other  by  brass  coupling-boxes 
with  screws.  From  the  negative  pole  and  the  positive  pole  of 
the  machine  to  the  object-wire  and  anode-wire  lead  two  wires, 
each  0.27  inch  in  diameter ;  one  end  of  each  is  bent  to  a  flat 
loop  and  secured  under  the  pole-screws  of  the  machine,  while 
the  other  ends  are  screwed  into  the  second  bore  of  the  binding- 
screws  screwed  upon  each  conductor.  To  the  right  and  left  of 
the  machine  the  baths  are  placed,  Zn,  indicating  zinc  bath  ; 
Ni  Ni,  nickel  baths  ;  Ku,  copper  cyanide  bath  ;  Mg,  brass 
bath  ;  S  K,  acid  copper  bath  ;  Si,  silver  bath  ;  and  Go,  gold 
bath.  Each  of  the  first-named  five  baths  has  its  own  resist- 
ance-board, designated  by  2,  3,  4,  5,  6.  However,  before 
reaching  the  acid  copper  bath,  and  the  silver  and  gold  baths, 
the  current  is  conducted  through  two  resistance-boards,  7  and 
8.  Since  these  baths  require  a  current  of  only  slight  electro- 
motive force,  it  is  necessary  to  place  two,  and  in  many  cases 
•even  three  or  four  resistance-boards,  one  after  another,  unless 


176 


ELECTRO-DEPOSITION    OF    METALS. 


it  be  preferred  to  feed  these  baths  with  a  special  machine  of 
less  voltage. 


FIG.  66. 


ELECTRO-PLATING    ESTABLISHMENTS.  177 

From  Fig.  66  it  will  be  seen  that  the  current  weakened  by 
the  resistance-boards  7  and  8  serves  for  conjointly  feeding  the 
acid-copper,  silver,  and  gold  baths.  Hence,  practically,  only 
one  bath  can  be  allowed  to  work  at  one  time,  as  otherwise 
each  bath  would  have  to  be  provided  with  as  many  resistance- 
boards  as  would  be  required  for  the  reduction  of  the  electro- 
motive force.  For  want  of  space  the  gold  bath  is  placed  in 
the  sketch  behind  the  silver  bath  ;  but  as  their  resistances  are 
not  the  same,  they  must  also  be  placed  parallel. 

L  is  the  lye-kettle.  It  serves  for  cleansing  the  objects  by 
means  of  hot  caustic  potash  or  soda  lye,  from  grinding  and 
polishing  dirt  and  oil.  For  larger  plants  the  use  of  a  jacketed 
kettle  is  advisable.  By  the  introduction  of  steam  in  the  jacket 
the  lye  is  heated  without  being  diluted.  The  same  object  is 
attained  by  placing  a  steam  coil  upon  the  bottom  of  the  kettle. 
Of  course,  heating  may  also  be  effected  by  a  direct  fire.  In- 
stead of  the  preparatory  cleansing  with  hot  lye,  which  saponi- 
fies the  oil.  the  objects  may  be  brushed  off  with  benzine,  oil  of 
turpentine  or  petroleum,  the  principal  thing  being  the  re- 
moval of  the  greater  portion  of  the  grease  and  dirt,  so  that  the 
final  cleansing,  which  is  effected  with  lime  paste,  may  not  re- 
quire too  much  time  and  labor.  It  is  also  advisable  to  cleanse 
the  objects,  in  one  way  or  the  other,  immediately  after  grind- 
ing, as  the  dirt,  which  forms  a  sort  of  solid  crust  with  the  oil, 
is  difficult  to  soften  and  to  remove  when  once  hard. 

The  table  which  serves  for  the  further  cleansing  of  the 
objects  has  already  been  described  on  p.  161,  and  illustrated 
by  Fig.  62. 

Referring  again  to  Fig.  66,  between  the  lye-kettle  L  and  the 
box-table,  is  a  frame,  14,  for  the  reception  of  brass  and  copper 
wire  hooks  of  various  sizes  and  shapes  suitable  for  suspending 
the  objects  in  the  bath. 

The  reservoir  W,  filled  with  water,  standing  in  front  of  the 
machine,  serves  for  the  reception  of  the  cleansed  and  pickled 
objects,  if  for  some  reason  or  other  they  cannot  be  immediately 
brought  into  the  bath. 
12 


178 


ELECTRO-DEPOSITION    OF    METALS. 


H  W  is  the  hot-water  reservoir  in  which  the  plated  objects 
are  heated  to  the  temperature  of  the  hot  water,  so  that  they 
may  quickly  dry  in  the  subsequent  rubbing  in  the  saw-dust 


£M5 


o  a: 

Z    2 


¥  LJ    CC 

i-         y 


box  /Sp.  Before  polishing  the  deposits,  iron  and  steel  objects 
are  thoroughly  dried  in  the  drying  chamber  T(Fig.  66),  heated 
either  by  steam  or  direct  fire.  By  finally  adding  to  the  appli- 


ELECTRO-PLATING    ESTABLISHMENTS. 


179 


ances  a  large  table,  13,  for  sorting  and  tying  the  objects  on  the 
copper  wires,  and  a  few  shelves  not  shown  in  the  illustration, 
everything  necessary  for  operating  without  disturbance  will 
have  been  provided. 


Figs.  67a  and  67b  show  a  plating  room  and  method  of  con- 
necting dynamo,  tanks  and  instruments  according  to  the  two- 


180  ELECTRO-DEPOSITION    OF    METALS, 

wire  system  as  fitted  up  by  The  Hanson  &  Van  Winkle  Co., 
Newark,  N.  J.  The  arrangement  will  be  readily  understood 
from  the  illustrations,  so  that  a  detailed  description  is  not 
necessary. 

The  three-wire  system  of  current  distribution  has  been  generally 
adopted  in  the  larger  plants  where  a  variety  of  solutions  are 
in  use.  The  necessity  of  shortening  time  for  deposit  without 
deterioration  of  the  quality  of  work  has  been  apparent;  this 
condition  is  effected  through  the  agitation  of  the  solution,  and 
the  consequent  employment  of  a  higher  voltage,  with  propor- 
tionate increase  in  the  ampere  current.  The  majority  of 
plating  dynamos  in  use  are  capable  of  delivering  4  to  6  volts 
only,  and  their  use  precludes  the  adoption  of  the  newer  labor- 
saving  method.  To  meet  the  demands  for  a  generator  that 
will  deliver  a  higher  range  of  voltage,  dynamos  operating 
on  the  three-wire  system  are  built  which  will  deliver  a  range 
of  voltage  up  to  12  volts  or  higher,  if  so  desired.  By  the  use 
of  these  dynamos  it  is  possible  to  take  from  the  machine  volt- 
ages of  two  different  strengths  at  the  same  time,  the  higher 
voltage  being  double  that  of  the  lower,  and  thus  provide  a 
high  pressure  for  mechanical  plating  apparatus,  basket  work 
or  agitated  solutions,  and  at  the  same  time  operate  solutions 
of  a  low  voltage. 

In  wiring  for  this  system,  three  main  line  conductors  are 
used,  the  positive  and  negative,  or  outside  lines,  and  the 
neutral  or  middle  line.  In  this  method  of  wiring  there  is  a 
saving  of  over  37  per  cent,  effected  in  the  cost  of  copper,  as  it 
is  not  necessary  to  use  conductors  of  so  large  a  cross-section  as 
would  be  the  case  in  the  ordinary  two-wire  system. 

Figs.  68a  and  68b  illustrate  a  three-wire  system  showing 
plating  room  wired  for  the  usual  plating  tanks,  and  also 
mechanical  plating  apparatus.  All  necessary  voltmeters,  am- 
meters and  rheostats  are  shown. 

Suritch-boards.  In  the  sketch,  Fig.  66,  the  resistance-board 
belonging  to  each  bath  is  secured  to  the  wall  in  the  immediate 
neighborhood  of  the  bath.  This  arrangement  has  the  advan- 


ELECTRO-PLATING    ESTABLISHMENTS. 


181 


tage  that  the  operator  can,  directly  after  suspending  the  objects, 
conveniently    effect    regulation    from    the   bath    itself.      The 


182 


ELECTRO-DEPOSITION    OF    METALS. 


resistances  and  measuring  instruments,  as  well  as  the  switches, 
may,  however,  be  also  arranged  alongside  each  other  on  a 
switch-board.  Where  a  large  number  of  baths  are  in  opera- 


)u  u 

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^                                                                         ^r 

i. 

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I 

I 

j 

g 

tion,  several  such  switch-boards  will,  of  course,  have  to  be 
provided  to  avoid  the  necessity  of  the  operator,  having  to  walk 
too  great  a  distance  from  the  bath  to  the  switch-board. 


ELECTRO-PLATING    ESTABLISHMENTS. 


183 


Fig.  69  shows  such  a  switch-board,  upon  which  are  mounted 
the  dynamo  resistance,  the  resistance  for  the  accumulator,  two 
resistances  for  two  baths,  three  amperemeters,  a  voltmeter  with 
switch,  current  indicator,  as  well  as  switches  for  engaging  and 
disengaging  the  machine  as  well  as  the  accumulator.  For  the 
sake  of  neatness  the  conductors  and  connections  are  on  the 
back  of  the  switch-board. 

A  marble  slab  with  a  wood  rim  is  the  best  material  for  a 
switch-board.  Marble  or  slate  is  absolutely  required  if  the 
arrangements  for  starting  the  electro-motors  of  the  aggregates 

FIG.  69. 


or  transformers  are  mounted  upon  the  switch-board.  If,  in 
such  a  case,  the  latter  were  of  wood,  there  would  be  danger  of 
ignition  by  reason  of  the  heating  of  the  spirals,  etc.  Wooden 
switch-boards  may,  however,  be  used  for  measuring  instru- 
ment and  resistances  not  especially  subject  to  heating. 

The  suggestions  and  directions  given  in  the  section  "  In- 
stallation with  Cells  "  as  regards  regulation  of  current,  meas- 
uring instruments,  conductors,  tanks  for  solutions,  etc.,  apply 
also  to  installations  with  dynamos,  and  the  reader  is  referred 
to  that  section. 


184  ELECTRO-DEPOSITION    OK    METALS. 

C.  INSTALLATIONS  AND  ACCUMULATORS. 

Only  in  rare  cases  will  an  electro-plating  plant  be  operated 
by  an  accumulator  alone. 

For  larger  establishments,  where  deposits  requiring  many 
hours  for  finishing  are  made,  for  instance,  in  copper  and  nickel 
galvanoplasty,  silvering  by  weight,  etc.,  the  use  of  an  accumu- 
lator, in  addition  to  a  dynamo,  is  of  great  advantage,  since  the 
process  of  depositing  need  not  be  interrupted  during  the  noon 
intermission  or,  in  case  it  is  not  finished  in  the  evening,  dur- 
ing the  night,  such  interruptions  affecting  in  various  ways  the 
quality  of  the  deposit. 

However,  even  for  depositing  processes  requiring  a  shorter 
time,  for  instance  nickeling,  an  accumulator  gives  the  oppor- 
tunity of  turning  the  working  power  to  better  advantage. 
Suppose,  for  instance,  that  bicycle  parts  which  are  to  be 
solidly  nickeled  have  to  remain  in  the  bath  for  1J  hours. 
However,  the  steam  engine,  and  consequently  the  dynamo, 
are  stopped  at  12  M.  (noon),  and  hence  no  objects  can  be 
brought  into  the  bath  after  10:30  a.  m.,  as  otherwise  they 
would  not  be  finished  by  noon,  and  an  interruption  in  the 
nickeling  process  has  to  be  avoided.  If,  however,  an  accumu- 
lator can  during  the  noon  hour  be  used  for  feeding  the  baths, 
objects  can  be  suspended  up  to  that  time  in  the  baths  and 
taken  from  them  finished  when  the  noon-hour  expires  and 
operations  are  recommenced.  The  same  can  be  done  in  the 
evening,  and  thus  by  the  use  of  an  accumulator  the  producing 
power  of  an  electro-plating  plant  can  be  materially  increased. 

If  an  accumulator  is  thus  to  be  made  use  of,  a  dynamo  of  an 
adequately  larger  size  has  to  be  selected  so  that  in  addition  to 
the  depositing  work,  the  accumulator  can  at  the  same  time  be 
charged  by  direct  current  from  the  dynamo. 

In  establishments  where  the  current  is  generated  by  a  motor- 
generator  or  transformer  fed  from  a  central  station,  an  accumu- 
lator is  a  good  investment,  since  in  this  case  the  operating 
current  is  constantly  at  disposal  and  the  motor-generators  .and 
ransformers  can  consequently  run  day  and  night. 


ELECTRO-PLATING    ESTABLISHMENTS.  185 

Instead  of  feeding  the  baths  and  the  accumulator  simultane- 
ously with  current  from  a  larger  dynamo,  two  dynamos  may, 
of  course,  also  be  used,  one  of  them  supplying  the  baths  and 
the  other  the  accumulator. 

The  magnitude  of  the  performance  of  an  accumulator  de- 
pends on  the  current-strength  which  it  is  to  yield  for  a  certain 
time.  As  previously  stated,  the  value  ampere-strength  X  hours 
is  called  the  ampere-hour  capacity  of  an  accumulator.  Hence 
the  question  arises  for  how  long  the  accumulator  is  to  do  the 
work  of  the  dynamo  while  the  latter  is  not  running,  and  what 
-current-strength  is  during  this  time  to  be  transmitted  from  the 
accumulator  to  the  bath.  If  now  this  ampere-hour  capacity  is 
known,  as  well  as  the  maximum  current-strength  required  for 
feeding  the  bath  from  the  dynamo,  we  also  kntfw  the  current- 
strength  which  the  dynamo  must  have. 

To  explain  this  by  an  example,  we  will  suppose  that  the  bath 
requires  at  a  maximum  200  amperes,  and  that  the  dynamo  has 
to  directly  feed  the  bath  for  four  hours  and  at  the  same  time 
charge  a  cell,  which,  when  the  dynamo  stops,  is  to  discharge 
for  two  hours  with  200  amperes  to  the  bath.  The  cell  must 
therefore  have  a  capacity  of  400  ampere-hours,  and  taking  into 
•consideration  the  fact  that  for  charging  at  least  10  per  cent. 
more  charging  current  is  necessary  than  corresponds  to  the 
discharging  current,  440  amperes  will  have  to  be  used  for  one 
hour  in  order  to  charge  the  cell,  or  220  amperes  for  two  hours, 
140  amperes  for  four  hours.  Since  the  dynamo,  previous  to 
being  stopped,  has  directly  to  yield  for  four  hours  to  the  bath, 
200  amperes,  there  are  four  hours  at  disposal  for  charging 
the  cell,  and  the  dynamo  must  therefore  have  a  capacity  of 
200  +  110  ==  310  amperes. 

The  diagram  Fig.  69  shows  the  connection  of  a  plant  as 
installed  by  the  Electro-Chemical  Storage  Battery  Co.,  of  New 
York. 

By  suitable  manipulation  of  the  switches  and  rheostats  it  is 
possible  to  make  the  following  connections :  1.  The  dynamo 
alone  can  be  used  on  the  baths.  2.  The  batteries  alone  can 


186 


ELECTRO-DEPOSITION    OF    METALS. 
FIG.  70. 


ELECTRO-PLATING    ESTABLISHMENTS.  187 

be  used  on  the  baths.  3.  The  dynamo  can  be  used  on  the 
baths  and  the  batteries  charged  with  the  excess-current,  while 
at  the  same  time  steadying  the  dynamo  current.  4.  The 
dynamo  and  batteries  can  be  used  in  multiple  on  the  bathsr 
giving  a  greatly  increased  capacity. 


CHAPTER  V. 

PREPARATION    OF    THE    METALLIC    OBJECTS. 

As  previously  stated,  the  metallic  objects  to  be  plated  have 
to  undergo  both  a  mechanical  and  chemical  preparation,  and 
each  of  these  processes  will  be  considered  separately. 

A.     MECHANICAL  TREATMENT  PREVIOUS  TO  ELECTRO-PLATING. 

If  the  objects  are  not  to  be  plated  while  in  a  crude  state, 
which  is  but  rarely  feasible,  the  mechanical  treatment  consists 
in  imparting  to  them  a  cleaner  surface  by  scratch-brushing,  or  a 
smoother  and  more  lustrous  one  by  grinding  and  polishing.  It 
may  here  be  explicitly  stated  that  scratch -brushing  of  plated 
objects  is  not  to  be  considered  a  part  of  their  preparation, 
since  such  scratch-brushing  is  executed  in  the  midst  of,  or  after 
the  plating  process,  its  object  being  to  effect  an  alteration  of 
the  electro-deposits  in  more  than  one  direction,  and  not  the 
cleansing  of  the  surface  of  the  metallic  base.  The  following 
directions,  therefore,  apply  only  to  scratch-brushing  of  objects 
not  yet  plated.  The  scratch-brushing  of  electro-deposits  will 
be  considered  later  on.  In  regard  to  grinding,  we  have  to  deal 
with  the  subject  only  in  so  far  as  it  relates  to  smoothing  rough 
surfaces  by  the  use  of  grinding  powders  possessing  greater 
hardness  than  the  metal  to  be  ground.  With  grinding  in  the 
sense  of  instrument-grinding,  the  primary  object  of  which  is  to 
provide  the  instrument  with  a  cutting  edge,  we  have  nothing 
to  do. 

As  some  platers  seem  to  have  wrong  ideas  regarding  the 
electro-plating  process,  it  may  here  be  mentioned  that  the  de- 
posit is  formed  exactly  in  correspondence  with  the  surface  of 
the  basis-metal.  If  the  latter  has  been  made  perfectly  smooth 

(188) 


PREPARATION    OF    THE    METALLIC    OBJECTS.  189" 

by  grinding  and  polishing,  the  deposit  will  be  of  the  same 
nature;  but  if  the  basis-surface  is  rough,  the  deposit  also  will 
be  rough.  Hence  it  is  wrong  to  suppose  that  by  electro-plat- 
ing a  rough  surface  can  be  converted  into  a  lustrous  one,  and 
that  pores,  holes  or  scratches  in  the  basis-metal  can  be  filled 
by  plating.  In  order  to  obtain  a  deposit  which  is  to  acquire 
high  luster  by  polishing,  it  is  absolutely  necessary  to  bring 
the  basis  into  a  polished  state  by  mechanical  treatment.  In 
doing  this  it  is  not  necessary  to  go  so  far  as  to  produce  high 

FIG.  71.  FIG.  72.  FIG.  73.  FIG.  74. 


luster,  but  fine  scratches,  which  would  be  an  impediment  to  . 
attaining  high  luster  after  plating,  must  be  removed. 

Scratch-brushing  may  be  effected  either  by  hand  or  by  a 
scratch-brush  lathe.  For  hand-work,  scratch-brushes  of  more 
or  less  hard  brass  or  steel  wire,  according  to  the  hardness  of 
the  metal  to  be  manipulated,  are  used.  Various  forms  of 
brushes  are  employed,  the  most  common  ones  being  shown  in 
the  accompanying  illustrations  (Figs.  71  to  79). 

Fig.  78  shows  a  swing  brush  for  frosting  or  satin  finish,  and 


190 


ELECTRO-DEPOSITION    OF    METALS. 


Fig.  79  a  goblet  brush  without  stem  of  bristle  and  wire  for 
use  on  inside  of  goblets,  pitchers,  urns,  hollow  ware,  etc. 

In  scratch-brushing  it  is  recommended  first  to  remove,  or  at 
least  to  soften,  the  uppermost  hard  and  dirty  crust  (the  scale) 
by  immersing  the  objects  in  a  pickle,  the  nature  of  which 
depends  on  the  variety  of  metal,  so  that  a  complete  removal  of 
all  impurities  and  non-metallic  substances  may  be  effected  by 
means  of  the  scratch-brush  in  conjunction  with  sand,  pumice- 
.stone,  powder,  or  emery.  The  composition  of  pickles  will  be 


FIG.  75. 


FIG.  76. 


FIG.  7 


FIG  78. 


FIG  79. 


given  later  on.  Scratch-brushing  is  complete  only  when  the 
article  shows  a  clean  metallic  surface,  otherwise  the  brushing 
(scouring)  must  be  continued.  Scratch-brushes  must  be  care- 
fully handled  and  looked  after,  and  their  wires  kept  in  good 
order.  When  they  become  bent  they  have  to  be  straightened, 
which  is  most  readily  effected  by  several  times  drawing  the 
brush,  held  in  a  slanting  position,  over  a  sharp  grater  such  as 
is  used  in  the  kitchen.  By  this  means  the  wires  become  dis- 
entangled and  straightened  out. 


PREPARATION    OF    THE    METALLIC    OBJECTS.  191 

Hand  scratch-brushing  being  slow  and  tedious  work,  large 
•establishments  use  circular  scratch-brushes  which  are  attached 
to  the  spindle  of  a  lathe.  These  circular  brushes  consist  of 
round  wooden  cases  in  which,  according  to  requirement,  1  to 
6  or  more  rows  of  wire  bundles  (see  Fig.  80)  are  inserted. 

Brushes  with  wooden  cases  are,  however,  more  suitable  for 
scratch-brushing  deposits  than  for  cleansing  the  metallic  base, 
since  for  the  latter  purpose  a  more  energetic  pressure  is  usually 
.applied,  in  consequence  of  which  the  bundles  bend  and  even 
break  off,  if  the  wire  is  anyways  brittle.  For  cleansing  pur- 
poses a  circular  scratch-brush,  which  the  workman  can  readily 
refurnish  with  new  bundles  of  wire,  deserves  the  preference. 
It  is  constructed  as  follows  :  A  round  iron  disk  about  0.11  inch 
thick,  and  from  5f  to  7}  inches  in  diameter,  is  provided  in 

FIG.  80. 


the  center  with  a  hole  so  that  it  can  be  conveniently  placed 
upon  the  spindle  of  the  lathe.  At  a  distance  of  from  0.19  to 
0.31  inch  from  the  periphery  of  the  disk,  holes  0.079  to  0.11 
inch  in  diameter  are  drilled,  so  that  between  each  two  holes 
is  a  distance  of  0.15  inch.  Draw  through  these  holes  bundles 
of  wire  about  3.93  inches  long,  so  that  they  project  an  equal 
distance  on  both  sides.  Then  bend  the  bundles  towards  the 
periphery,  and  on  each  side  of  the  iron  disk  place  a  wooden 
disk  0.31  to  0.39  inch  thick.  The  periphery  of  the  wooden 
disk,  on  the  side  next  to  the  iron  disk,  should  be  turned  semi- 
annular,  so  that  the  wooden  disks  when  secured  to  the  spindle 
press  very  lightly  upon  the  wire  bundles,  and  the  latter  re- 
main very  mobile.  When  a  circular  scratch-brush  constructed 


192  ELECTRO-DEPOSITION    OF    METALS. 

in  this  manner  and  secured  to  the  lathe  is  allowed  to  make 
from  1800  to  2000  revolutions  per  minute,  the  bundles  of  wire, 
in  consequence  of  the  centrifugal  force,  stand  very  rigid,  but 
being  mobile  will  give  way  under  too  strong  a  pressure  with- 
out breaking  off,  and  can  thus  be  utilized  to  the  utmost. 
When  required,  the  iron  disk  can  be  refurnished  with  wires  in 
less  than  half  an  hour.  An  error  frequently  committed  is  that 
the  objects  to  be  cleansed  are  pressed  with  too  heavy  a  pres- 
sure against  the  wire  brushes.  This  is  useless,  since  only  the 
sharp  points  of  the  wire  are  effective,  the  lateral  surfaces  of  the 
bundles  removing  next  to  nothing  from  the  articles. 

Brushes.  A  definition  of  these  instruments  is  unnecessary, 
and  we  shall  simply  indicate  the  various  kinds  suitable  to  the 
different  operations. 

The  fire-gilder  employs,  for  equalizing  the  coating  of  amal- 

FIG.  81.  FIG.  82.  FIG.  83. 


gam,  a  long-handled  brush,  the  bristles  of  which  are  long  and 
very  stiff".  The  electro-gilder  uses  a  brush  (Fig.  81)  with  long 
and  flexible  bristles. 

For  scouring  with  sand  and  pumice-stone  alloys  containing 
nickel,  such  as  German  silver,  which  are  difficult  to  cleanse  in 
acids,  the  preceding  brush,  with  smaller  and  stiffer  bristles,  is 
used. 

The  gilder  of  watch-works  has  an  oval  brush  (Fig.  82),  with 
stiff  and  short  bristles  for  graining  the  silver. 

The  galvanoplastic  operator,  for  coating  moulds  with  black- 
lead,  besides  a  number  of  pencils,  uses  also  three  kinds  of 
brushes — the  watchmaker's  (Fig.  83),  a  hat  brush,  and  a 
blacking-brush.  The  bronzer  uses  all  kinds  of  brushes. 

Brushes  are  perfectly  freed  from  adherent  grease  by  washing 
with  benzine  or  carbon  disulphide. 


PREPARATION    OF    THE    METALLIC    OBJECTS. 


193 


In  large  establishments  engaged  in  electro-plating  cast-iron 
without  previous  grinding,  the  use  of  the  sand-blast,  in  place  of 
the  circular  wire  brush,  has  been  introduced  with  great  advan- 
tage. Objects  with  deep  depressions,  which  cannot  be  reached 
with  the  scratch-brush,  as  well  as  small  objects,  which  cannot 
be  conveniently  held  in  the  hand  and  pressed  against  the  re- 
volving scratch-brush,  can  be  brought  by  the  sand-blast  into  a 
state  of  sufficient  metallic  purity  for  the  electro-plating  process. 

However,  while  circular  scratch-brushes  impart  to  the  ob- 

FIG.  84. 


jects  a  certain,  though  not  very  great  luster,  the  metal  por- 
tions are  matted  by  the  sand-blast,  and  the  latter  is  frequently 
employed  for  matting  entire  lustrous  surfaces  or  for  produc- 
ing contrasts,  for  instance,  mat  designs  upon  lustrous  grounds, 
or  vice  versa. 

A  large  variety  of  types  of  sand-blasting  machines  have 
been  introduced,  a  number  of  them  having  been  designed  for 
use  in  cleansing  large  iron  castings  for  engineering  work.  A 
sand-blast  suitable  for  the  electro-plater's  purpose  is  shown  in 
Fig.  84.  It  is  very  compact  and  convenient  for  use  in  a 
14 


194  ELECTRO-DEPOSITION    OF    METALS. 

limited  floor  space.  The  necessary  pressure  is  obtained  by 
compressed  air.  The  compressed  air,  the  pressure  of  which 
should  be  at  least  equal  to  that  of  a  column  of  water  18J 
inches  high,  passes  through  the  blast-pipe  A  into  a  nozzle 
running  horizontally  through  the  machine,  carries  along  a 
jet  of  sand,  and  hurls  the  latter  upon  the  objects  placed  under- 
neath the  nozzle.  The  objects  are  placed  upon  sheet-iron 
plates  or  in  sheet-iron  boxes  and  very  slowly  passed  below  the 
nozzle,  the  motion  being  effected  by  the  shafts  BB  with  the 
use  of  rubber  belts.  To  avoid  dust,  the  machine  is  provided 
with  a  jacket  of  sheet-iron  or  wood  ;  a  few  windows  enable  the 
operator  to  watch  the  progress  of  the  operation. 

The  uses  to  which  a  sand-blast  can  be  put  are  very  numer- 

FIG.  85. 


ous.  The  frosting  or  satin-finishing  of  silverware  and  other 
articles,  engraving  or  stenciling  of  metal  or  glass,  inlaying, 
removing  scale,  etc.,  the  nature  of  the  work  being  governed 
by  the  fineness  of  the  sand  used  as  well  as  the  pressure. 

If  a  clean  metallic  surface  is  at  one  time  to  be  given  to  a 
large  number  of  small  articles,  such  as  buckles,  steel  beads, 
metal  buttons,  steel  watch  chains,  ferrules,  etc.,  a  tumbling 
barrel  or  drum  is  frequently  used  (Fig.  85).  It  generally  con- 
sists of  a  cylindrical  or  polygonal  box  having  a  side  door  for 
the  introduction  of  the  work,  together  with  sharp  sand  or 
emery,  and  is  mounted  horizontally  on  an  axis  furnished  with 
a  winch  or  pulley,  so  as  to  be  revolved  either  by  hand  or 
power,  as  may  be  desired.  In  order  to  prevent' certain  objects, 


PREPARATION    OF    THE    METALLIC    OBJECTS.  195 

like  hooks  for  ladies'  dresses  and  the  like,  from  catching  each 
other  and  combining  into  a  mass,  a  number  of  nails  or 
wooden  pegs  are  fixed  in  the  interior  of  the  drum. 

For  ordinary  polishing  -the  articles  are  brought  into  the 
tumbling  barrel  together  with  small  pieces  of  leather  waste 
(leather  shavings),  arid  taken  out  in  one  or  two  days.  How- 
ever, to  produce  an  actually  good  polish  a  somewhat  more 
complicated  method  has  to  be  pursued.  The  articles  are  first 
freed  from  adhering  scale  by  washing  in  water  containing  5 
per  cent,  of  sulphuric  acid,  then  rinsed  and  dried  in  a  drying 
chamber,  or  in  a  pan  over  a  fire.  They  are  next  brought  into 
the  tumbling  barrel  together  with  sharp  sand,  such  as  is  used  in 
glass-making,  and  revolved  for  about  12  hours,  when  they  are 
taken  from  the  barrel  and  freed  from  the  admixed  sand  by  sift- 
ing. They  are  then  returned  to  the  barrel,  together  with  soft, 
fibrous  sawdust,  to  free  them  from  adhering  sand,  and  at  the 
same  time  to  give  them  a  smoother  surface.  They  are  now 
again  taken  from  the  barrel,  freed  from  sawdust,  and  returned 
to  the  barrel,  together  with  leather  shavings.  They  now  re- 
main in  the  barrel  until  they  have  acquired  the  desired  polish, 
which,  according  to  the  size  and  shape  of  the  articles  and  the 
degree  of  polish  required,  may  frequently  take  two  weeks  or 
more.  Articles  of  different  shapes  and  sizes  are  best  treated 
together,  time  being  thereby  saved.  The  process  is  also  accel- 
erated by  adding  some  fat  oil  to  the  leather  shavings,  which, 
of  course,  must  be  omitted  when,  after  long  use,  the  shavings 
have  become  quite  greasy.  The  barrel  should  be  filled  about 
half  full,  otherwise  the  articles  do  not  roll  freely,  and  polish- 
ing is  retarded.  On  the  other  hand,  when  the  barrel  is  less 
than  half  full  there  is  danger  of  the  articles  bending,  or  in 
case  they  are  hardened,  for  instance  buckles,  of  breaking. 

For  many  purposes  polishing  in  the  tumbling  barrel  is  of 
great  advantage,  since,  independent  of  its  cheapness,  the  sharp 
edges  of  the  articles  are  at  the  same  time  rounded  off.  How- 
ever, with  articles  the  edges  of  which  have  to  remain  sharp, 
the  process  cannot  be  employed. 


196 


ELECTRO-DEPOSITION    OF    METALS. 


FIG.  86. 


The  tumbling  barrel  in  which  the  articles  are  treated  with 
sand  cannot  be  used  for  polishing  with  leather  shavings,  it 
being  next  to  impossible  to  free  it  entirely  from  sand.  The 
barrels  should  make  from  50  to  76  revolutions  per  minute;  if 
allowed  to  revolve  more  rapidly,  the  articles  take  part  in  the 
revolutions  without  rolling  together,  which,  of  course,  would 
prevent  polishing. 

The  brightening  of  articles  of  iron  and  steel  may  be  simpli- 
fied by  using  water  to  which  1  per  cent,  of  sulphuric  acid  has 
been  added.  The  barrel  used  for  the  purpose  must,  of  course, 
be  water-tight.  By  the  addition  of  sand  the  process  is  acceler- 
ated. Nickel  and  copper  blanks  for  coins  are  also  cleansed  in 
this  manner.  They  are  brought  into  the  tumbling  barrel, 
together  with  a  pickling  fluid,  and,  when  sufficiently  treated, 
are  taken  out,  rinsed,  dried  in  sawdust,  and  finally  stamped. 
Fig.  86  sho'ws  a  form  of  an  adjustable,  oblique  tumbling 

barrel,  adapted  to  clean,  smooth 
brighten,  and  polish  nearly  every 
variety  of  iron  and  brass  goods.  The 
simplicity  and  durability  of  the  con- 
struction and  the  rapidity  with  which 
the  work  is  done  are  distinct  advan- 
tages. The  machine  can  be  used 
wet  or  dry.  It  is  adjustable  by  screw 
and  wheel  to  any  working  elevation 
up  to  50°.  The  machine  shown  in 
the  illustration  is  designed  to  carry 
a  barrel  24  inches  in  diameter,  but 
larger  or  smaller  barrels  can  be  used. 
Grinding.  Wooden  wheels  cov- 
ered with  leather  coated  with  emery  of  various  degrees  of  fine- 
ness are  almost  exclusively  used  for  grinding  metallic  objects 
preparatory  to  the  plating  process.  The  wooden  wheels  are 
made  of  thoroughly-seasoned  poplar,  in  the  manner  shown 
in  Fig.  87.  The  separate  pieces  are  radially  glued  together, 
and  upon  each  side  in  the  center  a  strengthening  piece  is 


PREPARATION  OF    THE    METALLIC    OBJECTS.  197 

glued  and  secured  with  screws,  so  that  each  segment  of  the 
wheel  is  connected  with  the  strengthening  piece.  The  center 
of  the  wheel  is  then  provided  with  a 
hole  corresponding  to  the  diameter  of  the 
spindle  of  the  grinding  lathe,  to  which  it 
is  secured  by  means  of  wedges.  The 
periphery,  as  well  as  the  sides,  is  then 
turned  smooth.  A  good  quality  of 
leather,  previously  soaked  in  water  and 
cut  into  strips  corresponding  to  the  width 
of  the  wheel  is  then  glued  to  the  periph- 
ery, and  still  further  secured  by  pins  of  soft  wood.  '  When  the 
glue  is  dry  the  wheel  is  again  wedged  upon  the  spindle  and 
the  leather  case  fully  turned;  it  is  then  ready  for  coating  with 
emery. 

With  the  use  of  grinding  wheels  of  oak  or  walnut,  covering 
with  leather  may  be  omitted,  and  the  emery  can  be  applied 
directly  to  the  wheels.  However,  leather-covered  wheels  are 
to  be  preferred  since,  by  reason  of  their  elasticity,  better  results 
in  grinding  are  obtained  than  with  uncovered  wheels  of  the 
above-mentioned  varieties  of  wood. 

For  grinding  soft  metals,  hard,  impregnated  felt  wheels 
"  set  up  "  with  glue  and  emery  are  also  employed. 

For  grinding  profiled  articles  preference  should  be  given  to 
wheels  without  leather  covering,  and  the  grinding  surface 
should  be  fitted  to  the  profile  of  the  article  to  be  ground  by 
cutting  with  a  turning  tool. 

Grinding  wheels  of  paste-board  and  of  cork  waste  have  re- 
cently been  introduced.  The  former  are  made  by  coating  on 
both  sides  thin,  round  disks  of  paste-board  with  glue  mixed 
with  emery,  and  then  gluing  a  sufficient  number  of  such 
disks  one  upon  the  other  to  form  a  wheel  of  the  desired  width. 
The  wheel  is  finally  subjected  to  strong  pressure  under  a 
hydraulic  press,  and  dried.  However,  as  these  wheels  have 
disappeared  from  commerce,  it  may  be  assumed  that  they 
have  not  stood  the  test  in  practice.  The  same  may  be  said  of 


198 


ELECTRO-DEPOSITION    OF    METALS. 


FIG.  88. 


cork  wheels.  The  so-called  elastic  wheel  has  also  not  an- 
swered the  demands  made  in  practice.  The  cementing  mater- 
ial in  the  case  consisted  of  a  gum  or 
rubber-like  mass,  which  to  be  sure 
imparted  great  elasticity  to  the 
wheel,  but  when  the  latter  became 
hot  during  grinding,  the  mass  soft- 
ened and  smeared. 

The  so-called  reform  wheel,  Fig. 
88,  has  a  better  prospect  of  general 
introduction..  The  leather  covering 
does  not  consist  of  a  single  strap,  but 
pieces  of  leather,  3  to  5  millimeters 
thick,  are  placed  alongside  each  other 
and  secured  by  means  of  a  sort  of 
dove-tailing  to  an  iron  rim,  which 

is  screwed  upon  the  wooden  disk.  According  to  the  length 
of  the  pieces  of  leather  a  greater  or  smaller  degree  of  elasticity 
is  attained.  One  covering  lasts  at  least  five  to  eight  times 
as  long  as  the  covering  with  leather  straps,  and  leather-waste, 
otherwise  of  scarcely  any  value,  may  be  employed  for  the 
covering. 

For  grinding  soft  metals,  hard  impregnated  felt  wheels 
coated  by  means  of  glue  with  emery  are  also  used. 

For  gluing  with  emery  three  different  kinds  of  emery  are 
used,  a  coarse  quality  (Nos.  60  to  80)  for  preparatory  grind- 
ing, a  finer  quality  (No.  00)  for  fine  grinding,  and  the  finest 
quality  (No.  0000)  for  imparting  luster.  The  wheels  thus 
coated  are  termed  respectively  "  roughing  wheel,"  "medium 
wheel,"  and  "fine  wheel."  With  the  first  the  surface  of  the 
objects  are  freed  from  the  rough  crust.  The  coarse-grained 
emery  used  for  this  purpose,  however,  leaves  scratches,  which 
have  to  be  removed  by  grinding  upon  the  medium  wheel  until 
the  surfaces  of  the  objects  show  only  the  marks  due  to  the 
finer  quality  of  emery,  which  are  in  their  turn  removed  by 
the  fine  wheel. 


PREPARATION    OF    THE    METALLIC    OBJECTS. 

In  most  cases  brushing  with  a  circular  bristle  brush  may  be 
substituted  for  the  last  grinding,  the  articles  being  moistened 
with  a  mixture  of  oil  and  emery  No.  0000.  Care  must  be  had 
not  to  execute  the  brushing  nor  the  grinding  with  the  finer 
quality  of  emery  in  the  same  direction  as  the  preceding  grind- 
ing, but  in  a  right  angle  to  it. 

Treatment  of  the  grinding  wheels. — The  coating  of  the  rough- 
ing wheels  with  emery  is  effected  by  applying  to  them  a 
good  quality  of  glue  and  rolling  them  in  dry,  coarse  emery 
powder.  For  the  medium  and  fine  wheels,  however,  the  emery 
is  mixed  with  the  glue  and  the  mixture  applied  to  the  leather. 
When  the  first  coat  is  dry,  a  second  is  applied,  and  finally  a 
third.  The  whole  is  then  thoroughly  dried  in  a  warm  place. 
Before  use,  a  piece  of  tallow  is  held  to  the  revolving  disc  for 
the  purpose  of  imparting  a  certain  greasiness  to  it,  and  in  order 
to  remove  any  roughness  due  to  an  unequal  application  of  the 
emery,  it  is  smoothed  by  pressing  a  smooth  stone  against  it. 
While  the  preparatory  grinding  upon  the  roughing  wheel  is 
executed  dry,  i.  e.,  without  the  use  of  oil  or  fat,  in  fine  grinding, 
the  objects  are  frequently  moistened  with  a  mixture  of  oil  and 
the  corresponding  No.  of  emery.  When  the  layer  of  emery  is 
used  up,  the  remainder  is  soaked  with  warm  water  and  scraped 
off  with  a  dull  knife.  The  leather  of  the  disks  on  which  oil  or 
tallow  has  been  used  is  then  thoroughly  rubbed  with  caustic 
lime  or  Vienna  lime  *  to  remove  the  greasiness,  which  would 
prevent  the  adherence  of  the  layer  of  glue  and  emery  to  be 
applied  later  on.  When  the  leather  is  thoroughly  dry  a  fresh 
layer  of  emery  may  at  once  be  applied. 

To  prevent  the  leather  from  absorbing  an  excess  of  water 
when  moistening  the  old  layer  of  glue  and  emery  for  the  pur- 
pose of  softening  it,  it  is  advisable  to  apply  moderately  wet 
i 

*  Vienna  lime  is  prepared  from  a  variety  of  dolomite  which  is  first  burned,  then 
slaked,  and  finally  ignited  for  a  few  hours.  It  consists  of  lime  and  magnesia,  and 
should  be  kept  in  well-closed  cans,  as  otherwise  it  absorbs  carbonic  acid  and 
moisture  from  the  air,  and  becomes  useless. 


200  ELECTRO-DEPOSITION    OF    METALS. 

clay  to  the  layer  and  allow  it  to  remain  for  a  few  hours  when 
the  emery  can  be  readily  scraped  off. 

A  very  useful  machine  for  removing  emery  and  glue  from 
worn,  leather-covered  wood  polishing  wheels  is  shown  in  Fig. 
89.  The  compartment  is  filled  with  water  until  it  just  touches 
the  lower  part  of  the  rollers.  Then  by  placing  the  worn 
wheels  on  the  rollers  and  allowing  the  machine  to  run  for  a 
short  time  all  the  glue  and  emery  will  be  removed  without 
damaging  or  loosening  the  leather  covering.  The  rollers 
carry  just  enough  water  to  properly  feed  the  face  of  the  wheels, 
and  the  friction  caused  by  the  weight  of  the  wheels  revolving 

FIG.  89. 


on  the  rollers  quickly  forces  off  the  emery  and  glue.  Allow 
the  wheels  to  dry  in  the  ordinary  temperature  ;  do  not  subject 
them  to  heat. 

Grinding  lathes.  For  use,  the  grinding  wheels  are  wedged 
upon  a  conical  cast-steel  spindle  provided  with  a  pulley  and 
running  in  bearings,  as  plainly  shown  in  Fig.  90.  The  cast- 
iron  standards  are  screwed  to  the  floor ;  the  wooden  bearings 
can  be  shifted  forward  and  backward  by  wedges  and  secured 
in  a  determined  position  by  a  set-screw,  thus  facilitating  the 
removal  of  the  spindle  after  throwing  off  the  belt.  The 
wheels  being  wedged  upon  a  conical  spindle,  always  run 


PREPARATION    OF    THE    METALLIC    OBJECTS.  201 

•centrically.      Changing   of  the   wheels   requires   but   a   few 

FIG.  90. 


seconds,  and  on  account  of  the  slight  friction  of  the  points  of 

Fro.  91. 


the  spindle  in  the  wooden  bearings,  the  consumption  of  power 
is  very  slight. 


202 


ELECTRO-DEPOSITION    OF    METALS. 


To  avoid  the  necessity  of  throwing  off  the  belt  while  chang- 
ing the  grinding  wheels,  double  machines  (Fig.  91)  are  used, 
the  principle  of  conical  spindles  being,  however,  preserved. 
The  shaft  is  provided  with  loose  and  fast  pulley  and  coupling 
lever. 

Fig.  92  illustrates  a  similar  machine  with  ring-oiling. 

Fig.  93  represents  a  belt-attachment  combined  with  a  double 
grinding  lathe,  as  constructed  by  the  firm  of  Dr.  G.  Langbein 
&  Co.  The  apparatus  can  be  readily  secured  by  means  of 
screws  to  the  lathe,  and  is  readily  removed.  It  allows  of 


grinding- wheels,  brushes,  etc.,  being  attached  to  both  ends  of 
the  shaft,  while  the  belt  can  at  the  same  time  be  used. 

Electrically-driven  grinding  motors  have  been  previously  re- 
ferred to.  Fig.  94  shows  a  grinder  of  this  type  manufactured 
by  The  Hanson  &  Van  Winkle  Co.,  Newark,  N.  J.  It  is  of 
the  ribbed  type,  and  is  furnished  in  various  sizes.  The  switch, 
starting  box  and  regulator  are  contained  within  the  stand, 
with  the  operating  handles  extending  through  a  suitable  open- 
ing. An  important  feature  of  this  machine  is  the  ability  of 


PREPARATION    OF    THE    METALLIC    OBJECTS.  20S 

the  operator  to  regulate  the  speed  of  the  wheels,  running  them 
at  the  speeds  most  suitable  for  the  work  in  hand.  This  regu- 
lation of  the  speed  is  accomplished  by  the  simple  movement 
of  a  handle,  the  speed  remaining  practically  constant  at  any 
point. 

A  smaller  type  of  the  same  machine  is  very  suitable  for  use 
by  manufacturers,  jewelers,  dentists,  instrument  makers,  etc. 

FIG.  93. 


These  grinding  motors,  as  well  as  the  polishing  motors  to- 
be  described  later  on,  have  the  advantage  of  occupying  no 
more  space  than  that  is  usually  required  by  a  belt-driven 
lathe,  while  the  full  motive  power  is  applied,  without  loss, 
directly  to  the  grinding  wheels.  They  also  possess  the  ad- 
vantage of  being  portable,  and  in  a  few  moments'  time  can  be 


204  ELECTRO-DEPOSITION    OF    METALS. 

moved  to  any  part  of  the  factory  that  may  be  best  suited  for 
the  purpose  required,  making  it  possible  to  take  the  motor  to 
the  work  when  desired,  instead  of  bringing  the  work  to  the 
motor. 

Execution  of  grinding  and  brushing.  Grinding  is  executed 
by  pressing  the  surfaces  to  be  ground  against  the  face  of  the 
wheel,  moving  the  objects  constantly  to  and  fro.  The  opera- 
tion requires  a  certain  manual  skill,  since,  without  good 
reason,  no  more  should  be  ground  away  on  one  place  than  on 

FIG.  94. 


another.     Special  care  and  skill  are  required  for  grinding 
large  round  surfaces. 

If  the  objects  are  to  be  treated  with  the  fine  wheel,  fine 
grinding  is  succeeded  by  brushing  with  oil  and  emery  by 
means  of  circular  brushes  formed  of  bristles  set  in  disks  of 
wood.  Genuine  bristles  being  at  present  very  expensive, 
vegetable  fiber,  so-called  fibers,  has  been  successfully  substi- 
tuted for  them,  the  wooden  wheel  being  replaced  by  an  iron 
•case,  in  the  bell-shaped  cheeks  of  which  the  fiber-bundles  are 
•secured  by  means  of  strong  nuts.  Before  use  it  is  advisable  to 


PREPARATION    OF    THE    METALLIC    OBJECTS. 


205 


saturate  fhe  fiber-bundles  with  oil  in  order  to  deprive  them  of 
their  brittleness,  and  thus  improve  their  lasting  quality. 

The  grinding  lathe  (Fig.  95)  is  provided  with  a  tampico 
brush,  this  fiber  being  particularly  adapted  for  rough,  quick 
work.  It.  can,  of  course,  just  as  well  be  placed  upon  the  con- 
ical spindles  of  double  machines.  The  iron  case  is  provided 
with  a  conical  hole  corresponding  exactly  to  the  conical  spin- 
dle, the  large  frictional  surface  preventing  the  turning  of  the 
brush  upon  the  spindle,  or  its  running  off. 


FIG.  95. 


FIG.  96. 


In  regard  to  grinding  the  various  metals,  the  procedure, 
according  to  the  hardness  of  the  metal,  is  as  follows : 

Iron  and  steel  articles  are  first  ground  upon  the  roughing 
wheel,  then  fine-ground  upon  the  medium  wheel,  and  finally 
upon  the  fine  wheel,  or  brushed  with  emery  with  the  circular 
brush.  Very  rough  iron  surfaces  may  first  be  ground  upon 
solid  emery  wheels  before  being  worked  upon  the  roughing 
wheel. 

For  depressed  surfaces  which  cannot  be  reached  with  the 
large  emery  wheels,  small  walrus-hide  wheels  coated  with  glue 
and  emery  are  placed  upon  the  point  of  the  spindle  of  a 
polishing  lathe. 


206 


ELECTRO-DEPOSITION    OF    METALS. 


Brass  and  copper  castings  are  first  ground  upon  roughing 
wheels  which  have  lost  part  of  their  sharpness  and  will  no 
longer  attack  iron.  They  are  then  ground  fine  upon  the 
medium  wheel,  and  finally  polished  upon  cloth  or  felt  wheels 
(bobs).  (See  below  under  "Polishing.") 

Sheets  of  brass,  German  silver  and  copper,  as  furnished  by 
rolling-mills,  are  only  brushed  with  emery  and  then  polished 
with  Vienna  lime  or  rouge  upon  bobs. 

Zinc  castings,  as,  for  instance,  those  produced  in  lamp  fac- 
tories, are  first  thoroughly  brushed  by  means  of  circular 
brushes  and  emery,  and  then  polished  upon  cloth  bobs. 


FIG.  97. 


FIG. 


\ 


Sheet  zinc  is  only  polished  with  Vienna  lime  and  oil  upon 
cloth  bobs  secured  to  the  spindle  shown  in  Fig.  101. 

Polishing. — As  will  be  seen  from  the  foregoing,  polishing 
serves  for  making  the  articles  ready,  i.  e.,  the- final  luster  is 
imparted  to  them  upon  soft  polishing  wheels  with  the  use  of 
fine  polishing  powder.  The  polishing  wheels  or  bobs  of  fine 
felt,  shirting,  or  cloth,  are  secured  to  the  polishing  lathe,  and, 
according  to  the  hardness  of  the  metal  to  be  polished,  make 


PREPARATION    OP    THE    METALLIC    OBJECTS.  207 

2000  to  2500  revolutions  per  minute.  A  foot-lathe,  such  as  is 
shown  in  Fig.  96,  makes  generally  not  over  1800  revolutions 
per  minute.  Cloth  bobs  are  made  by  placing  pieces  of  cloth 
one  upon  another  in  the  manner  described  under  "  Nickeling 
of  sheet  zinc,"  cutting  out  the  center  so  as  to  correspond  to 
the  diameter  of  the  spindle,  and  securing  the  disks  of  cloth  by 
means  of  nuts  between  two  wooden  cheeks  upon  the  spindle  of 
the  polishing  lathe.  In  place  of  cloth  bobs,  solid  wheels  of 
felt  or  wooden  wheels  covered  with  a  layer  of  felt  may  be  used, 
especially  for  polishing  smooth  objects  without  depressions, 
the  fineness  and  softness  of  the  felt  depending  on  the  degree 
of  polish  to  be  imparted  and  the  hardness  of  the  metal  to  be 
manipulated. 

An  excellent  polishing-wheel  is  the  Union  canvas  wheel, 
made  by  the  Hanson  &  Van  Winkle  Co.,  of  Newark,  N.  J. 
It  is  shown  in  Fig.  97.  It  is  not  glued,  but  by  a  special 
process  the  weight  is  reduced,  the  elasticity  and  flexibility  are 
increased,  and  a  cloth  face  is  obtained,  which  combined  with 
the  glue,  presents  a  surface  that  will  hold  emery  better  than 
any  other  wheel.  Being  of  a  flexible  nature,  it  easily  adjusts 
itself  to  the  irregularities  of  the  work.  No  special  skill  is  re- 
quired to  use  it,  and  there  is  less  tendency  to  "  gouge  "  the 
work  or  spoil  design.  The  wheel  will  do  more  work  with  one 
setting-up  than  any  other.  It  is  durable  and  easily  kept  in 
balance. 

Fig.  98  shows  the  universal  polishing  wheel  made  by  the 
Hanson  &  Van  Winkle  Co.  This  wheel  is  superior  in  every 
way.  It  is  practically  universal  and  decidedly  economical. 
It  can  be  used  for  "  roughing,"  "  fining  ",  or  "  greasing."  It 
retains  its  shape — does  not  rag  out,  and  will  stay  in  balance 
almost  indefinitely.  It  is  resilient  and  remains  so  until  nearly 
worn  out.  A  finer  grade  of  emery  can  be  used,  and  the 
emery  can  be  washed  off  and  a  new  face,  fine,  smooth,  and 
glazed,  can  be  obtained  for  another  setting  up.  The  wheel 
will  not  burn  the  surface  of  the  metal  and  in  consequence  a 
better  "  color"  after  plating  is  obtained.  It  is  made  in  three 
grades;  soft,  medium  and  hard. 


208  ELECTRO-DEPOSITION    OF    METALS. 

Another  wheel  of  great  flexibility  and  elasticity  is  the  wal- 
rine  wheel  manufactured  by  the  same  firm.  On  account  of 
its  flexibility  and  elasticity,  combined  with  its  hardness,  it  is 
recommended  for  hard  grinding,  and  the  fact  that  its  face  can 
be  turned  to  any  shape — at  the  same  time  preserving  all  the 
characteristics  of  hide  wheels — will  place  it  before  sea-horse 
or  walrus  on  its  merits.  One  advantage  of  this  wheel  is  its 
pliability,  which  allows  it  to  adjust  itself  to  any  inequalities 
in  the  coat  of  emery,  and  consequently  it  wears  evenly,  and 
being  lighter  than  any  other  serviceable  wheel,  it  is  much  less 
liable  to  injure  lathe  bearings. 

Double  polishing  lathes  according  to  American  patterns, 
Figs.  99  and  100,  are  used  for  polishing  objects  of  not  too 
large  dimensions.  These  polishing  lathes  are  manufactured 

FIG.  99. 


in  several  sizes,  the  largest  capable  of  using  wheels  15  inches 
diameter  and  5  inches  face.  Fig.  99  shows  a  10-inch  polish- 
ing head  to  be  screwed  to  a  bench. 

Fig.  100  illustrates  a  14-inch  ring-oiling  polishing  machine. 
The  head  is  constructed  so  as  to  give  plenty  of  room  between 
the  wheels  and  the  column,  thus  making  the  machine  of 
special  advantage  where  awkward  pieces  are  to  be  handled,  as 
bicycle,  chandelier,  and  similar  classes  of  work.  The  bear- 
ings provided  are  peculiar  to  the  machine,  the  boxes  being  so 
constructed  that  the  spindle  has  four  bearings,  thus  affording 
a  good  support  and  making  the  machine  a  stiff  and  durable 
one. 


PREPARATION    OF    THE    METALLIC    OBJECTS.  209 

The  polishing  lathe  shown  in  Fig.  101  serves  chiefly  for 

FIG.  100. 


polishing  large  sheets,  the  latter  being  placed  upon  a  smooth, 

Fro.  101. 


wooden  support  which  rests  upon  the  knees  of  the  workman, 
as  will  be  described  later  on  in  speaking  of  nickeling  sheet-zinc. 
14 


210 


ELECTRO-DEPOSITION    OF    METALS. 


Fig.  102  shows  an  independent  spindle-polishing  and  buff- 
ing lathe  manufactured  by  The  Hanson  &  Van  Winkle  Co., 
Newark,  N.  J.  In  designing  this  lathe  further  demands  for 
economy,  viz.,  power,  shafting  and  belting  have  been  antici- 
pated. Countershafts,  loose  pulleys  and  incidental  belting  are 
dispensed  with.  To  accomplish  this,  a  single  driving  pulley 
and  double  friction  cones,  securely  housed  in  the  lathe  head^ 
as  shown  in  the  illustration,  are  used  on  the  lathe. 

FIG.  102. 


The  forged  steel  clutches  are  operated  by  small  hand  levers 
above  the  casing.  A  study  of  the  illustration  will  show  the 
great  strength  and  large  provision  for  wear  in  the  double  fric- 
tion cones,  as  well  as  the  spindle  bearings,  and  the  means  for 
oiling. 

The  lathe  spindle  is  of  large  diameter,  carefully  ground  and 
polished ;  it  runs  smoothly  and  noiselessly  and  without  end 
play.  Throwing  off  the  clutch  brings  a  brake  into  action  and 


PREPARATION    OF    THE    METALLIC    OBJECTS.  211 

stops  the  spindle  instantly,  while  the  reverse  motion  releases 
the  brake  and  starts  the  spindle  immediately.  This  is  done 
at  either  end  without  interference  or  waiting ;  as  a  result  there 
is  no  lost  time  for  either  operator,  which  means  a  saving  of 
from  one  to  three  hours  per  day. 

The  pedestal  flares  at  the  back  so  that  the  latter  can  be 
belted  from  below,  a  method  now  used  in  many  shops,  and 
always  to  be  preferred,  as  it  gives  a  room  entirely  free  of  belts. 

Electrically-driven  polishing  and  buffing  lathes  are  now  in 
frequent  use.  The  high  speed  at  which  emery  and  polishing 

FIG.  103. 


wheels  are  run  necessitates  tight  belts,  heated  bearings,  and  the 
dirt  carried  by  the  belt.  All  this  is  overcome  in  these  ma- 
chines. They  can  be  placed  so  as  to  secure  the  best  light,  the 
speed  is  constant,  and  no  power  is  used  in  driving  the  counter- 
shaft when  not  in  use.  The  machines  are  furnished  with  and 
without  stand. 

Fig.  103  shows  a  type  of  polisher  manufactured  by  the  Han- 
son &  Van  Winkle  Co.  It  has  all  the  good  points  of  the 
grinder  (Fig.  94)  manufactured  by  the  same  firm. 


212  ELECTRO-DEPOSITION    OF    METALS. 

The  belt-strapping  attachment  or  endless-belt  machine  shown 
in  Fig.  104  is  made  by  the  above-mentioned  firm.  It  is  sim- 
ple in  construction  and  easily  operated.  It  can  be  used  to 
great  advantage  by  manufacturers  o-f  bicycles  and  bicycle 
parts,  brass  cocks,  and  other  plumbers'  fittings,  gas  fixtures, 
grate  and  fender  work,  while  for  cutlery  it  seems  almost  indis- 
pensable. The  attachment  complete  consists  of  a  12-inch  and 
6-inch  diameter  flanged  pulley,  2J  inches  between  flanges, 
with  standard  and  adjusting  arms. 

,  No  shop  is  now  complete  without  one  or  more  flexible  shafts 
for  grinding,  polishing  and  buffing.     It  will  in  many  ways  be 

FIG.  104. 


found  a  profitable  and  economical  device.  For  cleaning  and 
grinding  heavy  castings,  for  polishing  and  buffing  all  metal 
and  glass,  it  is  an  indispensable  tool  where  power  is  or  can  be 
used  to  advantage.  These  shafts  are  made  in  standard  sizes, 
from  J-inch  diameter  core,  suitable  for  very  light  work,  to  1J- 
oore,  capable  of  driving  a  3-inch  drill  in  iron  or  steel. 

Polishing  materials. — According  to  the  hardness  of  the 
material  to  be  polished,  rouge  (ferric  oxide,  colcothar)  tripoli, 
Vienna  lime,  etc.,  in  the  state  of  an  impalpable  powder,  and 
generally  mixed  with  oil,  or  sometimes  with  alcohol,  are  used 
as  polishing  agents.  For  hard  metals,  an  impalpable  rouge  of 


PREPARATION    OF    THE    METALLIC    OBJECTS.  213 

great  hardness  (No.  F  of  commerce),  is  employed,  for  softer 
metals,  a  softer  rouge  (No.  FFF),  or  Vienna  lime,  tripoli,  etc. 

It  is  of  advantage  to  melt  the  rouge  with  stearine  and  a 
small  quantity  of  tallow,  and  cast  the  mixture  in  moulds  with 
the  aid  of  strong  pressure.  The  sticks  thus  formed  are  suffi- 
ciently greasy  to  render  the  use  of  oil  superfluous.  In  order 
to  impregnate  the  surface  of  the  polishing  bob  with  the  polish, 
ing  material,  hold  one  of  the  sticks  for  a  second  against  the 
revolving  wheel,  and  then  polish  the  objects  by  pressing  them 
against  the  wheel,  diligently  moving  them  to  and  fro.  The 
polishing  bob  must  not  be  too  heavily  impregnated  with  rouge, 
since  a  surplus  of  the  latter  smears  instead  of  cutting  well. 

Ph  polishing  with  Vienna  lime  it  is  expedient  to  moisten  the 
objects  to  be  polished  with  stearine  oil,  and  saturate  the  polish- 
ing wheels  by  pressing  a  piece  of  Vienna  lime  against  them. 
However,  this  causes  a  great  deal  of  dust,  which  not  only 
incommodes  the  workman,  but  is  also  injurious  to  the  respira- 
tory organs.  It  is  therefore  recommended  to  remove  the  dust 
by  means  of  an  exhauster. 

Another  process  of  polishing,  called  burnishing,  is  executed 
by  means  of  tools  usually  made  of  steel  for  the  first  or  ground- 
ing process,  or  of  a  very  hard  stone,  such  as  agate  or  blood- 
stone, for  finishing.  Burnishing  is  applied  to  the  final  polish- 
ing of  deposits  of  the  noble  metals,  and  will  be  referred  to 
later  on. 

B.  MECHANICAL  TREATMENT  DURING  AND  AFTER  ELECTRO-PLATING. 

In  this  connection  scratch-brushing  the  deposits  will  be  first 
considered,  the  object  of  this  operation  being,  on  the  one  hand 
to  promote  the  regular  formation  of  certain  deposits,  and,  on 
the  other,  to  affect  the  physical  properties  of  the  deposits,  and 
finally  to  ascertain  whether  the  deposit  adheres  to  the  basis- 
metal. 

If  it  is  noticed  by  the  irregular  formation  of  the  deposit  that 
the  basis-metal  has  not  been  cleaned  with  sufficient  care  by  the 
preparatory  scratch-brushing,  the  object  has  to  be  taken  from 


214  ELECTRO  DEPOSITION    OF    METALS. 

the  bath  and  the  defective  places  again  scratch-brushed  with 
the  application  of  water  and  sand,  or  puinice  stone,  when  the 
object  is  again  pickled  and  replaced  in  the  bath. 

On  the  other  hand,  the  deposits  always  form  more  or  less 
porous,  they  having,  so  to  say,  a  net-like  structure,  though  it 
may  not  be  visible  to  the  naked  eye.  By  scratch-brushing, 
the  meshes  of  the  net  are  made  closer  by  particles  of  metals 
being  forced  into  them  by  the  brush,  and  the  deposit  is  thus 
rendered  capable  of  receiving  additional  layers  of  metal. 
Furthermore,  by  scratch-brushing,  dull  deposits  acquire  a 
certain  luster,  which  is  enhanced  by  the  subsequent  polishing 
process.  Finally,  by  an  unsparing  application  of  the  scratch- 
brush,  it  will  be  best  seen  whether  the  union  of  the  derj|3it 
with  the  basis-metal  is  sufficiently  intimate  to  stand,  without 
becoming  detached,  the  subsequent  mechanical  treatment  in 
polishing. 

According  to  the  object  in  view,  and  the  hardness  of  the  de- 
posit to  be  manipulated,  scratch-brushes  of  steel  or  brass  wire 
are  chosen.  For  nickel,  which,  as  a  rule,  requires  scratch- 
brushing  least,  and  chiefly  only  for  the  production  of  very 
thick  deposits,  steel  wire  of  0.2  millimeter  thickness  is  taken  ; 
•for  deposits  of  copper,  brass,  and  zinc,  brass  wire  of  0.2  milli- 
meter; for  silver,  brass  wire  of  0.15  millimeter;  and.  for  gold, 
brass  wire  of  0.07  to  0.1  millimeter.  Scratch-brushing  is 
seldom  done  dry.  The  tool  as  well  as  the  pieces  should  be 
constantly  kept  wet  with  liquids,  especially  such  as  produce  a 
lather  in  brushing,  for  instance,  water  and  vinegar,  or  sour 
wine,  or  solutions  of  cream  of  tartar  or  alum,  when  it  is  de- 
sired to  brighten  a  gold  deposit  which  is  too  dark.  However, 
the  liquid  most  generally  used  is  a  decoction  of  licorice-root, 
of  horse-chestnut,  of  marshmallow,  of  soap-wort,  or  of  the  bark 
of  Panama-wood,  all  of  which,  being  slightly  mucilaginous, 
allow  of  a  gentle  scouring  with  the  scratch-brush,  with  the 
production  of  an  abundant  lather.  A  good  adjunct  for 
scratch-brushing  is  a  shallow  wooden  tub  containing  the 
liquid  employed,  with  a  board  laid  across  it  nearly  level  with 


PREPARATION    OF    THE    METALLIC    OBJECTS.  215 

the  edges,  which,  however,  project  a  little  above.  This  board 
•serves  as  a  rest  for  the  pieces. 

The  hand  scratch-brush,  when  operating  upon  small  ob- 
jects, is  held  by  the  workman  in  the  same  manner  as  a  paint 
brush,  and  is  moved  over  the  object  with  a  back  and  forward 
motion  imparted  by  the  wrist  only,  the  forearm  resting  on  the 
edge  of  the  tub.  For  larger  objects,  the  workman  holds  his 
extended  fingers  close  to  the  lower  part  of  the  scratch-brush, 
so  as  to  give  the  wires  a  certain  support,  and,  with  raised 
elbow,  strikes  the  pieces  repeatedly,  at  the  same  time  giving 
the  tool  a  sliding  motion.  When  a  hollow  is  met  with,  which 
•cannot  be  scoured  longitudinally,  a  twisting  motion  is  im- 
parted to  the  tool. 

Scratch-brushing  by  means  of  circular  scratch-brushes  is 
•effected  in  a  lathe.  The  lathe-brush  is  mounted  upon  a 
spindle  and  is  provided  above  with  a  small  reservoir  to  con- 
tain the  lubricating  fluid,  a  small  pipe  with  a  tap  serving  to 
conduct  the  solution  from  this  to  a  point  immediately  above 
the  revolving  brush.  The  top  of  the  brush  revolves  towards 
the  operator,  who  presents  the  object  to  be  scratch-brushed  to 
the  bottom.  The  brush  is  surrounded  by  a  wooden  cage  or 
screen  to  prevent  splashing.  To  protect  the  operator  against 
the  water  projected  by  the  rapid  motion,  there  is  fixed  to  the 
top  of  the  frame  a  small  inclined  board,  which  reaches  a  little 
lower  than  the  axis  of  the  brush  without  touching  it.  This 
board  receives  the  projected  liquid,  and  lets  it  fall  into  a  zinc 
trough,  which  forms  the  bottom  of  the  box.  Through  an 
outlet  provided  in  one  of  the  angles  of  the  trough,  a  rubber 
tube  conveys  the  waste  liquid  to  a  reservoir  below.  After 
scratch-brushing  every  trace  of  the  lubricating  liquid  must  be 
washed  away  before  placing  or  replacing  the  objects  in  the 
bath. 

Drying. — The  finished  plated  objects  are  first  rinsed  in  clean 
water  to  remove  the  solutions  .constituting  the  bath  adhering 
to  them.  They  are  next  immersed  in  hot  water,  where  they 
remain  until  they  have  acquired  the  temperature  of  the  water, 
and  are  then  quickly  dried  in  the  manner  described  on  p.  163. 


216  ELECTRO-DEPOSITION    OF    METALS. 

A  very  good  method  of  freeing  nickeled  objects  from  all' 
moisture  which  may  have  collected  in  the  pores  is  to  immerse 
them  for  about  ten  minutes  in  boiling  linseed  oil,  and,  after 
allowing  them  to  drain  off,  to  remove  the  adhering  oil  by 
rubbing  with  sawdust.  According  to  some  electro-platers,  the 
deposit  of  nickel  thus  treated  loses  its  brittleness  and  will  stand 
bending  several  times,  for  instance,  wire,  sheets,  etc.,  without 
breaking.  Experiments  made  by  Dr.  George  Langbein  did 
not  confirm  these  statements,  but  the  security  against  rust  of 
nickeled-iron  objects  is  found  to  be  considerably  enhanced  by 
boiling  in  linseed  oil. 

Production  of  high  luster. — When  dry,  the  plated  objects  are 
highly  polished,  this  being  effected  by  means  of  polishing 
bobs  of  fine  felt,  cloth  or  flannel,  with  the  use  of  polishing 
compositions,  vienna  lime,  etc.,  or  by  burnishing  with  tools  of 
steel  and  of  agate  or  blood-stone. 

Nickel  deposits  are  almost  without  exception  polished  upon 
cloth  or  felt  bobs  with  rouge  or  Vienna  lime. 

Copper  and  brass  deposits  are  polished  with  fine  flannel  bobs,, 
the  polishing  powder  being  applied  very  sparingly.  Deposits 
of  tin  are  generally  only  scratch-brushed,  it  being  impossible 
10  impart  great  luster  to  this  metal  by  polishing  with  bobs. 
After  drying,  the  deposit  is  polished  with  whiting.  Deposits 
of  gold  and  silver  as  well  as  of  platinum  are  polished  by  burn- 
ishing, the  steel  burnisher  being  used  for  the  grounding  pro- 
cess, and  an  agate  or  blood-stone  burnisher  for  finishing.  The 
operation  of  burnishing  is  carried  on  as  follows  :  Keep  the  tool 
continually  moistened  with  soap-suds.  Take  hold  of  the  tool 
very  near  to  the  end,  and  lean  very  hard  with  it  on  those 
parts  which  are  to  be  burnished,  causing  it  to  glide  by  a  back- 
ward and  forward  motion  without  taking  it  off  the  piece. 
When  it  is  requisite  that  the  hand  should  pass  over  a  large 
surface  at  once  without  losing  its  point  of  support  on  the  work 
bench,  be  careful  in  taking  hold  of  the  burnisher  to  place  it 
just  underneath  the  little  finger.  By  these  means  the  work  is 
done  more  quickly,  and  the  tool  is  more  solidly  fixed  in  the- 


PREPARATION    OF    THE    METALLIC    OBJECTS.  217 

hand.  The  burnishers  are  of  various  shapes  to  suit  the  re- 
quirements of  different  kinds  of  work,  the  first  rough  burnish- 
ing being  often  done  by  instruments  with  comparatively  sharp 
edges,  while  the  finishing  operations  are  accomplished  with 
rounded  ones.  Fig.  105  illustrates  the  most  common  forms 
of  burnishers  of  steel  and  agate.  Both  must  be  free  from 
cracks  and  highly  polished.  To  keep  them  free  from  blem- 
ishes they  are  from  time  to  time  polished  by  vigorously  rub- 
bing them  with  fine  tin  putty,  rouge,  or  calcined  alum  upon* 

FIG.  105. 


a  strip  of  leather  fastened  upon  a  piece  of  wood  which  is  placed' 
in  a  convenient  position  upon  the  work  bench. 

Cleansing  the  polished  objects. — The  objects  to  which  high 
luster  has  been  given  by  means  of  Vienna  lime  and  oil,  or 
rouge,  have  to  be  freed  from  adhering  polishing  dirt.  With 
flat,  smooth  objects,  this  is  effected  by  wiping  with  a  flannel 
rag  and  Vienna  lime,  and  with  those  having  depressions  or 
matted  surfaces,  by  brushing  with  a  soft  brush  and  soap- 
water,  and  then  drying  in  sawdust. 


218  ELECTRO-DEPOSITION    OF    METALS. 

Cleansing  is  very  much  facilitated  by  brushing  the  polished 
articles  upon  a  small  cloth  or  flannel  bob. 

Chemical  Treatment. 

While  it  is  the  aim  of  the  mechanical  treatment  to  prepare, 
on  the  one  hand,  a  pure  metallic  surface,  and  on  the  other,  a 
smooth  one,  the  chemical  preparation  of  the  objects  serves  the 
purpose  of  facilitating  the  mechanical  treatment  by  softening 
and  dissolving  the  impurities  of  the  surface,  and  of  freeing  the 
mechanically  treated  objects  from  adhering  oil,  grease,  dirt, 
etc.,  so  as  to  bring  them  into  the  state  of  absolute  purity  re- 
quired for  the  electro-plating  process. 

Pickling  and  dipping.  The  composition  of  the  pickling 
liquor  varies  according  to  the  nature  of  the  metal  to  be 
treated. 

Cast-iron  and  wrought-iron  articles  are  pickled  in  a  mixture 
of  1  part  by  weight  of  sulphuric  acid  of  66°  Be.  and  15  parts 
by  weight  of  water.* 

To  cleanse  badly  rusted  iron  articles  without  attacking  the 
iron  itself,  it  is  recommended  to  pickle  them  in  a  concentrated 
solution  of  chloride  of  tin,  which,  however,  should  not  contain 
too  much  free  acid,  otherwise  the  iron  is  attacked.  Bucher 
'recommends  a  pickle  composed  as  follows :  Dissolve  3J  ozs. 
of  chloride  of  tin  in  1  quart  of  water,  and  1J  drachms  of  tar- 
taric  acid  in  1  quart  of  water.  Pour  the  former  solution  into 
the  latter,  and  add  20  cubic  centimeters  of  indigo  solution 
diluted  with  2  quarts  of  water.  The  object  of  the  addition  of 
indigo  is  not  intelligible. 

An  excellent  pickle  for  iron  is  also  obtained  by  mixing  10 
quarts  of  water  with  28  ozs.  of  concentrated  sulphuric  acid,  dis- 
solving 2  ozs.  of  zinc  in  the  mixture,  and  adding  12  ozs.  of 
nitric  acid.  This  mixture  makes  the  iron  objects  bright,  while 
dn  dilute  sulphuric  or  hydrochloric  acid  they  become  black. 

Col.  J.  H.  Hansjosten  f  recommends  the  following  pickle  as 

*  The  acid  should  -be  poured  into  the  water,  not  the  water  into  the  acid, 
t  Metal  Industry,  March,  1913. 


PREPARATION    OF    THE    METALLIC    OBJECTS.  219 

giving  good  results  on  cast-iron :  Sulphuric  acid  3  parts, 
hydrofluoric  acid  1  part,  water  3  to  4  parts. 

"  The  length  of  time  required  to  pickle  the  work  in  this 
pickle  depends  on  the  amount  of  scale  on  it,  the  size  of  the 
castings,  and  the  strength  or  weakness  of  the  pickle.  Small 
or  medium  sized  castings  may  be  left  in  it  15  or  20  minutes, 
while  larger  pieces  and  pieces  with  a  large,  smooth  surface, 
should  be  kept  in  longer,  but  the  length  of  time  required  for 
any  class  of  work  may  be  determined  by  the  operator  if  he 
will  watch  the  results  that  the  first  few  batches  will  give. 
He  should  increase  or  decrease  the  strength  of  the  pickle  by 
the  amount  of  water  or  acid  needed,  and  the  condition  of  his 
work  demands.  After  the  castings  are  pickled  they  should  be 
rinsed  in  hot  water  containing  about  J  pound  of  lime  for 
every  10  gallons  of  water.  The  lime  water  serves  a  two-fold 
purpose  in  that  it  neutralizes  the  acid  and  dries  the  castings. 
The  pickle  tank  and  hot  water  tank  should  be  side  by  side  and 
covered  with  a  hood  made  of  \  inch  boards,  high  enough 
above  the  tank  so  that  they  will  not  interfere  with  the  work 
of  the  operator,  but  not  so  high  that  it  will  not  carry  off  the 
fumes  and  steam  caused  by  the  acid  and  lime  water.  The 
top  of  the  hood  should  slant  downward  over  the  tanks  from  a 
pipe  or  stack  leading  upward,  so  as  to  aid  the  natural  draft 
that  will  carry  the  steam  and  fumes  away.  If  the  hood  ends 
so  that  the  fumes  will  be  guided  into  a  smokestack  or  chim- 
ney, no  exhaust  will  be  necessary,  as  the  natural  draft  will 
carry  them  away. 

"  Wood  boxes,  with  the  nails  driven  well  into  the  wood  and 
of  convenient  size,  with  holes  bored  in  the  sides  and  bottom, 
.and  iron  wires  of  sufficient  strength  and  long  enough  so  that 
the  ends  will  remain  above  the  solution  when  attached  to  the 
box  as  a  handle,  make  good  baskets  for  small  work.  Larger 
pieces  with  holes  in  them  may  be  strung  on  iron  wire,  and  the 
ends  looped  together,  so  as  to  be  convenient  to  take  out. 
Pieces  of  the  same  kind  may  be  reversed  ;  that  is,  put  face  to 
face  or  back  to  back,  so  that  they  will  not  nest  and  thus  pre- 


220  ELECTRO-DEPOSITION    OF    METALS. 

vent  the  acid  from  attacking  them  all  over.  Large  quantities 
of  work  may  be  quickly  handled  in  this  way,  and,  by  making 
the  tank  of  proper  length,  the  operator  may  begin  to  put  in 
work  at  one  end  and  work  toward  the  other,  and  by  the  time 
the  tank  is  filled  the  work  put  in  first  is  nearly  ready  to  come 
out.  It  is  better  to  have  the  tank  run  to  size  in  length  rather 
than  in  breadth  or  depth.  A  tank,  30  inches  wide,  18  inches 
deep,  and  5  or  6  feet  long,  will  be  large  enough  to  pickle  the 
work  for  20  to  30  polishers.  Acid  should  be  added  to  the 
pickle  as  it  weakens,  and  when  it  becomes  too  old  it  should  be 
thrown  away  and  a  new  one  made  up.  Lime  should  be 
added  to  the  lime  water  every  day  or  so.  Both  solutions 
may  be  kept  in  working  order  for  a  very  long  time  by  simply 
keeping  them  up  to  the  required  strength.  No  set  rule  can 
be  laid  down  to  go  by  in  adding  acid,  or  how  long  the  work 
should  remain  in  the  pickle.  This  must  be  ascertained  by  the 
operator,  and  a  little  experience  will  quickly  tell  him  what  to- 
do  and  when  to  do  it. 

"  The  scratch-brushing  may  also  be  made  a  factor  in  turn- 
ing out  good  work,  but  is  important  only  in  a  relative  way. 
If  it  is  improperly  done,  particles  of  sand  may  remain  in  the 
places  where  the  polishing  wheel  will  not  reach,  and  in  the 
finished  piece  will  show  up  as  black  spots.  The  cost  of 
scratch-brushing  is  so  little,  however,  that  it  will  be  well 
worth  while  to  pay  some  attention  to  it,  and  if  the  pickling  is 
properly  done,  it  is  only  necessary  to  brush  the  loose  sand  out 
of  the  background.  An  objection  to  pickling  that  has  been 
raised  is  that  the  acid  will  ooze  out  of  the  work  after  plating 
and  discolor  it.  This  may  occur  if  the  work  is  pickled  too 
much,  but  a  little  care  will  overcome  it,  or  will  not  allow  it  to 
happen  at  all.  All  time  and  attention  given  to  this  part  of 
the  preparatory  process  will  be  amply  repaid,  as  the  result 
cannot  be  otherwise  than  a  lower  cost  in  polishing." 

For  many  cases  pickling  may  advantageously  be  effected  in 
the  electrolytic  way.  Suspend  the  articles  in  a  weak  acid 
bath  (hydrochloric  or  sulphuric  acid),  connect  them  with  the 


PREPARATION    OF    THE    METALLIC    OBJECTS.  221 

positive  pole  of  a  source  of  current,  and  suspend  opposite  to 
them  a  sheet  of  metal  (copper  or  brass),  which  is  connected 
with  the  negative  pole. 

According  to  a  patent  of  the  Vereinigten  Elektrischen 
Gesellschaften,  Vienna  and  Buda-Pest,  a  20-per  cent,  alkaline 
solution  of  common  salt  or  of  Glauber's  salt  is  used  for  elec- 
trolytic pickling,  the  metal  to  be  pickled  serving  as  anode. 
By  the  passage  of  the  current,  the  electrolyte  is  broken  up  into 
sodium-ions,  which  are  separated  on  the  cathodes,  and  S04 
and  chlorine-ions,  which  are  separated  on  the  anodes,  the 
pickling  effect  being  produced  by  the  latter  ions. 

This  electrolyte  may  also  be  used  for  freeing  sheet  metal, 
for  instance,  sheet-iron,  which  is  to  be  zincked,  from  grease, 
-and  at  the  same  time  pickling  it.  For  this  purpose  the  sheet- 
iron  is  suspended  to  the  anode  and  object-rods  of  the  bath,  and 
a  current  allowed  to  enter  through  the  anodes,  the  sheets 
serving  as  cathodes  being  thereby  freed  from  grease  by  the 
secondarily  formed  caustic  soda.  When  this  has  been  done, 
the  direction  of  the  current  is  reversed,  the  former  cathodes 
becoming  now  the  anodes,  and  the  former  anodes,  the  cathodes. 
The  first  having  been  previously  freed  from  grease  are  now 
pickled  by  the  separated  anions,  while  the  latter  are  freed  fro 
grease.  When  pickling  is  finished,  the  sheets  which  have 
served  last  as  anodes,  are  taken  from  the  bath  and  replaced  by 
fresh  sheets,  and  the  direction  of  the  current  having  been 
changed,  the  operation  is  repeated,  a  continuous  .process  of 
freeing  from  grease  and  pickling  being  thus  possible.  With 
about  90  amperes  and  4  volts  per  square  meter,  pickling,  ac- 
cording to  the  "  Metallarbeiter,"  requires  about  half  an  hour. 

To  render  possible  the  removal  in  the  electrolytic  way  of  the 
layer  of  hard  solder  remaining  after  soldering  bicycle  frames 
and  thus  to  allow  of  perfect  enameling,  the  following  method 
is,  according  to  Burgess,*  generally  adopted  in  this  country. 
The  parts  to  be  soldered  together  were  simply  dipped  in  hard 

*  Electro-chemical  Industry,  1904,  No.  1. 


222  ELECTRO-DEPOSITION    OF    METALS. 

solder  whereby  a  thin  layer  of  hard  solder  remained  upon  the 
parts  thus  treated.  To  remove  this  by  filing  proved  expensive, 
and  to  dissolve  by  cyanides  and  solutions  of  double  chromates 
required  much  time,  and  was  imperfect.  With  the  assistance 
of  the  electric  current  and  the  use  of  a  suitable  electrolyte  the 
hard  solder  is  completely  and  rapidly  removed  without  attack- 
ing the  steel.  A  suitable  electrolyte  for  the  purpose  is  a  5-per 
cent,  sodium  nitrate  solution.  In  consequence  of  electrolysis 
some  sodium  nitrate  is  formed,  and  thjs  makes  the  iron  or 
steel  passive,  i.  e.,  deprives  it  of  the  power  to  be  attacked  by 
the  electrolyte,  while  the  hard  solder  is  completely  dissolved. 
It  must,  however,  be  borne  in  mind  that  after  several  days' 
electrolysis  the  steel  does  no  longer  remain  passive,  but  is  per- 
ceptibly attacked  by  the  electrolytic  pickle,  this  being  due  to 
the  Fact  that  the  electrolyte  becomes  alkaline  and  then  con- 
tains free  ammonia.  The  latter  must  therefore  be  every  day 
neutralized  by  the  addition  of  dilute  sulphuric  acid.  The 
sodium  nitrate  used  for  the  preparation  of  the  electrolyte 
should  not  contain  much  chloride,  as  otherwise  the  iron  is 
attacked. 

The  correct  progress  of  the  operation  is  recognized  by  the 
rapid  solution  of  the  hard  solder,  a  brown  layer  remaining 
behind,  which  can  readily  be  rubbed  off.  If,  however,  a  thick, 
greenish,  firmly  adhering  slime  forms  on  the  anodes,  the  elec- 
trolyte has  become  alkaline,  and  when  a  brownish  foam  and 
precipitate  appear  upon  the  surface  of  the  ^electrolyte,  the  alka- 
linity has  become  so  great  that  the  steel  is  also  attacked.  The 
hard  solder  electrolytically  dissolved  from  the  steel  frame  is 
precipitated  as  copper  and  zinc  hydroxide  by  the  caustic  soda 
secondarily  formed  on  the  cathode.  This  precipitate  has  from 
time  to  time  to  be  removed  from  the  bath.  The  most  suitable 
current-density  is  0.8  to  1.2  amperes  with  3  to  5  volts. 

The  duration  of  pickling  depends  on  the  more  or  less  thick 
layer  of  scale,  etc.,  which  is  to  be  removed  or  softened.  The 
process  may  be  considerably  assisted  and  the  time  shortened 
by  frequent  scouring  with  sand  or  pumice.  The  pickled 


PREPARATION    OF    THE    METALLIC    OBJECTS.  223 

articles  are  rinsed  in  cold  water,  then  immersed  in  hot  water, 
and  dried  in  sawdust.  In  order  to  neutralize  the  acid  remain- 
ing in  the  pores,  it  is  advisable  to  make  the  rinsing  water 
alkaline  by  the  addition  of  caustic  potash  or  soda,  etc. 

Zinc  objects  are  only  pickled  when  they  show  a  thick  layer 
of  oxide,  in  which  case  pickling  is  also  effected  in  dilute  sul- 
phuric or  hydrochloric  acid,  and  brushing  with  fine  pumice. 
A  very  useful  pickle  for  zinc  consists  of  sulphuric  acid  100 
parts  by  weight,  nitric  acid  100,  and  common  salt  1.  The 
zinc  objects  are  immersed  in  the  mixture  for  one  second,  and 
then  quickly  rinsed  off  in  water  which  should  be  frequently 
changed. 

Copper,  and  its  alloys  brass,  bronze,  tombac  and  German  silver, 
are  cleansed  and  brightened  by  dipping  in  a  mixture  of  nitric 
acid,  sulphuric  acid,  and  lampblack,  a  suitable  pickle  consist- 
ing of  sulphuric  acid  of  66°  Be.,  50  parts  by  weight,  nitric  acid 
of  36°  Be.,  100,  common  salt  1,  and  lampblack  1.  In  order 
to  remove  the  brown  coating,  due  to  cuprous  oxide,  the  objects 
are  first  pickled  in  dilute  sulphuric  acid,  and  then  dipped  for 
a  few  seconds,  with  constant  agitation,  in  the  above-mentioned 
pickle  until  they  show  a  bright  appearance.  They  are  then 
immediately  rinsed  in  water  to  check  any  further  action  of 
the  pickle. 

If  objects  of  copper  or  its  alloys  are  not  to  be  subjected,  after 
pickling,  to  further  mechanical  treatment,  or  are  to  be  at  once 
placed  in  the  electro-plating  bath,  it  is  best  to  execute  the 
pickling  process  in  two  operations  by  treating  them  in  a  pre- 
liminary pickle  and  brightening  them  in  the  bright- dipping 
bath.  The  preliminary  pickle  consists  of  nitric  acid  of  36°  Be., 
200  parts  by  weight,  common  salt  1,  lampblack  2.  In  this 
preliminary  pickle  the  articles  are  allowed  to  remain  until  all 
impurities  are  removed,  when  they  are  rinsed  in  a  large 
volume  of  water,  dipped  in  boiling  water,  so  that  they  quickly 
dry,  and  plunged  into  the  bright-dipping  bath,  which  consists 
of  nitric  acid  of  40°  Be.,  75  parts  by  weight,  sulphuric  acid  of 
66°  Be.,  100,  and  common  salt  1.  It  is  not  advisable  to  bring 


224  ELECTRO-DEPOSITION    OF    METALS.    ' 

the  objects  which  have  passed  through  the  preliminary  pickle 
and  rinsing  water  directly,  while  still  moist,  into  the  bright- 
dipping  bath,  since  for  the  production  of  a  beautiful,  pure 
luster  the  introduction  of  water  into  the  bright-dipping  bath 
must  be  absolutely  avoided. 

Hence  the  objects  treated  in  the  preliminary  pickle  should 
first  be  dried  by  heating  in  hot  water,  shaking  the  latter  off. 

Potassium  cyanide,  dissolved  in  ten  times  its  weight  of 
water,  is  often  used  instead  of  the  acid  pickle  for  brass,  es- 
pecially when  it  is  essential  that  the  original  polish  upon  the 
objects  should  not  be  destroyed,  as  in  the-  preparation  of 
articles  for  nickel-plating.  The  objects  should  remain  in  this 
liquid  longer  than  in  the  acid  pickle,  because  the  metallic 
oxides  are  far  less  soluble  in  this  than  in  the  latter.  In  all 
cases  the  final  cleaning  in  water  must  be  observed. 

All  acid  pickles  used  for  different  kinds  of  work  should  be 
kept  distinct  from  each  other,  so  that  one  metal  may  not  be 
dipped  into  a  solution  containing  a  more  electro-negative 
metal,  which  would  deposit  upon  it  by  chemical  exchange. 

The  pickled  objects  must  not  be  unnecessarily  exposed  to 
the  air,  and  should  be  transferred  as  quickly  as  possible  from 
the  pickle  to  the  wash-waters,  and  then  to  the  electro-plating 
bath,  or,  if  this  is  not  feasible,  kept  under  pure  water.  Pickled 
objects  which  are  not  to  be  plated  are  carefully  washed  in 
water,  which  should  be  frequently  changed,  then  rinsed, 
drawn  through  a  solution  of  tartar,  and  dried  by  dipping  in 
hot  water  and  rubbing  with  sawdust. 

Places  soldered  with  soft  solder,  as  well  as  parts  of  iron, 
become  black  by  pickling,  and  have  to  be  brightened  by 
scouring  with  pumice,  or  by  scratch-brushing. 

Mat-dipping.  Objects  of  brass  or  other  alloys  of  copper 
are  frequently  to  be  given  a  dead  surface  so  that  after  plating 
they  show  a  beautiful  mat  luster.  Very  fine  effects  may  by 
this  means  be  obtained,  especially  in  the  bronze-ware  industry. 
Matting  may  be  effected  in  various  ways.  Every  bright  dip 
acts  as  a  mat  dip  if  the  objects  are  exposed  to  its  effect  for  a 


PREPARATION    OF    THE    METALLIC    OBJECTS.  225 

longer  time  and  at  a  higher  temperature.  Matting  is,  how- 
ever, made  more  effective  by  adding  zinc  sulphate  to  the  dip, 
the  matting  being  the  more  pronounced,  the  more  zinc  sul- 
phate has  been  added. 

A  good  mat  dip  is  prepared  by  pouring  a  solution  of  0.35 
oz.  of  zinc  sulphate  in  3|  ozs.  of  water  in  a  cold  mixture  of 
6J  Ibs.  of  nitric  acid  of  36°  Be.,  4.4  Ibs.  of  sulphuric  acid  of 
•66°  Be.,  and  J  oz.  of  common  salt.  According  to  the  shade 
of  mat  desired,  the  objects  are  allowed  to  remain  in  the  dip 
for  2  to  10  minutes.  The  objects,  which  on  coming  from  the 
mat-dip  show  a  faded,  earthy  appearance,  are  rapidly  drawn 
through  a  clean  bright  dip,  whereby  they  acquire  the  mat 
luster,  and  are  then  quickly  rinsed  in  a  large  volume  of  water. 

For  the  production  of  a  mat-grained  surface  by  pickling, 
the  following  mixture  may  be  recommended  :  Saturated  solu- 
tion of  potassium  dichromate  1  part  by  volume,  and  concen- 
trated hydrochloric  acid  2  parts  by  volume.  In  this  mixture 
the  brass  articles  are  allowed  to  remain  several  hours.  They 
are  then  rapidly  drawn  through  the  bright-dipping  bath  and 
rinsed  in  a  larger  volume  of  water  frequently  renewed. 

A  delicate  matted  surface  may  be  produced  by  electrolytic 
pickling  or  etching.  The  process  is  the  same  as  described 
above  under  iron. 

Other  methods  of  matting  will  be  given  under  "  Gilding." 

Generally  speaking,  it  may  be  said  that  less  depends  on  the 
•composition  of  the  pickle  than  on  quick  and  skilful  manipula- 
tion ;  and  as  good  results  have  always  been  obtained  with  the 
above-mentioned  mixture,  there  is  no  reason  for  repeating  the 
innumerable  receipts  given  for  pickles.  The  main  points  are  to 
have  the  acid  mixture  as  free  from  water  as  possible,  further  to 
develop  hyponitric  acid  which  is  effected  by  the  reduction  of 
nitric  acid  in  consequence  of  the  addition  of  organic  substances 
(lampblack,  sawdust,  etc.),  and  of  chlorine,  which  is  formed  by 
the  action  of  the  sulphuric  acid  upon  the  common  salt.  The 
volume  of  the  dipping  bath  should  not  be  too  small,  since  in 
pickling  the  acid  mixture  becomes  heated  and  the  increased 
15 


226 


ELECTRO-DEPOSITION    OF    METALS. 


temperature  shows  a  very  rapid,  frequently  not  controllable, 
action,  so  that  a  corrosion  of  small  articles  may  readily  take 
place.  It  is  therefore  necessary  to  allow  the  acid  mixture^ 
after  its  preparation,  to  thoroughly  cool  off.  Pour  the  sul- 
phuric acid  into  the  nitric  acid  (never  the  reverse !)  and  allow 
the  mixture,  which  thereby  becomes  strongly  heated,  to  cool 
off  to  at  least  the  ordinary  temperature. 

In  order  to  be  sure  of  the  uniform  action  of  the  pickle  upon 
all  parts,  it  is,  in  all  cases,  advisable  previous  to  pickling  to 

FIG.  106. 


free  the  articles  from  grease  by  one  of  the  methods  given 
later  on. 

In  pickling  abundant  vapors  are  evolved  which  have  an  in- 
jurious effect  upon  the  health  of  the  workmen,  and  corrode 
metallic  articles  exposed  to  them.  The  operation  should, 
therefore,  be  conducted  in  the  open  air,  or  under  a  well- 
drawing  vapor-flue. 

In  large  establishments  it  may  happen  that  the  quantity  of 
escaping  acid  vapors  is  so  large  as  to  become  a  nuisance  to  the 
neighborhood,  which  the  proprietors  may  be  ordered  by  the 


PREPARATION    OF    THE    METALLIC    OBJECTS.  227 

authorities  to  abate.  The  evil  is  best  remedied  by  a  small 
absorbing  plant,  as  follows : 

Connect  the  highest  point  of  the  vapor-flue  D  (Fig.  106)  by 
a  wide  clay  pipe  E  with  a  brick  reservoir,  A,  laid  in  cement, 
so  that  R  enters  A  a  few  centimeters  above  the  level  of  the 
fluid,  kept  constantly  at  the  same  height  by  the  discharge  pipe 
b.  Above,  the  reservoir  is  closed  by  an  arch  through  which 
the  water  conduit  IF  is  introduced.  Below  the  sieve  S,  which 
is  made  of  wood  and  coated  with  lacquer,  a  wide  clay  pipe  R 
leads  to  the  chimney  of  the  steam  boiler ;  or  the  suction  pipe 
of  an  injector  is  introduced  in  this  place,  into  which  the  air 
from  the  vapor- flue  is  sucked  through  the  reservoir  and 
allowed  to  escape  into  the  open  air  or  into  a  chimney. 
Through  the  man-hole  M,  the  sieve-bottom  S  of  the  reservoir 
is  filled  with  large  pieces  of  chalk  or  limestone.  The  manner 
of  operating  is  now  as  follows  :  A  thin  jet  of  water  falls  upon 
S,  where  it  is  distributed  and  runs  over  the  layer  of  chalk. 
The  air  of  the  pickling  room  saturated  with  acid  vapor  moves 
upward  in  consequence  of  the  draught  of  the  chimney  of  the 
steam  boiler,  the  injector,  or  the  ventilator,  and  yields  its  con- 
tent of  acid  to  the  layer  of  chalk,  while  the  neutral  solution 
of  calcium  nitrate  and  calcium  chloride,  which  is  thus  formed, 
runs  off  through  b. 

The  absorption  of  the  acid  vapors  may,  of  course,  be  effected 
by  apparatus  of  different  construction,  but  the  one  above  de- 
scribed may  be  recommended  as  being  simple,  cheap,  and 
effective. 

The  considerable  consumption  of  acid  for  pickling  purposes 
in  large  establishments  makes  it  desirable  to  regain  the  acid 
and  metal  contained  in  the  exhausted  dipping  baths.  The 
following  process  has  proved  very  successful  for  this  purpose  : 
Mix  the  old  dipping  baths  with  J  their  volume  of  concentrated 
sulphuric  acid,  and  bring  the  mixture  into  a  nitric  acid  distill- 
ing apparatus.  Distil  the  nitric  acid  off  at  a  moderate  temper- 
ature, condense  it  in  cooled  clay  coils,  and  collect  it  in  glass 
balloons.  To  the  residue  in  the  still  add  water,  precipitate 


228  ELECTRO-DEPOSITION    OF    METALS. 

from  the  blue  solution,  which  contains  sulphate  of  copper  and 
zinc,  the  copper  with  zinc  wasteland  add  zinc  until  evolution 
of  hydrogen  no  longer  takes  place.  Filter  off  the  precipitated 
copper  through  a  linen  bag,  wash,  and  dry.  The  fluid  run- 
ning off,  which  contains  zinc  sulphate,  is  evaporated  to  crystal- 
lization and  yields  quite  pure  zinc  sulphate,  which  may  be 
sold  to  dye-works,  or  for  the  manufacture  of  zinc-white. 

According  to  local  conditions,  for  instance,  if  the  zinc  sul- 
phate cannot  be  profitably  sold  in  the  neighborhood,  or  zinc 
waste  cannot  be  obtained,  it  may  be  more  advantageous  to  omit 
the  regaining  of  zinc  from  the  dipping  baths.  In  this  case  the 
fluid  which  is  obtained  by  mixing  the  contents  of  the  still  with 
water  is  compounded  with  milk  of  lime  until  it  shows  a  slightly 
acid  reaction.  The  gypsum  formed  is  allowed  to  settle,  and 
after-bringing  the  supernatant  .clear  fluid  into  another  reservoir, 
the  copper  is  precipitated  by  the  introduction  of  old  iron.  The 
first  rinsing  waters  in  which  the  pickled  objects  are  washed 
are  treated  in  the  same  manner.  The  precipitated  copper  is 
washed  and  dried. 

Removal  of  grease  and  cleansing.  These  two  operations  must 
be  executed  with  most  painstaking  exactness  because  on  them 
chiefly  depends  the  success  of  the  electro-plating  process. 
Their  object  is  to  remove  every  trace  of  impurity,  be  it  due  to 
the  touching  with  the  hands  or  to  the  manipulation  in  grind- 
ing and  polishing,  and  to  get  rid  of  the  layer  of  oxide  which 
is  formed  in  removing  the  grease  with  lyes  and  other  agents. 

According  to  the  preparatory  treatment  of  the  articles,  the 
removal  of  grease  is  a  more  or  less  complicated  operatiorK 
Large  quantities  of  oily  or  greasy  matter  should  be  removed 
by  washing  with  benzine  or  petroleum,  it  being  advisable  to 
execute  this  operation  immediately  after  grinding  and  polish- 
ing, so  that  the  oil  used  in  these  operations  has  no  chance  of 
hardening,  as  is  frequently  the  case  with  articles  preparatively 
polished  with  Vienna  lime  and  stearine  oil.  Instead  of  clean- 
ing with  benzine  or  petroleum,  the  articles,  as  far  as  their 
nature  allows,  may  be  boiled  in  a  hot  lye  consisting  of  1  part 


PREPARATION    OF    THE    METALLIC    OBJECTS.  229 

of  caustic  potash  or  soda  in  10  of  water,  until  all  the  grease  is 
saponified,  when  the  dirt,  consisting  of  grinding  powder,  can  be 
readily  removed  by  brushing.  In  place  of  solution  of  caustic 
alkalies,  hot  solution  of  soda  or  potash  may  be  used,  but  its 
action  is  much  slower  and  offers  no  advantages.  Objects  of 
tin,  lead  and  Britannia  must  be  left  in  contact  with  the  lye 
for  a  short  time  only,  as  otherwise  they  are  attacked  by  it. 

The  articles  thus  freed  from  the  larger  portion  of  grease  are 
first  rinsed  in  water,  and  then,  for  the  removal  of  the  last  traces 
of  grease,  are  brushed  with  a  bristle  brush  and  a  mixture  of 
water,  quicklime  and  whiting  until,  when  rinsed  in  water,  all 
portions  appear  equally  moistened  and  no  dry  spots  are  visible. 

The  lime  mixture  or  paste  is  prepared  by  slaking  freshly- 
burnt  lime,  free  from  sand,  with  water  to  an  impalpable  pow- 
der, mixing  1  part  of  this  with  1  part  of  fine  whiting,  and 
adding  water,  stirring  constantly,  until  a  paste  of  the  con- 
sistency of  syrup  is  formed. 

The  shape  of  many  objects  presents  certain  difficulties  in  the 
removal  of  grease,  as  the  deeper  portions  cannot  be  reached 
with  the  brush,  as,  for  instance,  in  skates,  which  often  are  to 
be  nickeled  in  a  finished  state.  In  this  case  the  objects  are 
drawn  in  succession  through  three  different  benzine  vessels. 
In  the  first  benzine  most  of  the  grease  is  dissolved,  the  rest  in 
the  second,  while  the  third  serves  for  rinsing  off.  When  the 
benzine  in  the  first  vessel  contains  too  much  grease,  it  is  emp- 
tied and  filled  with  fresh  benzine,  and  then  serves  as  the  third 
vessel,  while  that  which  was  formerly  the  second  becomes  the 
first,  and  the  third  the  second.  After  rinsing  in  the  third  ben- 
zine vessel,  the  objects  are  plunged  in  hot  water,  then  for  a  few 
seconds  dipped  in  thin  milk  of  lime,  and  finally  thoroughly 
rinsed  in  water.  It  is  recommended  not  to  omit  the  treatment 
with  milk  of  lime  of  objects  freed  from  grease  with  benzine. 

Electro-chemical  cleaning.  It  has  been  found  that  alkaline 
substances,  such  as  sodium  carbonate,  potassium  carbonate, 
potassium  hydroxide  and  sodium  hydroxide  in  solution,  in 
varying  degrees  of  concentration  and  with  small  proportions  of 


230  ELECTRO-DEPOSITION    OF    METALS. 

potassium  cyanide  added,  will  with  a  sufficiently  strong  electric 
current  of  from  4  to  8  volts,  and  at  a  temperature  nearly  boil- 
ing, develop  sufficient  hydrogen  to  remove  entirely  all  organic 
substances  from  the  surface  of  the  metal,  thereby  leaving  it 
chemically  clean. 

This  method  has  brought  into  the  market  several  new  com- 
binations which  are  sold  under  the  name  of  electro-chemical 
cleaning  salts,  and  have  given  very  satisfactory  results. 

In  a  paper  read  at  the  convention  of  the  American  Brass 
Founders'  Association,  at  Toronto,  Canada,  1908,  Charles  H. 
Proctor,  in  speaking  of  electro-chemical  cleaning  baths  and 
their  application,  says  :  * 

"  The  action  of  an  electro-cleanser  is  similar  to  the  action  of 
an  electro-plating  bath.  The  only  difference  as  far  as  the  de- 
velopment of  gases  is  concerned,  is  that  no  metal  being  in 
solution  and  the  anode  being  insoluble,  no  metal  is  deposited. 
But  with  a  strong  current  a  copious  evolution  of  oxyhydrogen 
gas  is  developed  upon  the  articles,  which  attacks  the  organic 
matter  upon  the  surface,  practically  lifting  it  off  and  by  rapid 
evolution  of  the  gases  carries  it  to  the  surface.  The  small 
quantity  of  potassium  cyanide  contained  in  solution  absorbs 
the  slight  oxidation  that  might  be  upon  the  surface,  and  by 
the  combined  action  produces  a  surface  clean  enough,  after 
washing  in  clear  water,  for  any  deposits. 

"The  arrangement  of  an  electro-cleaning  bath  is  very 
simple.  Prepare  a  wrought-iron  tank  of  proportions  best 
adapted  to  the  amount  of  work  to  be  cleansed.  This  should 
be  heated  with  steam  coils  of  iron.  Across  the  top  of  the 
tank  an  insulated  frame  should  be  constructed.  Upon  this 
frame  place  three  conducting  poles,  as  on  the  regular  plating 
bath.  To  the  two  outside  poles  the  positive  current  should 
be  carried  direct.  This  can  best  be  accomplished  with  at 
least  J-inch  copper-wire  flexible  cables.  To  the  center  pole 
the  negative  current  is  connected  with  cables  of  the  same 

*  The  Metal  Industry,  June,  1908. 


PREPARATION    OF    THE    METALLIC    OBJECTS.  231 

dimensions  ;  no  rheostats  are  necessary.  The  stronger  the 
current  the  greater  the  evolution  of  gases  and  the  quicker  the 
cleansing  operation  is  accomplished. 

"  Although  direct  contact  can  be  made  with  the  positive 
•current  to  the  tank  itself,  in  practice  better  results  have  been 
obtained  with  anodes  of  sheet-iron  not  more  than  6  inches 
wide  and  of  a  length  in  proportion  to  the  depth  of  the  tank. 

"  The  electro-cleaning  solution  should  consist  (for  ordinary 
purposes)  of  3  to  4  ozs.  caustic  potash  to  each  gallon  of  water, 
and  to  every  100  gallons  of  solution  8  ozs.  cyanide  of  potas- 
sium. This  can  be  varied  according  to  conditions.  It  is  ad- 
visable to  add  at  least  J  Ib.  cyanide  each  week.  Where  the 
articles,  such  as  iron  or  steel,  contain  much  oil  or  grease  upon 
the  surface,  the  density  of  the  solution  can  be  increased.  For 
articles  of  brass,  copper  or  bronze  that  have  been  polished, 
use  a  solution  of  carbonate  of  soda  in  the  proportion  of  2  ozs. 
soda  and  J  oz.  caustic  potash  to  each  gallon  of  water,  with 
the  addition  of  4  ozs.  of  cyanide  to  every  100  gallons  of  solu- 
tion. If  much  organic  matter  is  upon  the  surface  of  the 
articles  to  be  cleansed,  it  is  advisable  where  an  air  pressure 
can  be  obtained  from  an  ordinary  blower,  to  arrange  a  pipe  so 
that  the  current  of  air  can  be  deflected  upon  the  surface  of  the 
solution,  thus  keeping  the  center  of  the  solution  clear  of  the 
insoluble  substances  that  arise  to  the  surface.  When  the 
cleanser  is  at  rest,  as  much  of  this  matter  should  be  removed 
as  possible. 

"  It  should  be  the  aim  of  the  operator  to  use  the  same 
methods  of  avoiding  all  unnecessary  contamination  as  he 
would  in  electro-depositing  baths.  It  is  obvious  even  to  those 
who  have  not  practiced  this  method  of  cleansing  metallic 
articles  that  large  quantities  of  work  can .  be  treated  very 
rapidly,  and  this  is  the  case  especially  where  frames  or  racks 
are  used  in  the  plating  operations.  On  account  of  the  rapidity 
of  operation  and  the  efficiency  of  the  bath,  this  method  of 
•cleansing  should  be  a  part  of  the  labor-saving  devices  used  in 
all  great  commercial  establishments  engaged  in  the  electro- 
plating of  metals." 


232 


ELECTRO-DEPOSITION    OF    METALS. 


To  avoid  subsequent  touching  with  the  hands  the  objects,, 
before  freeing  them  from  grease,  must  of  course  be  tied  to  the 
metallic  wires  (of  soft  copper)  by  which  they  are  suspended  in 
the  electro-plating  bath.  In  removing  the  grease  by  the  wet 
method  a  layer  of  oxide  scarcely  perceptible  to  the  eye  is  fre- 
quently formed  upon  the  metals.  This  layer  of  oxide  has  to 
be  removed,  the  liquid  used  for  the  purpose  varying,  of  course, 
with  the  nature  of  the  layer. 


FIG.  107. 


FIG.  108, 


Objects  of  iron  and  steel,  as  well  as  of  zinc,  are  momentarily 
plunged  in  a  mixture  of  sulphuric  acid  1  part  by  weight  and 
water  20  parts,  and  quickly  rinsed  off  in  clean  water.  Highly 
polished  objects  of  iron  and  steel,  after  being  treated  with  this 
mixture,  are  best  again  rapidly  brushed  with  lime  paste,  and,, 
after  rinsing  off  quickly,  immediately  brought  into  the  electro- 
plating bath. 

Copper,   brass,   bronze,   German  silver,  and   tombac   are    best 


PREPARATION    OF    THE    METALLIC    OBJECTS.  233- 

cleaned  with  a  dilute  solution  of  potassium  cyanide,  1  part  of 
60-per  cent,  potassium  cyanide  in  15  to  20  of  water.  The 
objects  are  then  quickly  rinsed  off  and  placed  in  the  electro- 
plating bath. 

Lead  and  Britannia  may  be  treated  with  water  slightly 
acidulated  with  nitric  acid. 

The  difficult  and  dangerous  operation  of  tilting  heavy  carboys 
containing  acid  is  overcome  by  the  use  of  the  Hanson  &  Van 
Winkle  acid  pump  shown  in  Figs.  107  and  108.  In  using  this 
pump  it  is  not  necessary  for  two  men  to  handle  a  carboy.  A 
workman  carries  the  acid  pitcher  or  receptacle  to  the  carboy; 
one  end  of  the  pump  tube  is  placed  in  the  acid,  the  rubber- 
cork  making  an  air-tight  joint  in  the  neck  of  the  carboy,  and 
the  other  end  of  the  pump  is  carried  to  the  pitcher.  On 
pumping  a  steady  flow  of  acid  is  obtained. 

Electro-plating  Solutions  (Electrolytes,  Baths). 

Next  to  the  proper  mechanical  and  chemical  preparations 
of  the  objects,  the  success  of  the  process  of  electro-deposition- 
depends  on  the  suitable  composition  of  the  electro-plating 
solutions,  electrolytes,  or  baths,  and  the  proper  current-strength 
which  is  conducted  into  the  baths  for  the  precipitation  of  the 
metals.  In  regard  to  the  latter  .the  most  essential  conditions 
have  already  been  discussed  in  Chap.  IV.,  "Electro-plating 
Plants  in  General,"  and  will  be  further  referred  to  in  speaking 
of  the  several  electro-plating  processes.  Hence,  the  general 
rules  which  have  to  be  observed  in  the  preparation  of  the 
baths  will  first  be  considered. 

Solvents. — With  the  exception  of  the  baths  prepared  with 
glycerin  according  to  the  patent  of  Marino,  water  is  the  solvent 
used  in  the  preparation  of  all  baths,  and  its  constitution  is  by 
no  means  of  such  slight  importance  as  is  frequently  supposed. 

Spring  and  well  waters  often  contain  considerable  quantities- 
of  lime,  magnesia,  common  salt,  iron,  etc.,  the  presence  of 
which  may  cause  various  kinds  of  separations  in  the  baths. 
On  the  other  hand,  river  water  is  frequently  impregnated  to- 


234  ELECTRO-DEPOSITION    OF    METALS. 

such  an  extent  with  organic  substances  that  its  employment 
without  previous  purification  cannot  be  recommended.  No 
doubt,  distilled  water,  or  in  want  of  that  rain  water,  is  the 
most  suitable  for  the  preparation  of  baths.  However,  rain 
water  collected  from  metal  roofs  should  not  be  used,  nor  that 
running  off  from  other  roofs,  it  being  contaminated  with  dust. 
When  used,  it  should  be  caught  in  vessels  of  glass,  earthen- 
ware, or  wood,  free  from  tannin,  and  filtered.  Where  river  or 
well  water  has  to  be  employed,  thorough  boiling  and  filtering 
before  use  are  absolutely  necessary  in  order  to  separate  the 
carbonates  of  the  alkaline  earths  held  in  solution.  By  boiling, 
a  possible  content  of  sulphuretted  hydrogen  is  also  driven  off. 

Purity  of  chemicals.  Another  important  factor  is  the  purity 
of  the  chemicals  used  for  the  baths,  the  premature  failure  of 
the  latter  being  in  most  cases  caused  by  the  unsuitable  nature 
of  the  chemicals,  which  also  frequently  gives  rise  to  abnormal 
phenomena  inexplicable  to  the  operator.  Chloride  of  zinc,  for 
instance,  may  serve  as  an  example.  It  is  found  in  commerce 
in  very  varying  qualities,  it  being  prepared  for  dyeing  pur- 
poses with  about  70  per  cent,  actual  content  of  chloride  of 
;zinc,  for  pharmaceutical  purposes  with  about  90  per  cent.,  and 
.for  electro-plating  purposes  with  98  or  99  per  cent.  Now  it 
will  readily  be  seen  that  if  an  operator  who  is  preparing  a 
brass  bath  according  to  a  formula  which  calls  for  pure  chloride 
of  zinc  uses  a  preparation  intended  for  dyeing  purposes,  there 
will  be  a  deficiency  of  metallic  zinc  in  the  bath,  and  the  con- 
tent of  copper  in  the  bath  being  too  large  in  proportion  to  the 
zinc  present,  will  cause  reddish  shades  in  the  deposit. 

Likewise,  in  case  the  operator  uses  potassium  cyanide  of  low 
•content,  when  the  formula  calls  for  a  pure  article  with  98  per 
cent.,  he  will  not  be  able  to  effect  the  solution  of  copper  or 
zinc  salts  with  the  quantity  prescribed.  Furthermore,  potas- 
sium cyanide,  in  the  preparation  of  which  prussiate  of  potash 
•containing  potassium  sulphate  is  used,  will  cause,  by  reason  of 
the  formation  of  potassium  sulpho-cyanide,  various  disturbing 
influences  (formation  of  bubbles  in  the  deposit),  the  explana- 


PREPARATION    OF    THE    METALLIC    OBJECTS.  235 

tion  of  which  is  difficult  to  the  operator,  who,  trusting  to  the 
purity  of  the  chemicals,  seeks  elsewhere  for  the  causes  of  the 
abnormal  phenomena. 

Sodium  sulphite  may  in  similar  manner  cause  great  annoy- 
ance if  the  suitable  preparation  is  not  used.  There  is  a  crystal- 
ized  neutral  salt  which  is  employed  for  many  gold  baths,  and 
also  the  bisulphite  of  soda  in  the  form  of  powder  which  serves 
for  the  preparation  of  copper  and  brass  baths.  If  the  latter 
should  be  used  in  the  preparation  of  gold  baths,  the  gold 
would  be  reduced  from  the  solution  of  its  salts  and  precipitated 
as  a  brown  powder. 

Or,  if  in  preparing  nickel  baths,  a  salt  containing  copper  is 
used,  the  nickeling  will  never  be  of  a  pure  white  color,  but 
show  shades  having  not  even  a  distant  resemblance  to  the 
color  of  nickel. 

The  above-mentioned  examples  will  suffice  to  show  how 
careful  the  operator  must  be  in  the  selection  of  the  sources 
from  which  he  obtains  his  supplies.  It  may  be  here  men- 
tioned that  all  the  directions  given  in  the  following  pages 
refer  to  chemically  pure  products ;  where  products  of  a  lower 
standard  may  be  used  their  strength  is  especially  given. 

Concentration  of  baths. — For  the  concentration  of  the  various 
baths  no  general  rules  can  be  laid  down  ;  neither  can  the  de- 
termination of  the  density  of  the  baths  by  the  hydrometer  be 
relied  on.  If  electro-plating  solutions  consisted  of  nothing 
but  the  pure  metallic  salts,  the  specific  gravity,  which  is  indi- 
cated by  the  hydrometer-degrees,  might  serve  for  an  estimation 
of  their  value.  But  such  an  estimation  is  often  apt  to  prove 
deceptive,  since,  to  decrease  the  resistance,  the  baths  also  re- 
quire conducting  salts,  and  by  the  addition  of  a  larger  quantity 
of  them,  the  specific  gravity  of  a  bath  may  be  increased  to 
any  extent  without  the  content  of  the  more  valuable  metal 
being  greater  than  in  a  bath  showing  fewer  hydrometer-degrees. 

When  the  operator  is  acquainted  with  the  composition  of 
the  baths,  and  knows  how  many  degrees  Be.  a  fresh  bath 
should  show  when  correctly  prepared,  he  can  draw  a  con- 


236  ELECTRO-DEPOSITION    OF    METALS. 

elusion  as  to  the  condition  of  the  bath  by  changes  in  the 
specific  gravity.  If,  for  instance,  a  nickel  bath  when  freshly 
prepared  shows  the  standard  specific  gravity — 70°  Be. — for 
nickel  baths,  and  it  shows  later  on  90°  Be.,  the  greater  spe- 
cific gravity  is  due  either  to  evaporation  of  water  or  to  excessive 
refreshing  or  strengthening  of  the  bath.  Such  a  bath  gen- 
erally yields  dark  or  spotted  nickeling,  the  deposit  is  formed 
in  a  sluggish  manner,  and  readily  scales  off  with  a  stronger 
current.  The  operator  in  this  case  may  recognize  from  the 
hydrometer  that  the  cause  of  these  phenomena  is  not  due  to  a 
contamination  of  the  bath,  but  to  its  over-concentration. 
Baths,  when  too  concentrated,  readily  deposit  salts  in  crystals 
on  the  anodes  and  the  sides  of  the  tanks,  which  should  by  no 
means  take  place,  and  there  is  even  danger  of  microscopic 
crystals  depositing  upon  the  articles  and  causing  holes  in  the 
deposit. 

A  plating  bath  should  never  be  poor  in  metal,  as  otherwise 
it  soon  becomes  exhausted,  and  besides  the  deposits  form  more 
slowly  and  with  less  density  than  in  baths  with  a  correct  con- 
tent of  metal. 

Hence  in  summer  when  the  temperature  of  the  bath,  is 
naturally  higher,  they  can  be  made  more  concentrated  than  in 
winter.  If  crystals  are  separated,  even  when  a  bath  shows  a 
temperature  of  58°  F.,  they  should  be  removed  and  dissolved 
in  hot  water.  The  solution  is  returned  to  the  bath  and  water 
is  added  to  the  latter  until  the  formation  of  crystals  ceases. 

Agitation  of  the  baths. — In  order  that  all  the  strata  of  the 
bath  may  show  an  equal  content  of  metal,  it  is  advisable  in 
the  evening,  after  the  day's  work  is  done,  to  thoroughly  stir 
up  the  solution  with  a  wooden  crutch.  For  practical  reasons 
the  baths  are  generally  made  one-quarter  to  one-third  deeper 
than  corresponds  to  the  lengths  of  the  objects  io  be  plated.  In 
consequence  of  this,  the  strata  of  fluid  between  the  anodes  and 
the  objects  become  poorer  in  metal  than  those  on  the  bottom,, 
and  the  object  of  stirring  up  is  to  restore  the  same  concentra- 
tion to  all  portions  of  the  bath. 


PREPARATION    OF    THE    METALLIC    OBJECTS.  237 

While  stirring  up  the  bath,  it  is  also  advisable  to  see  whether 
any  metallic  articles  have  become  detached  from  the  slings 
and  dropped  to  the  bottom  of  the  vat.  Such  articles  must  be 
taken  out,  since  they  are  dissolved  by  some  baths,  the  latter 
being  thereby  spoiled.  This  examination  must  be  especially 
thorough  with  nickel  baths. 

The  strata  of  fluid  which  come  in  contact  with  the  anodes 
become,  by  the  absorption  of  metal,  specifically  heavier  than 
the  other  strata  and  sink  to  the  bottom  of  the  tank,  while,  on 
the  other  hand,  the  strata  of  fluid  which  yield  metal  to  the 
articles  become  specifically  lighter  and  rise  to  the  top.  A 
partial  compensation,  of  course,  takes  place  by  diffusion,  but 
not  a  complete  one,  and  from  this  cause  arise  several  annoy- 
ances. The  heavier  and  more  saturated  fluid  offering  greater 
resistance  to  the  current,  the  anodes  are  attacked  chiefly  on 
the  upper  portions  where  the  specifically  lighter 
layer  of  fluid  is;  practically  this  is  proved  by  the 
appearance  of  the  anodes,  which,  at  first  square, 
after  being  for  some  time  used,'  assume  the  shape 
shown  in  Fig.  109. 

On  the  other  hand,  the  portions  of  the  cathodes 
(objects)  which  come  in  contact,  near  the  surface, 
with  strata  of  fluid  poor  in  metal,  acquire  a  deposit 
of  less  thickness  than  the  lower  portions  which  dip 
into  the  bath  where  it  is  richer  in  metal.     Now  if 
the  bath  also  contains  free  acid,  and  if  there  is  a  considerable^ 
difference  in  the  specific  gravity  of  the  lower  and  upper  strata 
of  fluid,  the  electrode,  which  touches  both  strata,  produces  a 
current,  the  effect  of  which  is  that  metal  dissolves  from  the 
upper  portions  and  deposits  upon  the  lower.     This  explains 
the  phenomenon  that  a  deposit  on  the  upper  portions  of  the 
objects  may  be  redissolved,  even  when  a  current,  which,  how- 
ever, must  be  very  weak,  is  conducted  into  the  bath  from  an 
external  source. 

Many  authors,  therefore,  go  so  far  as  to  demand  that  during 
the  electro-plating  process  the  baths  should  be  kept  in  con- 


238  ELECTRO-DEPOSITION    OF    METALS. 

f 

slant  agitation  by  mechanical  means.  This,  however,  is- 
scarcely  necessary,  because  a  homogeneity  of  the  solution  is 
to  a  certain  extent  effected  by  the  agitation  of  the  fluid  in 
suspending  and  taking  out  the  objects.  Hence  as  long  as 
objects  are  put  in  and  taken  out,  an  agitation  naturally  takes 
place  in  which  all  the  strata  of  fluid  between  the  objects  arid 
anodes  take  part,  while  only  the  deepest  strata,  which  do  not 
come  into  contact  with  the  objects  and  the  anodes,  remain  in 
a  state  of  stagnation. 

Constant  agitation  of  the  plating  solution  is  of  advantage  in 
silvering,  and  in  galvanoplastic  reproduction  in  the  acid  copper 
bath,  in  which  the  articles  have  to  remain  four  to  five,  and  eight 
to  ten  hours.  With  constant  agitation  of  the  bath  it  is  possi- 
ble to  work  with  a  greater  electro-motive  force,  whereby  the 
deposits  are  finished  in  a  shorter  time ;  and  in  silvering,  the 
formation  of  current-streaks  is,  to  a  certain  extent,  avoided  ; 
and  in  galvanoplastic  reproduction,  the  formation  of  so-called 
blooms.  In  nickeling,  with  constant  agitation  of  the  bath, 
heavier  deposits  can,  without  doubt,  be  obtained  in  a  shorter 
time  and  without  premature  deadening  of  the  deposit. 

Henry  Sand  *  draws  attention  to  the  fact  that,  according  to 
'all  known  experience,  the  greater  current-densities  which  are 
permissible  in  the  electrolysis  of  given  metal  salt  solutions,  de- 
pend solely  on  the  rapidity  of  the  renewal  of  the  fluid  on  the 
electrode.  In  his  opinion  it  is  very  probable  that,  in  the  depo- 
fcsition  of  metals,  the  cathode  potential  in  itself  is  independent 
of  the  current-density,  further  that  the  quality  of  the  metal 
deposits  is  but  slightly  influenced  by  the  current-density,  and 
that  the  greater  variations  in  the  nature  of  the  deposits  with 
different  current-densities  is  almost  exclusively  due  to  local 
changes  in  concentration. 

These  changes  in  concentration — the  impoverishment  in 
metal  ions  of  the  electrolyte  on  the  place  where  it  comes  in 
contact  with  the  cathode — is  according  to  Daneel  f  caused,  on 

*  Zeitschrift  fur  Elektrochemie,  1904,  S.  452. 
f  Zeitschrift  fur  Elektrochemie,  IX,  763. 


PREPARATION   OF    THE    METALLIC    OBJECTS.  239' 

the  one  hand,  by  the  separation  of  metal  ions  on  the  cathode; 
further,  in  complex  salt  solutions,  by  the  accumulation  of  ions 
of  the  salt  which  with  the  metal  salt  forms  the  complex  com- 
bination, and  by  the  conveyance  by  the  current  of  the  metal 
in  those  complex  salt  solutions  which  form  complex  anions 
containing  the  metal  to  be  separated,  and  migrate  away  from 
the  cathode  to  the  anode. 

The  impoverishment  in  metal  ions  would  proceed  still  more 
rapidly  but  for  the  counter-action  of  certain  forces.  First  of 
all,  diffusion  has  to  be  taken  into  consideration  ;  it  causes  the 
entrance  of  strata  of  fluid  richer  in  metal  into  those  poorer  in 
metal,  and  it  is  greatest  on  the  sides  where  impoverishment  has 
progressed  furthest.  Further,  fresh  ions  are  constantly  sup- 
plied by  dissociation,  and  by  solutions  of  the  simple  as  well  as 
the  complex  salts  which  contain  the  metal  in  the  cation, 
impoverishment  is  counteracted  by  the  conveyance  of  metal 
by  the  current. 

When  working  with  low  current-densities  in  an  electrolyte, 
even  when  the  latter  is  at  rest,  the  slighter  concentration  of 
ions  appearing  on  the  cathode  is  to  a  certain  extent  obviated 
by  diffusion  of  fluid  richer  in  metal ;  hence  under  such  condi- 
tions good  deposits  are  obtained  without  agitation  of  the  elec- 
trolyte. 

The  case,  however,  is  different  when  in  the  same  electrolyte 
depositions  are  made  with  high  current-densities,  serviceable 
deposits  being  only  obtained  so  long  as  sufficient  concentration 
of  metal  ions  is  present  on  the  points  of  contact  of  the  electro- 
lyte with  the  cathode.  However,  as  diffusion  is  no  longer 
sufficiently  great  to  replace  the  content  of  metal  separated, 
hydrogen  ions  are  next  separated,  together  with  the  metal 
ions  supplied  by  diffusion,  which  causes,  almost  without  ex- 
ception, the  formation  of  spongy  deposits.  Hence  in  rapid 
electrolysis  for  which  high  current-densities  are  employed,  the 
local  exhaustion  of  the  layers  on  the  cathode  has  to  be  pre- 
vented by  vigorous  agitation  of  the  electrolyte. 

Constant  agitation  effects  also  the  more  rapid  removal  of 


240  ELECTRO-DEPOSITION    OF    METALS. 

the  hydrogen-bubbles  which  form  on  the  articles,  but  the  same 
end  is  attained  without  complicated  contrivances  by  the  oper- 
ator accustoming  himself  to  strike  the  object-rod  a  slight  blow 
with  the  finger  each  time  he  suspends  an  object. 

Temperature  of  the  baths.  The  temperature  required  for  the 
electro-plating  solutions  has  already  been  referred  to  on  p. 
120,  where  also  the  means  have  been  given  for  bringing  baths 
which  have  cooled  down  too  much  to  the  proper  degree  of 
temperature.  Baths  which  are  to  be  used  cold  should  under 
no  circumstances  show  a  temperature  below  59°  F.,  it  being 
best  to  maintain  them  at  between  64.5°  and  68°  F. 

The  warmer  a  bath  is,  the  less  its  specific  resistance  and  the 
greater  its  conducting  power,  because  the  salts  dissolved  in  the 
bath  are  more  dissociated  than  when  the  electrolyte  is  cold. 
In  warm  solutions  the  hydrogen-bubbles  separated  by  the 
cathodes  escape  much  more  rapidly  than  in  cold  electrolytes, 
and  consequently  there  is  less  chance  of  hydrogen  occlusion 
which,  according  to  general  opinion,  is  the  principal  cause  of 
the  deposit  peeling  off. 

Boiling  the  baths. — Boiling  is  required  in  the  preparation  of 
many  baths,  if,  after  cooling,  they  are  to  yield  good  and  cer- 
tain results.  The  kettles  and  boiling-pans  used  for  the  purpose 
are  of  various  shapes,  hemispherical  or  with  flat  bottom,  and 
are  made  of  different  materials,  those  of  enameled  iron,  or, 
.for  small  baths,  of  porcelain  or  earthenware,  being  best.  The 
enamel  of  the  iron  kettles  must  be  of  a  composition  which  is 
not  attacked  by  the  bath.  Notwithstanding  their  enamel  these 
vessels  become  gradually  impregnated  with  the  solutions  they 
have  .held,  and  it  is  risky  to  employ  them  for  different  kinds 
of  baths.  Thus,  an  enameled  kettle  which  has  been  used  for 
silvering  will  not  be  suitable,  even  after  the  most  thorough 
washing,  for  a  gold  bath,  as  the  gilding  will  certainly  be  white 
or  green,  according  to  the  quantity  of  silver  retained  by  the 
vessel.  The  use  of  metal  vessels  should  be  avoided.  Copper 
and  brass  baths  may,  however,  be  boiled  in  strong  copper 
kettles,  though  they  are  somewhat  attacked.  A  copper  kettle, 


PREPARATION    OF    THE    METALLIC    OBJECTS.  241 

after  being  freed  from  grease  and  scoured  bright,  may  be  pro- 
vided with  a  thick  deposit  of  nickel  by  filling  it  with  a  nickel 
bath,  connecting  it  with  the  negative  pole  of  a  strong  battery 
or  dynamo  machine,  and  suspending  it  in  a  number  of  nickel 
anodes  connected  with  the  positive  pole.  Such  nickeled  kettles 
may  be  used  for  boiling  nickel  baths,  but  enameled  kettles  or 
large  dishes  of  nickel-sheet,  or  vessels  lined  with  lead,  deserve 
the  preference.  Generally  speaking,  nickel  baths  do  not  re- 
quire actual  boiling,  but  the  nickel  salts  and  certain  conduct- 
ing salts  which  constitute  the  baths,  dissolve  with  difficulty 
in  cold  water,  and  hence  solution  is  effected  in  hot  water. 

When,  for  the  preparation  of  nickel  baths,  nickel  salts  soluble 
with  difficulty  have  to  be  dissolved  with  the  assistance  of  heat, 
and  no  suitable  vessel  is  available  for  the  purpose,  solution 
may  be  effected  as  follows :  Bring  pure  water  in  a  bright  cop- 
per kettle  to  the  boiling-point.  Pour  the  hot  water  into  a 
clean  wooden  bucket  holding  from  8  to  10  quarts,  and  add  the 
quantity  of  nickel  salt  corresponding  to  the  quantity  of  water. 
Stir  with  a  wooden  crutch  until  solution  is  complete.  Repeat 
the  operation  until  all  the  salt  required  is  dissolved. 

For  very  large  baths  this  process  would,  however,  require 
too  much  time,  and  it  is,  therefore,  advisable  to  use  a  large 
round  or  oval  wooden  tank,  or  a  tank  lined  with  pure  sheet 
lead.  The  contents  of  the  tank  are  heated  by  means  of  a  lead 
•coil  through  which  steam  is  introduced. 

Working  the  baths  with  the  current.  In  case  boiling  of  large 
quantities  of  fluid  is  not  feasible,  the  same  object  may  be  at- 
tained by  working  the  bath  for  some  time  with  the  electric  cur- 
rent. The  anode  rods  are  hung  full  of  anodes  and,  a  few  plates 
of  the  same  kind  of  metal  having  been  secured  to  the  object- 
rods,  a  current  of  medium  strength  is  conducted  into-  the  bath 
until  an  object,  from  time  to  time  suspended  in  the  bath,  is 
properly  covered  with  a  deposit.  This  process  is  frequently 
used  with  great  success  for  large  brass  baths. 

Objections  have  been  made  to  the  process  because  it  is  some- 
times carried  too  far,  the  solution  becoming  thereby  demetai- 
16 


242  ELECTRO-DEPOSITION    OF    METALS. 

lized  (?).  However,  there  is  no  reason  for  objecting  to  a  pro- 
cess because  some  operators  carry  it  out  in  a  bungling  manner, 
and  in  our  opinion  a  bath  which  cannot  stand  working  for 
several  days  with  the  current  without  becoming  poor  in  metal 
is  not  of  the  proper  composition. 

Filtering  the  baths.  Should  the  solutions  after  their  prepa- 
ration, and,  if  necessary,  boiling,  not  be  perfectly  clear,  they 
have  to  be  filtered.  For  large,  baths  this  is  best  effected  by 
means  of  felt  filter  bags,  and  for  smaller  baths,  especially  those 
of  the  noble  metals,  with  filtering  paper.  This  removal  of 
the  particles  held  in  suspension  is  necessary  to  prevent  their 
deposition  upon  the  objects,  which  might  cause  small  holes  in 
the  deposit,  as  well  as  roughness  and  other  defects.  It  is  still 
better  to  allow  the  baths  to  clarify  by  standing  quietly,  and 
to  draw  off  the  clear  solution  by  means  of  a  siphon.  The 
turbid  residue  is  then  filtered. 

Prevention  of  impurities.  To  secure  lasting  qualities  to  the 
baths  they  must  be  carefully  protected  from  every  possible 
contamination.  When  not  in  use  for  plating  they  should  be 
covered  to  keep  out  dust.  The  objects  before  being  placed  in 
the  baths  should  be  free  from  adhering  scouring  material  or 
dipping  fluid,  which  otherwise  might,  in  time,  spoil  the  bath. 
The  cleansing  of  the  anode  and  object  rods  by  means  of  sand- 
paper, or  emery-paper,  should  never  be  done  over  the  bath, 
so  as  to  avoid  the  danger  of  the  latter  being  contaminated  by 
the  oxides  of  the  metal  constituting  the  rods  falling  into  it. 
When  a  visible  layer  of  dust  has  collected  upon  the  bath,  it 
must  be  removed,  as  otherwise  particles  of  dust  might  deposit 
upon  the  objects  and  prevent  an  intimate  union  of  the  deposit 
with  the  basis-metal.  With  large  baths  the  removal  of  the 
layer  of  dust  is  readily  effected  by  drawing  a  large  piece  of 
filtering  or  tissue  paper  over  the  surface,  and  repeating  the 
operation  with  fresh  sheets  of  clean  paper  until  all  the  dust  is 
removed.  Small  baths  should  be  filtered. 

Ttie  choice  of  anodes  is  also  an  important  factor  for  keeping 
the  baths  in  good  condition,  as  well  as  for  obtaining  good 


PREPARATION    OF    THE    METALLIC    OBJECTS.  243 

results.  The  anodes  should  always  consist  of  the  metal  which 
is  deposited  from  the  solution;  and  the  metal  used  for  them 
must  be  pure  and  free  from  all  admixtures.  To  replace  as 
much  as  possible  the  metal  withdrawn  from  the  bath  by  the 
electro-plating  process,  the  anodes  must  be  soluble;  and  it  is 
wrong  if,  for  instance,  nickel  baths  are  charged  with  insoluble 
anodes  of  carbon;  or  for  smaller  baths,  of  sheet  platinum, 
provided  the  chemical  composition  of  the  bath  does  not  in 
part  demand  insoluble  anodes.  Insoluble  anodes  cause  a 
steady  and  rapid  declination  in  the  content  of  metal,  an  ex- 
cessive formation  of  acid  in  the  bath,  and,  by  the  detachment 
of  particles  of  carbon,  a  contamination  of  the  solution. 
Further  particulars  in  regard  to  anodes  will  be  given  in  dis- 
cussing the  separate  baths. 

Absorption  of  the  deposit.  When  upon  a  pure  metallic  sur- 
face another  metal  is  electro-deposited,  the  first  portion  of  the 
deposit  penetrates  into  the  basis-metal,  thus  forming  an  alloy. 
This  may  be  readily  proved  by  repeating  Gore's  experiments. 
If  a  thick  layer  of  copper  be  precipitated  upon  a  platinum 
sheet,  and  then  heated  to  a  dark-red  heat,  the  deposit  can  be 
entirely  peeled  off.  By  then  heating  the  platinum  sheet  with 
nitric  acid,  and  thoroughly  washing  with  water,  it  appears, 
after  drying,  entirely  white  and  pure.  By  reheating  the  sheet, 
the  surface  becomes  again  blackened  by  cupric  oxide,  and  by 
frequently  repeating  the  same  operation,  a  fresh  film  of  cupric 
oxide  will  always  be  obtained. 

This  penetration  of  the  deposit  into  the  basis-metal,  how- 
ever, does  not  merely  take  place  during  electro-plating,  but 
also  later  on ;  and  it  may  frequently  be  observed  that,  for  in- 
stance, zinc  objects  only  slightly  coppered  or  brassed,  after 
some  time  become  again  white.  Since  this  also  happens  when 
the  deposits  are  protected  by  a  coat  of  lacquer  against  atmos- 
pheric influences,  the  only  explanation  of  the  phenomenon 
can  be  that  the  deposit  is  absorbed  by  the  basis-metal,  which 
is  also  confirmed  by  analysis.  This  fact  must  be  taken  into 
consideration  if  durable  deposits  are  to  be  produced. 


244  ELECTRO-DEPOSITION    OF    METALS. 

Effect  of  the  current-density.  A  greater  or  smaller  current- 
density  used  in  operating  is  not  without  influence  upon  the 
electrolytes.  The  greater  the  current-density  is,  the  more 
metal  will  be  deposited  on  the  cathode,  while  on  the  anode 
the  oxidation  of  the  metal  and  its  solution  into  acid  residues 
cannot  take  place  in  the  same  measure,  the  result  being 
further  decompositions,  oxygen  gas  being  liberated.  In  con- 
sequence of  this  there  appear  also  greater  differences  in  con- 
centration than-  when  depositing  with  less  current-density  and, 
as  regards  concentration,  the  electrolyte  will  remain  most 
constant  when  working  with  a  smaller  current-density. 

For  depositions  upon  strongly  profiled  objects  a  medium 
current-strength  will  prove  most  suitable.  Daneel  *  pictures 
the  process  as  follows :  If  a  deposit  is  made  upon  an  article 
with  elevations  and  depressions,  the  current  lines  will  crowd 
together  towards  the  elevated  points,  i.  e.,  those  nearer  to  the 
anodes,  since  the  current  always  chooses  the  most  convenient 
way.  Now  owing  to  the  deposit  an  impoverishment  in  metal 
in  the  electrolyte  takes  place  on  the  elevated  portions,  and  the 
consequence  is  that  on  these  portions  the  separation-tension'  is 
increased.  However,  when  the  latter  is  increased  the  current- 
lines  will  turn  towards  more  favorable  portions  richer  in  metal 
ions,  i.  e.,  those  lying  deeper,  until  an  impoverishment  in  metal 
ions  there  also  takes  place.  From  this  it  follows  that  with  a 
medium  current-strength  the  current-lines  cannot  permanently 
favor  any  particular  portions  of  the  cathodes,  and  the  deposit 
must  become  uniform.  Should  an  unequal  impoverishment 
take  place  on  the  electrode  it  would  be  overcome  by  short- 
closed  circuits  formed  there,  which  means  that  they  cannot 
distribute  themselves  unequally  over  the  surface  of  the  cathode. 

With  very  small  current-densities  the  process  would  be  dif- 
ferent. When  the  current-density  is  so  small  that  an  im- 
poverishment in  metal  ions  on  the  entire  electrode  can  be 
prevented  by  diffusion,  the  current-lines  will  permanently 

*  Zeitschrift  fur  Elektrochemie,  IX,  763. 


PREPARATION    OF    THE    METALLIC    OBJECTS.  245 

crowd  together  upon  the  more  elevated  portions,  and  the 
deposit  will  grow  there,  while  less  metal  deposits  in  the 
depressions. 

In  practice  it  has  been  found  that  a  great  distance  of  the 
anodes  from  the  profiled  cathodes,  thorough  agitation  of  the 
electrolyte,  not  too  great  a  conductivity  of  the  latter,  and  a 
normal  current-density,  are  the  best  auxiliaries  for  obtaining 
deposits  of  uniform  thickness,  and  where  these  do  not  suffice 
recourse  may  be  had  for  depressions  to  the  hand  anode  (see 
later  on). 

Current  output.  In  the  theoretical  part  it  has  already  been 
stated  that  the  separation-products  of  electrolysis  are  fre- 
quently subject  to  secondary  decomposition.  Thus,  the  hydro- 
gen escaping  on  the  cathodes  means  a  loss  of  electrolyzing 
effect  of  the  current,  and  it  is  obvious  that  the  quality  of  the 
deposit  obtained  does  thereby  not  come  up  to  the  values  which, 
according  to  the  laws  of  Faraday,  should  be  obtained.  The 
quantities  of  deposit  produced  in  practice  referred  to  the  theo- 
retically calculated  quantities,  are  called  the  current-output. 

Reaction  of  the  baths.  A  distinction  is  made  between  acid, 
alkaline,  neutral,  and  potassium  cyanide  baths.  The  reaction 
of  a  bath  is  determined  by  means  of  suitable  reagent  papers. 
Thus,  blue  litmus  paper,  for  instance,  indicates  the  acid  nature 
of  a  bath  when  by  being  dipped  in  it,  it  acquires  a  red  color. 
All  acids  redden  blue  litmus  paper,  though  many  metallic 
salts  of  a  perfectly  neutral  character  produce  the  same  change 
in  color,  and  it  is  therefore  necessary  to  make  additional  tests. 
TropaBolin  paper,  for  instance,  which  possesses  a  yellow  color, 
is  only  changed  by  mineral  acids,  the  yellow  color  being  con- 
verted into  violet.  A  bath,  which  reddens  blue  litmus  paper 
and  colors  tropseolin  paper  violet,  contains  without  doubt,  a 
free  inorganic  acid,  while  a  bath  which  only  reddens  blue 
litmus  paper,  but  does  not  change  tropseolin  paper  does  not 
contain  a  free  inorganic  acid,  but  an  organic  acid  (citric? 
tartaric  acids),  and  with  a  content  of  certain  inorganic  salts 
may  also  be  free  from  organic  acid. 


246  ELECTRO-DEPOSITION    OF    METALS. 

An  alkaline  reaction  of  the  bath  is  indicated  by  red  litmus 
paper  acquiring  a  blue  color,  while  neither  blue  or  red  litmus 
paper  is  changed  when  the  electrolyte  is  neutral. 

In  a  normal  state,  potassium  cyanide  baths  always  show  an 
alkaline  reaction ;  deviations  from  this  condition  will  be  later 
on  referred  to. 

The  general  qualifications  which  an  electro-plating  bath 
should  possess  are  as  follows : 

1.  It  should  possess  good  conducting  power. 

2.  It  must   exert  a  sufficient  dissolving   effect    upon  the 
anodes. 

3.  It  must  reduce  the  metal  in  abundance  and  in  a  reguline 
state. 

4.  It  must  not  be  chemically  decomposed  by  the  metals  to 
be  plated,  hence  not  by  simple  immersion ;  the  adherence  of 
the  deposit  to  the  basis-metal  being  in  this  case  impaired. 

5.  It  must  not  be  essentially  decomposed  by  air  and  light. 


CHAPTER  VI. 

DEPOSITION    OF    NICKEL    AND    COBALT. 
1.     DEPOSITION  OF  NICKEL,  (Ni  =  58.68  PARTS  BY  WEIGHT). 

ALTHOUGH  nickel-plating  is  of  comparatively  recent  origin, 
it  shall  be  first  described,  since  chiefly  by  reason  of  the  devel- 
opment of  the  dynamo-electrical  machine  it  has  steadily  grown 
in  popularity  and  become  an  industry  of  great  magnitude  and 
importance.  The  great  popularity  which  nickel-plating  enjoys 
is  due  to  the  excellent  properties  of  the  nickel  itself — the 
almost  silvery  whiteness  of  the  metal,  its  cheapness  as  com- 
pared with  silver,  and  the  hardness  of  the  electro-deposited 
metal,  which  gives  the  coating  great  power  to  resist  wear  and 
abrasion  ;  its  capability  of  taking  a  high  polish  ;  the  fact  that 
it  is  not  blackened  by  the  action  of  sulphurous  vapors  which 
rapidly  tarnish  silver,  and  finally  the  fact  that  it  exhibits  but 
little  tendency  to  oxidize  even  in  the  presence  of  moisture. 

Properties  of  nickel. — Pure  nickel  is  a  lustrous,  silvery-white 
metal  with  a  slight  steel-gray  tinge.  Its  specific  gravity  varies 
from  8.3  (cast  nickel  plates)  to  9.3  (wrought  or  rolled  plates). 
It  is  slightly  magnetic  at  the  ordinary  temperature,  but  loses 
this  property  when  heated  to  680°  F.  It  melts  at  about  the 
same  temperature  as  iron,  but  is  more  fusible  when  combined 
with  carbon. 

The  metal  is  soluble  in  dilute  nitric  acid,  concentrated  nitric 
acid  rendering  it  passive,  i.  e.,  insoluble.  In  hydrochloric  and 
sulphuric  acids  it  dissolves  very  slowly,  especially  when  in  a 
compact  state. 

Certain  articles,  for  instance,  hot  fats,  strongly  attack  nickel, 
while  vinegar,  beer,  mustard,  tea  and  other  infusions  produce 
stains ;  hence,  the  nickeling  of  culinary  utensils  or  the  use  of 

(247) 


248  ELECTRO-DEPOSITION    OF    METALS. 

nickel-plated  sheet  iron  for  that  purpose  cannot  be  recom- 
mended. 

Nickel  salts.  The  first  requisite  in  preparing  nickel  baths  is 
the  use  of  absolutely  pure  chemicals,  and  in  choosing  the  nickel 
salts  to  be  especially  careful  that  they  are  free  from  salts  of  iron, 
copper  and  other  metals.  Furthermore,  it  is  not  indifferent 
what  kind  of  nickel  salt  is  used,  whether  nickel  chloride,  nickel 
sulphate,  the  double  sulphate  of  nickel  and  ammonium,  etc.,  but 
the  choice  of  the  salt  depends  chiefly  on  the  nature  of  the  metal 
which  is  to  be  nickeled.  There  are  a  large  number  of  general 
directions  for  nickel  baths,  of  which  nickel  chloride,  ammonio- 
nickel  chloride,  nickel  nitrate,  etc.,  form  the  active  constituents, 
and  yet  it  would  be  a  grave  mistake  to  use  these  salts  for  nick- 
eling iron,  because  the  liberated  acid  if  not  immediately  and 
completely  fixed  by  the  anodes  in  dissolving,  imparts  to  the  iron 
objects  a  great  tendency  to  the  formation  of  rust.  Iron  objects 
nickeled  in  such  a  bath,  to  be  sure,  come  out  faultless,  but  in  a 
short  time,  even  if  stored  in  a  dry  place,  portions  of  the  nickel 
layer  will  be  observed  to  peel  off,  and  by  closely  examining 
them  it  will  be  seen  that  under  the  deposit  a  layer  of  rust  has 
formed  which  actually  tears  the  nickel  off.  The  use  of  nickel 
sulphates  or  of  the  salts  with  organic  acids  is,  therefore  consid- 
ered best.  It  might  be  objected  that  the  liberated  sulphuric 
acid  produces  in  like  manner  a  formation  of  rust  upon  the 
iron  objects ;  but  according  to  long  experience  and  many  thor- 
ough examinations,  such  is  not  the  case,  the  tendency  to  the 
formation  of  rust  being  only  imparted  by  the  use  of  the  chlo- 
ride and  nitrate. 

Of  the  nickel  salts  with  organic  acids,  the  citrate  and  tar- 
trate  have  been  frequently  employed.  Nickel  citrate  in  watery 
solution  is  not  particularly  well  dissociated,  requires  a  greater 
electro-motive  force  and  is  quite  indifferent  towards  variations 
in  the  latter,  this  being  the  chief  reason  for  its  use  in  nickel- 
ing sharp  ground  instruments.  Nickel  lactate,  according  to 
Jordis's  patent,*  yields,  to  be  sure,  beautiful,  lustrous  deposits 

*  Jordis,  Elektrolyse  wassriger  Metallsalzlosungen,  S.  78. 


DEPOSITION    OF    NICKEL    AND    COBALT. 

in  thin  layers,  but  is  not  serviceable  for  heavy  nickeling,., 
since,  as  the  inventor  himself  admits,  deposits  in  thicker 
layers  tear.  Of  materially  greater  advantage  is  the  use  of  the 
combinations  of  nickel  with  the  ethyl  sulphates  *  and  their 
derivatives.  According  to  experiments  made  in  Dr.  Lang- 
bein's  laboratory,  the  ethyl  sulphate  solutions  of  metals  are 
very  energetically  dissociated  and  permit  the  production  of 
very  thick  deposits  without  peeling  off  or  tearing,  such  as 
cannot  be  obtained  in  the  cold  bath  in  any  other  nickel  solu- 
tion ;  they  are  distinguished  by  great  homogeneity  and 
toughness. 

Conducting  salts.  To  decrease  the  resistance  of  the  nickel 
solutions,  conducting  salts  are  added  to  them,  which  are  also 
partially  decomposed  by  the  current.  Like  the  use  of  nickel 
chloride  in  nickeling  iron,  an  addition  of  ammonium  chloride,, 
which  is  much  liked,  cannot  be  recommended,  though  the 
subsequent  easy  deposition  of  nickel  with  a  comparatively 
weak  current  invites  its  employment. 

For  copper  and  its  alloys,  zinc,  etc.,  the  chlorine  combina- 
tions may  be  used,  but  for  nickeling  iron  they  must  be  avoided? 
as  the  source  of  future  evils. 

The  use  of  sodium  acetate,  barium  oxalate,  ammonium 
nitrate,  ammonium-alum,  etc.,  we  consider  unsuitable,  and 
partially  injurious,  and  are  of  the  opinion  that  with  few  ex- 
ceptions, which  will  be  referred  to  later  on,  potassium, 
sodium,  ammonia  or  magnesia  are  best  for  bases  of  the  con- 
ducting salts. 

The  effect  of  the  ions  separated  from  the  different  conduct- 
ing salts  varies  very  much  ;  the  potassium  ion  acts  different 
from  the  sodium  ion,  and  the  latter  different  from  the  mag- 
nesium ion,  and  an  idea  of  this  difference  in  action  of  the 
various  ions  can  be  formed  by  preparing,  according  to  formula 
VIII,  one  nickel  bath  with  potassium  citrate  and  another  with< 
sodium  citrate.  While  the  bath  prepared  with  the  potassium, 

*  German  patent,  No.  134,736. 


250  ELECTRO-DEPOSITION    OF    METALS. 

salt  works  quite  well  in  the  deeper  portions  on  zinc,  that  pre- 
pared with  the  sodium  salt  is  far  less  effective,  and  several 
other  proofs  derived  from  practice  could  be  mentioned.  An 
attempt  to  explain  these  facts  must  at  present  be  abstained 
from  as  this  suggestion  cannot  yet  be  proved  by  experiment  so 
that  no  objection  to  it  could  be  raised. 

Other  additions.— Some  other  additions  to  the  nickeling  bath 
which  are  claimed  to  effect  a  pure  silver-white  deposit  have 
been  recommended  by  various  experts.  Thus,  the  presence 
of  small  quantities  of  organic  acid  has  been  proposed  ;  for  in- 
stance, boric  acid  by  Weston,  ben  zoic  acid  by  Powell,  and 
citric  acid  or  acetic  acid  by  others.  The  presence  of  small 
quantities  of  free  acid  effects  without  doubt  the  reduction  of  a 
whiter  nickel  than  is  the  case  with  a  neutral  or  alkaline  solu- 
tion. Hence  a  slightly  acid  reaction  of  the  nickeling  bath,  due 
to  the  presence  of  citric  acid,  etc.,  with  the  exclusion  of  the 
strong  acids  of  the  metalloids,  can  be  highly  recommended. 
The  quantity  of  free  acid,  however,  must  not  be  too  large,  as 
this  would  cause  the  deposit  to  peel  off. 

Boric  acid  recommended  by  Weston  as  an  addition  to  nick- 
eling and  all  other  baths,  has  a  favorable  effect  upon  the  pure 
white  reduction  of  the  nickel,  especially  in  nickeling  rough 
castings,  i.  e.,  surfaces  not  ground.  Weston  claims  that  boric 
acid  prevents  the  formation  of  basic  nickel  combinations  on 
the  objects,  and  that  it  makes  the  deposit  of  nickel  more  ad- 
herent, softer,  and  more  flexible.  Whether  with  a  correct 
current-strength,  basic  nickel  salts,  to  which  the  yellowish 
tone  of  the  nickeling  is  said  to  be  due,  are  separated  on  the 
cathode,  is  not  yet  proved,  and  would  seem  more  than  doubt- 
ful. The  action  of  the  boric  acid  has  not  yet  been  scientific- 
ally explained,  but  numerous  experiments  have  shown  that 
the  deposition  of  nickel  from  nickel  solution  containing  boric 
acid  is  neither  more  adherent  nor  softer  and  more  flexible 
than  that  from  a  solution  containing  small  quantities  of  a  free 
organic  acid.  Just  the  reverse,  the  deposition  is  harder  and 
more  brittle  in  the  presence  of  boric  acid,  and  different  results 


DEPOSITION    OF    NICKEL    AND    COBALT.  251 

.may  very  likely  be  due  to  the  employment  of  varying  cur- 
rent-densities. 

In  view  of  the  fact  that  in  the  electrolysis  of  watery  solutions, 
water  also  takes  part  in  the  processes  enacted  on  the  electrodes, 
and  that  the  hydrogen  appearing  on  the  cathode  promotes  the 
formation  of  spongy,  pulverulent  and  dull  deposits,  Marino  * 
wants  to  substitute  glycerin  for  water.  Since  many  metallic 
salts  dissolve  only  to  a  slight  degree  in  glycerin,  the  content  of 
metal  in  a  glycerin  bath  is  very  low,  and  the  resistance  of  the 
cold  bath  so  great  that  enormous  voltages  are  needed  for  the 
separation  of  metals,  nickel,  for  instance,  requiring  more  than 
20  volts',  and  with  an  electro-motive  force  of  3  to  4  volts  de- 
posits can  only  be  produced  when  the  baths  have  been  heated 
to  quite  a  high  temperature.  However,  according  to  Foerster 
and  Langbein's  experiments,  the  deposits  do  not  possess  the 
good  qualities  claimed  by  the  patent,  and  cannot  be  forced 
to  such  thickness  as,  for  instance,  is  with  the  greatest  ease 
attained  in  nickel  ethyl-sulphate  baths. 

The  owners  of  the  Marino  patent  have  apparently  them- 
selves recognized  the  disadvantages  of  the  glycerin  electrolyte, 
and  have  applied  for  a  patent,  according  to  which  15  to  50  per 
-cent,  of  glycerin  is  to  be  added  to  solutions  of  metallic  salts  in 
water.  The  glycerin  is  claimed  to  act  as  depolarizer,  and  allow 
of  the  production  of  lustrous  nickel  deposits  of  great  homo- 
geneousness.  However,  the  correctness  of  these  statements 
may  be  doubted,  since  by  experiments  made  in  this  direction 
it  was  found  impossible  to  produce  a  better  technical  effect 
with  such  an  addition  of  glycerin  than  without  it,  in  properly- 
prepared  baths. 

It  may  here  again  be  emphasized  that  the  compositions  of 
the  electrolyte  must  vary  according  to  the  results  desired,  and 
that  it  is  impossible  to  attain  with  one  electrolyte  all  the  pos- 
sible properties  of  the  deposit. 

Moreover,  the  addition  of  glycerin  to  aqueous  electrolytes 

*  German  patent,  No.  104111. 


252  ELECTRO-DEPOSITION    OF    METALS. 

has  for  a  long  time  been  known  through  the  English  patents 
5300  and  22855,  and  it  might  be  supposed  that  if  such  an 
addition  were  of  special  advantage  it  would  have  long  ago 
come  into  general  use. 

Effect  of  current-density.  A  slighter  current-density  always 
and  under  all  conditions  causes  the  deposition  of  a  harder  and 
more  brittle  nickel  than  a  current  of  medium  strength,  while 
with  too  great  a  current-density,  the  metal  is  separated  in  pul- 
verulent form.  However,  as  will  be  shown  later  on,  nickel 
can  also  be  deposited  with  a  high  current-density  provided 
the  baths  are  of  proper  composition,  and  agitated. 

Electro-motive  force.  The  electro-motive  force  given  for  all 
the  baths  is  valid  for  the  normal  temperature  of  59°  to  64.4° 
F.  and  an  electrode-distance  of  10  cm.  It  has  previously 
been  mentioned,  that  with  an  increasing  temperature  of  the 
electrolyte  its  specific  resistance  becomes  less,  but  grows  as  the 
temperature  decreases,  less  electro-motive  force  being  required 
in  the  first  case,  and  more  in  the  latter. 

The  greater  the  electrode-distance  in  a  bath  is,  the  higher 
the  electro-motive  force  which  is  required.  A  statement  in 
figures  of  the  changes  in  electro-motive  force  for  the  various 
electrode-distances  will  not  be  given  because,  on  the  one  handr 
the  necessary  electro-motive  force  is  readily  determined  by  a 
practical  experiment,  and,  on  the  other,  a  calculation  in  ad- 
vance of  the  electro-motive  force  might  lead  to  wrong  con- 
clusions in  so  far  as  the  specific  resistance  of  the  electrolyte  is 
subject  to  change,  and  the  value  of  the  electro-motive  force  of 
the  counter  current  varies  very  much  for  the  objects  sus- 
pended as  cathodes,  according  to  the  nature  of  the  basis-metal 
of  which  they  are  composed.  For  this  reason  a  statement  of 
the  specific  resistances  of  the  bath  prepared  according  to  the 
directions  given  below  is  also  omitted,  because  such  state- 
ments would  be  valid  only  for  freshly-prepared  baths. 

Reaction  of  nickel  baths.  All  nickel  baths  work  best  when 
they  possess  a  neutral  or  slightly  acid  reaction.  Hence  blue 
litmus-paper  should  be  only  slightly  reddened,  and  red  congo 


DEPOSITION    OF    NICKEL    AND    COBALT.  253 

paper  must  not  be  changed  at  all.  Baths  prepared  with 
boric  acid  form  an  exception,  as  they  may  show  quite  a  strong 
acid  reaction.  An  alkaline  reaction  of  nickel  baths  is  abso- 
lutely detrimental,  such  baths  depositing  the  metal  dull  and 
with  a  yellowish  color,  and  do  not  yield  thick  deposits. 

Formulas  for  nickel  baths.  I.  The  most  simple  nickel  bath 
consists  of  a  solution  of  8  parts  by  weight  of  pure  nickel  am- 
monium sulphate  in  100  parts  by  weight  of  distilled  water. 

Electro-motive  force  at  10  cm.  electrode-distance,  3.0  volts. 

Current-density,  0.3  ampere. 

The  solution  is  prepared  by  boiling  the  salt  with  the  cor- 
responding quantity  of  water,  using  in  summer  10  parts  of 
nickel  salt  to  100  of  water,  but  in  winter  only  8  parts,  to  pre- 
vent the  nickel  salt  from  crystallizing  out.  This  bath,  which 
is  frequently  used,  possesses,  however,  a  considerable  degree 
of  resistance  to  conduction,  and  hence  requires  a  strong  cur- 
rent for  the  deposition  of  the  nickel.  It  als<5  requires  cast- 
nickel  anodes,  since  with  the  use  of  rolled  anodes  nickeling 
proceeds  in  a  very  sluggish  manner.  However,  the  cast 
anodes  rapidly  render  the  bath  alkaline,  necessitating  a  fre- 
quent correction  of  the  reaction.  The  alkalinity  is  overcome 
by  carefully  adding  dilute  sulphuric  or  citric  acid  to  neutral 
or  slightly  acid  reaction. 

To  decrease  the  resistance,  -recourse  has  been  had  to  certain 
conducting  salts,  and,  below,  the  more  common  nickel  baths 
will  be  discussed,  together  with  their  mode  of  preparation  and 
action,  as  well  as  their  availability  for  certain  purposes. 

II.  Nickel  ammonium  sulphate  17  ozs.,  ammonium  sul- 
phate 17  ozs.,  distilled  water  10  quarts. 

Electro-motive  force  at  10  cm.  electrode-distance,  1.8  to  2 
volts. 

Current-density,  0.35  ampere. 

Boil  the  salts  with  the  water,  and,  if  the  solution  is  too  acid, 
restore  its  neutrality  by  ammonia;  then  gradually  add  solution 
of  citric  acid  until  blue  litmus-paper  is  slowly  but  perceptibly 
reddened.  The  bath  deposits  rapidly,  it  possessing  but  little 


254  ELECTRO-DEPOSITION    OF    METALS. 

resistance,  and  all  metals  (zinc,  lead,  tin  and  Britannia,  after 
previous  coppering)  can  be  nickeled  in  it.  However,  upon 
rough  castings  and  iron,  a  pure  white  deposit  is  difficult  to 
obtain,  frequent  scratch-brushing  with  a  medium  hard-steel 
brush  being  required.  On  account  of  the  great  content  of 
sulphate  of  ammonium  in  the  bath,  the  nickel  deposit  piles  up 
especially  on  the  lower  portions  of  the  objects,  which,  in  con- 
sequence, readily  become  dull  (burn  or  over-nickel,  for  which 
see  later  on),  while  the  upper  portions  are  not  sufficiently 
nickeled.  For  this  reason  the  objects  must  be  frequently 
turned  in  the  bath  so  that  the  lower  portions  come  uppermost. 
This  piling-up  of  the  deposit  also  frequently  prevents  the 
latter  from  acquiring  a  uniform  thickness. 

III.  Nickel  ammonium  sulphate  25J  ozs.,  ammonium  sul- 
phate 8  ozs.,  crystallized  citric  acid  If  ozs.,  water  10  to  12 
quarts. 

Electro-motile  force  at  10  cm.  electrode-distance,  2.0  to  2.2 
volts. 

Current-density,  0.34  ampere. 

The  bath  is  prepared  in  the  same  manner  as  the  preceding, 
the  salts  being  dissolved  in  boiling  water,  and  ammonia  added 
until  blue  litmus  paper  is  only  slightly  reddened. 

This  bath  was  formerly  in  general  use  in  this  country  and 
is  to  some  extent  at  present  employed,  especially  for  nickeling 
ground  articles.  It  has  the  drawback  of  requiring  very  care- 
ful regulation  of  the  current  to  avoid  peeling  off.  According 
to  experiments  made  by  Dr.  Langbein,  it  would  be  better  to 
decrease  the  content  of  ammonium  sulphate  to  0.8  oz. 

The  reaction  of  this  bath  should  be  kept  only  very  slightly 
acid  or,  still  better,  neutral,  and  it  is  best  to  use  an  equal 
number  of  cast  and  rolled  nickel  anodes. 

If,  after  working  for  some  time,  the  objects  nickel  dark,  an 
addition  of  nickel  sulphate  is  advisable,  if  the  reaction  is  cor- 
rect and  possibly  not  alkaline. 

IV.  Nickel-ammonium  sulphate  23  ozs.,  ammonium  chlo- 
ride (crystallized)  11J  ozs.,  water  10  to  12  quarts. 


DEPOSITION    OF    NICKEL    AND    COBALT.  255 

Electro-motive  force  at  10  cm.  electrode-distance,  1.5  volts. 

Current-density,  0.55  ampere. 

The  bath  is  prepared  ,  in  the  same  manner  as  given  for  II 
and  III.  It  requires  exclusively  rolled  anodes,  nickels  very 
rapidly  and  quite  white,  but  the  deposit  is  soft  and  care  must 
therefore  be  had  in  polishing  upon  cloth  or  felt  bobs,  the 
corners  and  edges  of  the  objects  particularly  requiring  careful 
handling.  On  account  of  the  danger  of  peeling  off  a  heavy 
deposit  of  nickel  cannot  be  obtained  in  this  bath,  since,  in 
consequence  of  the  rapid  deposition  the  layer  of  nickel  con- 
denses and  absorbs  hydrogen,  is  formed  with  a  coarser 
structure  and  turns  out  less  uniform  and  dense.  These  phe- 
nomena are  a  hindrance  to  a  heavy  deposit  which,  if  it  is  to 
adhere,  must  be  homogeneous  and  dense. 

As  previously  mentioned,  baths  with  the  addition  of  chlorides, 
as  well  as  those  prepared  with  nickel  chloride  and  nickel  nitrate, 
are  not  suitable  for  the  solid  nickeling  of  iron.  They  are,  how- 
ever, well  adapted  to  the  rapid  light  nickeling  of  cheap  brass 
articles  on  which  no  great  demands  for  solidity  and  durability 
are  made.  To  obtain  nickeling  of  a  whiter  color,  only  7  ozs. 
in  place  of  11 J  ozs.  of  ammonium  chloride  and  3J  ozs.  of 
boric  acid  may  be  dissolved  with  the  assistance  of  heat.  The 
bath  then  requires  1.8  to  2  volts. 

V.  Nickel  chloride  (crystallized)  17  J  ozs.,  ammonium 
chloride  (crystallized)  17J  ozs.,  water  12  to  15  quarts. 

Electro-motive  force  at  10  cm.  electrode-distance,  1.75  to  2 
volts ;  for  zinc,  2.8  to  3  volts. 

Current-density,  0.5  ampere. 

This  bath  is  prepared  by  dissolving  the  salts  in  hike-warm 
water  and  adding  ammonia  until  the  bath  shows  a  very 
slightly  acid,  or  a  neutral,  reaction.  The  bath  deposits 
readily  and  is  especially  liked  for  nickeling  zinc  castings. 

All  the  drawbacks  of  the  preceding  bath  as  regards  the 
nickeling  of  iron  apply  also  to  this  bath,  only  to  a  still  greater 
extent.  Rolled  nickel  anodes  have  to  be  exclusively  used. 


'256  ELECTRO-DEPOSITION    OF    METALS. 

Nickel  Baths  Containing  Boric  Acid. 

VI.  Weston  recommends  the  following  composition  for 
"nickel  baths :  Nickel  chloride  17  J  ozs.,  boric  acid  7  ozs., 
water  20  quarts ;  or  nickel-ammonium  sulphate  35  ozs.,  boric 
acid  17  J  ozs.,  water  25  to  30  quarts.  Both  solutions  are  said 
to  be  improved  by  adding  caustic  potash  or  caustic  soda  so 
long  as  the  precipitate  formed  by  the  addition  dissolves. 

These  compositions,  however,  cannot  be  recommended,  be- 
•cause  the  baths  work  faultlessly  for  a  comparatively  short  time 
•only.  All  kinds  of  disturbing  phenomena  very  soon  made 
their  appearance,  the  deposit  being  no  longer  white  but  black- 
ish, and  the  baths  soon  failing  entirely.  Kaselowsky's  for- 
mula yields  similar  results.  This  bath  is  prepared  by  dissolv- 
ing, with  the  assistance  of  heat,  35|  ozs.  of  nickel-ammonium 
sulphate  and  17f  ozs.  of  boric  acid  in  20  quarts  of  water. 
This  bath  also  generally  fails  after  two  or  three  months'  use. 
The  cause -of  this  has  to  be  primarily  sought  for  in  the  fact 
that  baths  prepared  with  boric  acid  require,  according  to  their 
composition,  a  definite  proportion  between  rolled  and  cast 
nickel  anodes.  If  rolled  anodes  are  exclusively  used,  free 
sulphuric  acid  is  soon  formed,  which  causes  energetic  evolu- 
tion of  hydrogen  on  the  articles,  but  prevents  a  vigorous 
deposit  and  imparts  to  the  latter  a  tendency  to  peel  off.  The 
same  thing  happens  when  a  nickel  salt  not  entirely  neutral 
has  been  used  in  the  preparation  of  the  bath.  If,  on  the 
other  hand,  cast  nickel  anodes  alone  are  employed,  the  bath 
soon  becomes  alkaline,  with  turbidity  and  .the  formation  of 
slime,  and  the  deposit  turns  out  gray  and  dull  before  it  pos- 
sesses sufficient  thickness. 

From  the  foregoing  it  will  be  readily  understood  that  the 
nickel  salt  used  must  be  neutral,  and  that  the  proportion  of 
rolled  to  cast  anodes  must  be  so  chosen  that  the  free  sulphuric 
acid  formed  on  the  cast  anodes  is  neutralized,  but  that  the 
acidity  of  the  bath  dependent  on  the  free  boric  acid  is  con- 
stantly maintained. 


DEPOSITION    OF    NICKEL    AND    COBALT.  257 

A  recent  author  argues  in  support  of  Haber's  proposition 
that  the  effect  produced  by  the  use  of  mixed  anodes,  i.  e., 
rolled  and  cast  anodes,  might  be  attained  by  regulating  the 
•anode  current-density  by  the  use  of  definite  dimensions  of  the 
-anodes  in  such  a  way  that  the  electrolyte,  as  regards  its  com- 
position, remains  constant.  For  practical  purposes  this  would 
•only  be  feasible  without  trouble,  if  approximately  the  same 
•object-surface  is  always  present  in  the  bath,  otherwise  the 
maintenance  of  the  adequate  anode  current-density  must  be 
managed  by  taking  out  or  suspending  anodes  according  to 
the  varying  object-surfaces.  However,  this  is  far  more  trouble- 
some, and  the  use  of  mixed  anodes  is  decidedly  to  be  pre- 
ferred, it  having  been  shown  in  the  Galvanic  Institute  of  Dr. 
'George  Langbein,  that  by  this  means  the  reaction  of  a  bath 
can  for  years  be  kept  constant  even  with  considerable  varia- 
tions in  the  size  of  the  object-surface. 

Such  a  bath  containing  boric  acid  may  advantageously  be 
prepared  as  follows : 

VII.  Nickel-ammonium  sulphate  21  ozs.,  chemically  pure 
nickel  carbonate  If  ozs.,  chemically  pure  boric  acid  (crys- 
tallized) 10J  ozs.,  water  10  quarts. 

Electro-motive  force  at  10  cm.  electrode-distance,  2.25  to  2.5 
volts. 

Current-density,  0.35  ampere. 

Boil  the  nickel-ammonium  sulphate  and  the  nickel  carbon- 
ate *  in  the  water  until  the  evolution  of  bubbles  of  carbonic 
acid  ceases  and  blue  litmus-paper  is  no  longer  reddened. 
After  allowing  sufficient  time  for  settling,  decant  the  solution 
from  any  undissolved  nickel  carbonate,  and  add  the  boric 
acid.  Boil  the  whole  a  few  minutes  longer,  and  allow  to  cool. 
If  the  nickel  salt  contains  no  free  acid,  boiling  with  the  nickel 
carbonate  may  be  omitted.  The  solution  shows  a  strongly  acid 
-reaction,  which  must  not  be  removed  by  alkaline  additions. 

The  proportion  of  cast  to  rolled  anodes  used  in  this  bath  is 

*  In  place  of  nickel  carbonate,  nickel  hydrate  may  as  well  be  used. 

17 


258  ELECTRO-DEPOSITION    OF    METALS. 

dependent  on  the  quality  of  the  anodes.  The  use  of  readily- 
soluble  cast  anodes  requires  the  suspension  in  the  bath  of  more 
rolled  anodes  than  when  cast  anodes  dissolving  with  difficulty 
are  employed,  since  the  surfaces  of  the  latter,  in  consequence 
of  rapid  cooling,  are  not  readily  attacked.  The  proportion  has 
likewise  to  be  changed,  with  the  use  of  soft-  or  hard-rolled 
anodes.  Hence  the  proper  proportion  will  have  to  be  estab- 
lished by  frequently  testing  the  reaction  of  the  bath.  For  this 
purpose  the  following  rules  may  be  laid  down  :  Blue  litmus- 
paper  must  always  be  perceptibly  and  intensely  reddened,  but 
congo-paper  should  not  change  its  red  color,  for  if  the  latter 
turns  blue  it  is  an  indication  of  the  presence  of  free  sulphuric 
acid  in  the  bath,  which  has  to  be  neutralized  by  the  careful 
addition  of  solution  of  soda  or  potash  until  a  fresh  piece  of 
congo-paper  dipped  in  the  bath  remains  red.  Ammonia  can- 
not be  recommended  for  neutralizing  free  sulphuric  acid  in 
this  bath.  Red  litmus  paper  must  retain  its  color,  for  if  it 
turns  blue,  the  bath  has  become  alkaline,  and  fresh  boric  acid 
has  to  be  dissolved  in  the  previously  heated  bath  until  a  fresh 
piece  of  blue  litmus  paper  acquires  an  intense  red  color,  or 
pure  dilute  sulphuric  acid  has  to  be  added  to  the  bath,  stirring 
constantly,  until  blue  litmus  paper  is  reddened,  avoiding,  how- 
ever, an  excess  which  is  indicated  by  red  congo  paper  turning 
blue. 

This  bath  is  equally  well  adapted  for  nickeling  ground  ob- 
jects, as  well  as  for  rough  castings,  the  latter  acquiring  a  pure 
white  coating  of  nickel  if  thoroughly  scratch-brushed,  and  the 
bath  shows  a  normal  acid  reaction. 

Below  are  given  a  few  other  formulae  for  nickel  baths  which 
may  be  advantageously  used  for  special  purposes,  but  not  for 
nickeling  all  kinds  of  metals  with  equally  good  results. 

VIII.  Nickel  sulphate  10J  ozs.,  potassium  citrate  7  ozs., 
ammonium  chloride  7  ozs.,  water  10  to  12  quarts. 

For  copper  and  copper-alloys :  Electro-motive  force  at  10  cm. 
electrode-distance,  1.5  to  1.7  volts. 

Current-density,  0.45  to  0.5  ampere. 


DEPOSITION    OF    NICKEL    AND    COBALT.  259 

For  zinc :  Electro-motive  force  at  10  cm.  electrode-distance, 
2  to  2.5  volts. 

Current  density,  0.8  to  1  ampere. 

To  prepare  the  bath  dissolve  10J  ounces  of  nickel  sulphate 
and  3J  ounces  of  pure  crystallized  citric  acid  in  the  water ; 
neutralize  accurately  with  caustic  potash,  and  then  add  the 
ammonium  chloride.  This  bath  is  especially  adapted  for  the 
rapid  nickeling  of  polished,  slightly  coppered  zinc  articles, 
for  instance,  tops,  candlesticks,  mountings,  etc.  Deposition  is 
effected  with  a  very  feeble  current,  without  the  formation  of 
black  streaks,  such  as  are  otherwise  apt  to  appear  in  nickeling 
with  a  weak  current.  The  deposit  itself  is  dull  and  somewhat 
gray,  but  acquires  a  very  fine  polish  and  pure  white  color  by 
slight  manipulation  upon  the  polishing  wheels.  With  a 
stronger  current  the  bath  is  also  suitable  for  the  direct  nickel- 
ing of  zinc  articles;  it  must,  however,  be  kept  strictly  neutraL 
The  bath  works  with  rolled  anodes,  and  when  it  has  become 
alkaline,  requires  a  correction  of  the  reaction  by  citric  acid. 

IX.  Nickel  phosphate,  6J  ozs.,  sodium  pyrophosphate,  26f 
ozs.,  water,  10  quarts. 

For  copper  and  its  alloys :  Electro-motive  force,  at  10  cm., 
electrode-distance,  3.5  volts. 

Current  density,  0.5  ampere. 

For  the  preparation  of  the  nickel  phosphate  dissolve  12  ozs. 
of  nickel  sulphate  in  3  quarts  of  warm  water  and  10  ozs.  of 
sodium  phosphate  in  another  3  quarts  of  warm  water.  Mix 
the  two  solutions,  stirring  constantly,  and  filter  off  the  pre- 
cipitated nickel  phosphate. 

Dissolve  the  sodium  pyrophosphate  in  8  quarts  of  warm 
water,  add  the  nickel  phosphate,  which  soon  dissolves  by  thor- 
ough stirring,  and  make  up  the  bath  to  10  quarts  by  adding 
water. 

This  bath  yields  a  dark  nickeling  particularly  upon  sheet 
zinc  and  zinc  castings,  and  may  be  advantageously  used  for 
decorative  purposes  where  darker  tones  of  nickel  are  required. 
For  zinc,  work  with  3.8  volts  and  0.55  ampere. 


260  ELECTRO-DEPOSITION    OF    METALS. 

For  the  same  purpose  a  nickel  solution  compounded  with  a 
large  quantity  of  ammonia,  hence  an  ammoniacal  nickel 
solution  has  been  recommended.  However,  experiments  with 
this  solution  always  yielded  lighter  tones  than  bath  IX. 
Special  advantages  cannot  be  claimed  for  this  so-called  dark 
nickeling  since  in  arsenic  and  antimony  we  have  more  effective 
and  more  reliable  expedients. 

Black  nickeling.  Black  deposits  of  nickel  are  frequently 
used  particularly  for  decorative  purposes.  For  the  production 
of  such  deposits  general  directions  may  be  given  as  follows: 
1.  A  strong  bath  has  to  be  used.  2.  Apply  a  weak  current. 
For  the  production  of  a  uniform  black  deposit  the  current- 
strength  should  not  exceed  1  volt.  From  the  manner  in 
which  the  deposit  commences  to  form,  it  can  readily  be  recog- 
nized whether  the  current  is  of  suitable  strength.  The  first 
film  of  deposit  upon  the  object  is  iridescent,  i.  e.,  shows  rain- 
bow colors  and  does  not  extend  over  the  entire  surface.  The 
deposit  next  acquires  a  bluish  tone  until  finally  a  black  coat- 
ing is  formed.  If  the  deposit  acquires  immediately  in  the 
commencement  of  the  operation  a  uniform  color,  the  current 
is  too  strong.  The  deposit  should  form  slowly  ;  it  should,  as 
mentioned  above,  at  first  be  iridescent  and  the  black  deposit 
appear  only  after  one  or  two  minutes.  It  is  of  sufficient 
thickness  as  soon  as  the  desired  color  appears.  Very  thick 
deposits  are  apt  to  peel  off,  they  being  more  or  less  brittle. 
With  the  use  of  a  weak  current  30  to  60  minutes  will  be  re- 
quired for  the  production  of  a  deposit  of  sufficient  thickness. 
4.  A  large  number  of  nickel  anodes  should  be  used.  Old 
anodes  are  to  be  preferred,  they  yielding  nickel  more  readily 
than  new  ones.  5.  Any  acid  which  may  be  present  in  the 
bath  should  be  neutralized  by  the  addition  of  nickel  carbon- 
ate, a  neutral  bath  yielding  a  better  deposit  than  one  even 
only  slightly  acid. 

A  black  nickel  bath  of  the  following  composition  yields'  a 
very  uniform  black  deposit :  Water  4|  quarts,  double  sul- 
phate of  nickel  and  ammonium  10  ozs.,  ammonium  sulpho- 


DEPOSITION    OF    NICKEL    AND    COBALT.  261 

cyanate  1  oz.,  zinc  sulphate  1  oz.  This  bath  practically  con- 
tains exclusively  double  nickel  salts  which  dissolve  in  water. 
If  in  cold  weather  crystallizing  takes  place,  the  bath  has  to 
be  heated.  It  is  best  to  keep  the  temperature  of  the  bath  at 
from  70°  to  100°  F.;  at  a  higher  temperature  the  deposit 
readily  acquires  a  gray  color.  At  a  temperature  of  below 
59°  F.  some  nickel  salts  readily  crystallize  out,  and  besides 
the  bath  does  not  work  well. 

A  gray  color  of  the  deposit  is  an  indication  of  too  strong  a 
current,  this  being  also  the  case  when  streaks  are  formed  upon 
the  object.  With  the  use  of  an  old  bath  it  may  happen  that 
it  becomes  acid  and  it  will  be  noticed  that  a  black  coating  is 
not  produced,  even  by  reducing  the  current-strength.  The 
bath  then  very  likely  contains  free  acid,  and  the  best  means 
of  neutralizing  it  is  the  addition  of  nickel  carbonate.  In  case 
the  latter  is  not  available,  ammonia  may  be  used.  Test  the 
bath  with  litmus  paper.  If  before  adding  the  nickel  carbon- 
ate or  ammonia,  blue  limus  paper  when  dipped  into  the  bath 
turns  red,  the  bath  is  acid.  Add  nickel  carbonate  until  no 
more  of  it  dissolves,  although  a  small  excess  is  no  disadvan- 
tage. On  the  other  hand,  with  the  use  of  ammonia  care  must 
be  had  that  no  more  than  required  for  neutralization  is  added. 
When  the  limit  is  reached  at  which  the  color  of  either  blue 
or  red  litmus  paper  is  no  longer  changed,  no  more  ammonia 
should  be  added. 

Black  nickel  deposits  frequently  come  from  the  bath  with 
the  proper  black  color  and  otherwise  without  defect,  but  when 
rinsed  and  dried  have  a  brown  tone.  This  can  be  removed 
by  immersion  in  chloride  of  iron  solution.  The  latter  does 
not  attack  the  black  nickel  deposit,  provided  the  objects  are 
not  left  too  long  in  it,  a  moment's  immersion  being  sufficient, 
after  which  they  are  rinsed  and  dried.  The  chloride  of  iron 
bath  is  composed  of:  Chloride  of  iron  8J  ozs.,  hydrochloric 
acid  18  drachms,  water  4J  quarts. 

Black  nickel  deposits  when  exposed  to  the  influence  of 
atmospheric  air  gradually  acquire  a  brown  color  which,  how- 


262  ELECTRO-DEPOSITION    OF    METALS. 

ever,  is  only  superficial  and  can  be  wiped  off.  To  prevent 
such  tarnishing  a  coat  of  lacquer  is  as  a  rule  applied  to  the 
nickeled  object. 

Black  nickel  deposits  are  much  used  as  a  priming  in  the 
application  of  mat  black  lacquers  to  automobile  parts  and 
for  other  purposes,  where  as  durable  a  coating  as  possible  is 
desired.  If  the  lacquer  is  applied  without  previously  giving 
the  brass  a  suitable  black  nickel  deposit,  every  tiny  scratch  or 
peeling- off  becomes  perceptible,  which  is  prevented  by  the 
black  nickel  deposit  underneath  the  lacquer. 

A  black  nickel  bath  of  the  following  composition  has  been 
recommended  by  Blauet :  Water  95  gallons,  nickel-ammonium 
sulphate  12  ozs.,  potassium  sulphocyanide  2J  ozs.,  copper 
carbonate  2  ozs.,  arsenious  acid  2  ozs. 

Dissolve  the  nickel  salt  in  the  water  and  add  the  potassium 
sulphocyanide.  Then  dissolve,  at  about  176°  F.,  the  copper 
€arbonate  by  treatment  with  ammonium  carbonate  or  potas- 
sium cyanide,  and  add  the  solution,  while  lukewarm,  to  the 
bath.  Finally  add  the  arsenious  acid.  If  in  time  a  gray 
sediment  is  formed,  some  potassium  sulphocyanide  and  copper 
carbonate  have  to  be  added. 

X.  A  fairly  good  nickel  bath  for  many  purposes  is  obtained 
from  a  solution  of  nickel-ammonium  sulphate  22 J  ozs.,  mag- 
nesium sulphate  11J  ozs.,  water  10  to  12  quarts. 

For  iron  and  copper  alloys:  Electro-motive  force  at  10  cm. 
electrode-distance,  4  volts. 

Current-density,  0.2  ampere. 

t/  /  JT 

This  bath  deposits  with  ease,  and  a  heavy  coating  can  be 
produced  on  iron  without  fear  of  the  disagreeable  conse- 
quences of  bath  IV.  Even  zinc  may  be  directly  nickeled  in 
it  with  a  comparatively  feeble  current.  The  deposit,  how- 
ever, turns  out  rather  soft,  with  a  yellowish  tinge,  and  the 
bath  does  not  remain  constant,  but  fails  after  working  at  the 
utmost  three  or  four  months,  even  cast  anodes  being  but  little 
attacked. 

For  the  production  of  very  thick  deposits  a  bath  composed 


DEPOSITION    OF    NICKEL    AND    COBALT.  263 

of  nickel  sulphate  17.63  ozs.  and  sodium  citrate  17.63  ozs. 
dissolved  in  2f  .gallons  of  water  has  also  been  recommended. 
Pfanhauser  has  changed  these  proportions  to  nickel  sulphate 
14.11  ozs.  and  12.34  ozs.  sodium  citrate  dissolved  in  2f  gal- 
lons of  water.  This  bath  is  said  to  be  available  chiefly  for 
the  production  of  nickel  cliches  arid  thick  deposits.  It  has, 
however,  the  drawback  of  all  nickel  baths  prepared  with  large 
quantities  of  organic  combinations  of  requiring  a  high  electro- 
motive force  and  of  readily  becoming  mouldy.  It  can,  how- 
ever be  highly  recommended  for  nickeling  articles  with  sharp 
edges  and  points,  for  instance,  knives,  scissors,  etc.,  it  being 
quite  indifferent  towards  changes  in  the  current  proportions, 
so  that  even  with  a  higher  than  the  normal  electro-motive 
force  and  a  greater  current-density  the  objects  do  not  readily 
over-nickel.  The  deposit  is  very  soft,  and  hence  in  grinding 
such  nickeled  instruments  peeling-off  of  the  deposit  takes 
place  more  rarely  than  with  objects  nickeled  in  baths  of  dif- 
ferent composition.  Electro-motile  force  at  10  cm.  electrode- 
distance,  3  volts  ;  current-density,  0.35  ampere. 

According  to  an  English  formula,  17.63  ozs.  nickel  sulphate, 
9  ozs.  5J  drachms  tartaric  acid  and  2.4  ozs.  caustic  potash  are 
dissolved  in  2f  gallons  of  water.  The  results  with  this  bath 
were  only  moderate. 

It  has  not  been  deemed  necessary  to  give  additional  form- 
ulas for  nickel  baths,  because  no  better  results  were  obtained 
from  other  receipts  which  have  been  published  and  which 
have  been  thoroughly  tested,  than  from  those  given  above. 
In  most  cases  success  with  them  fell  far  short  of  expectation. 

Some  authors  have  recommended  for  nickeling  a  solution 
of  nickel  cyanide  in  potassium  cyanide,  but  experiments 
failed  to  obtain  a  proper  deposition  of  nickel. 

The  addition  of  carbon  disulphide  to  nickel  baths,  which 
has  been  recommended  by  Bruce,  is  not  advisable.  Accord- 
ing to  Bruce,  such  an  addition  prevents  the  nickel  deposit 
from  becoming  dull  when  reaching  a  certain  thickness,  but 
repeated  experiments  made  strictly  in  accordance  with  the 
directions  given  did  not  confirm  this  statement. 


264  ELECTRO-DEPOSITION    OP    METALS. 

The  general  remark  may  here  be  added  that  freshly  pre- 
pared nickel  baths  mostly  work  correctly  from  the  start,, 
though  it  may  sometimes  happen  that  the  articles  first  nickeled 
come  from  the  bath  with  a  somewhat  darker  tone.  In  this 
case  suspend  a  few  strips  of  iron  or  brass-sheet  to  the  object- 
rod;  allow  the  bath  to  work  for  one  or  two  hours,  when 
nickeling  will  proceed  faultlessly.  If,  however,  such  should 
not  be  the  case,  ascertain  by  a  test  with  the  hydrometer 
whether  the  specific  gravity  of  the  bath  is  too  high.  If  the 
deposit  does  not  turn  out  light,  even  after  dilution,  it  is  very 
likely  that  the  nickel  salt  contains  more  than  traces  of  copper, 
or,  with  black-streaked  nickeling,  zinc. 

It  has  also  been  observed  that  the  deposit  frequently  peels 
off  when,  for  the  purpose  of  neutralization,  additions  have 
been  made  to  the  nickel  baths.  This  phenomenon  disappears- 
in  a  few  days,  but  it  demonstrates  that,  instead  of  correcting 
the  reaction  of  the  bath  by  the  addition  of  acids  or  alkalies,  it 
should  be  done  by  increasing  the  rolled  anodes  in  case  the 
bath  shows  a  tendency  to  become  alkaline,  or  to  increase  the 
cast  anodes  in  case  the  bath  becomes  too  acid. 

A  few  words  may  here  be  said  in  regard  to  what  may  be 
termed  a  nickel  bath  without  nickel  salt.  It  simply  consists  of 
a  15  to  20  per  cent,  solution  of  ammonium  chloride,  which 
transfers  the  nickel  from  the  anodes  to  the  articles.  Cast 
anodes  are  almost  exclusively  used  for  the  purpose,  and  depo- 
sition may  be  effected  with  quite  a  feeble  current.  Before 
the  solution  acquires  the  capacity  of  depositing,  quite  a  strong 
current  has  to  be  conducted  through  the  bath  until  the  com- 
mencement of  a  proper  reduction  of  nickel.  This  bath  is 
only  suitable  for  coloring  very  cheap  articles,  it  being  impos- 
sible to  produce  solid  nickeling  with  it.  It  is  here  mentioned 
because  it  may  serve  as  a  representative  of  a  series  of  other 
electro-plating  baths  in  which  the  transfer  of  the  metal  is 
effected  by  ammonium  chloride  solution  without  the  use  of 
metallic  salts,  for  instance,  iron,  zinc,  cobalt,  etc. 

Prepared  nickel  salts.     As  previously  mentioned,  there  is  a 


DEPOSITION    OF    NICKEL    AND    COBALT.  265 

large  number  of  receipts  for  nickel  baths,  some  of  them  being 
entirely  unsuitable,  while  others  are  only  available  for  certain 
purposes.  Hence,  it  is  impossible,  even  for  the  skilled  oper- 
ator, to  separate  the  good  receipts  from  the  bad  ones,  if  he  is 
not  qualified  to  do  so  by  many  years'  experience  and  a  thor- 
ough knowledge  of  chemistry.  The  choice  is  still  more  diffi- 
cult for  the  beginner  and  layman,  and  it  is  recommended  to 
them  to  get  their  supply  of  suitable  baths  from  well-known 
dealers  in  electro-plating  supplies. 

By  prepared  nickel  salts  are  understood  preparations  which, 
in  addition  to  the  most  suitable  nickel  salt,  contain  the  re- 
quired conducting  salt  for  the  decrease  of  the  resistance,  and 
further  such  additions  as  promote  a  pure  white  separation  of 
nickel,  and  are  necessary  for  the  continuously  good  working 
of  the  bath. 

Correction  of  the  reaction  of  nickel  baths.  When  after  long 
use  a  nickel  bath  has  become  alkaline,  which  is  readily  deter- 
mined by  a  test  with  litmus  paper,  this  defect  can  in  a  few 
minutes  be  overcome  by  the  addition  of  an  acid,  and  accord- 
ing to  the  composition  of  the  bath,  its  neutrality  or  slightly 
acid  reaction  can  be  restored  by  citric,  acetic,  sulphuric,  boric 
acids,  etc.  The  use  of  hydrochloric  acid  for  this  purpose, 
which  has  been  recommended,  is  not  advisable.  In  most 
cases  it  will  be  best  to  employ  dilute  sulphuric  acid,  provided 
an  excess  of  it  be  avoided,  which  is  recognized  by  red  congo- 
paper  turning  blue. 

When  a  bath  contains  too  much  free  acid,  the  latter  may  be 
removed  by  an  addition  of  ammonia,  ammonium  carbonate, 
potash  or  nickel  carbonate,  the  choice  of  the  agent  to  be  used 
depending  on  the  composition  of  the  bath. 

Thick  deposits  in  hot  nickel  baths.  Nickel  baths,  more  or  les& 
highly  heated,  have  for  years  been  used  for  nickeling,  the 
purpose  being,  on  the  one  hand,  the  production  in  a  shorter 
time  of  a  thick  deposit,  and  on  the  other,  it  was  expected  that 
the  product  thus  obtained  would  become  especially  dense  in 
consequence  of  the  contraction  in  cooling. 


:266  ELECTRO-DEPOSITION    OF    METALS. 

The  results  obtained  in  heated  baths  were,  however,  un- 
satisfactory, since,  if  the  current  was  not  carefully  regulated, 
the  deposit  peeled  off  readily,  and  the  polished  nickeling 
became  dull  on  exposure  to  the  air. 

The  unsatisfactory  results  might  primarily  have  been  due 
to  an  unsuitable  composition  of  the  electrolytes.  Foersters's  * 
experiments  have  shown  that  almost  perfectly  smooth  de- 
posits of  0.5  to  1  millimeter  thickness  may  be  obtained  in 
absolutely  neutral  nickel  solutions  with  a  high  content  of 
nickel— 1  oz.  or  more  per  quart — if  kept  at  a  temperature  of 
122°  to  194°  F.,  for  instance,  in  solutions  containing  5  ozs. 
-nickel  sulphate  per  quart,  at  167°  to  176°  F.  Electro-motive 
force,  at  an  electrode-distance  of  4  cm.,  1.3  volts;  current- 
density,  2  to  2.5  amperes. 

Exhaustive  experiments  made  by  Dr.  George  Langbein  led 
to  the  result  that  deposits  of  great  thickness  may  also  be  pro- 
duced in  slightly  acidulated  nickel  baths  of  suitable  composi- 
tion, at  a  temperature  kept  constant  at  from  185°  to  194°  F. 
In  a  bath  which  contained  12.34  ozs.  of  nickel  sulphate  and 
6.34  ozs.  of  sodium  sulphate  or  magnesium  sulphate  per 
quart,  and  which  was  slightly  acidulated  with  acetic  acid, 
deposits  of  0.5  millimeter  thickness  were  in  12  hours  obtained, 
the  current-density  amounting  to  4  amperes. 

For  nickeling  flat  objects  the  current-density  may,  however, 
be  materially  increased,  one  of  up  to  8  amperes  or  more  being 
permissible.  By  reason  of  the  rapidity  with  which  thick  de- 
posits can  be  produced  in  hot  baths  of  the  above-mentioned 
composition,  the  term  quick  nickeling  has  been  applied  to  this 
process. 

Independent  of  Dr.  Langbein,  Dr.  Kugel  discovered  that 
thick  deposits  of  nickel  can  be  obtained  in  a  hot  nickel  bath 
of  nickel  sulphate  and  magnesium  sulphate  very  slightly 
-acidulated  with  sulphuric  acid.f 

*  Zeitschrift  fur  Elektrochemie,  1897  to  1898,  p.  160. 
f  German  patent,  117054. 


DEPOSITION    OF    NICKEL    AND    COBALT.  267 

While,  in  order  to  avoid  the  formation  of  roughness  and 
bud-like  excrescences,  Foerster  found  agitation  of  the  electro- 
lytes, of  the  composition  mentioned  by  him  of  advantage,  Dr. 
Langbein  obtained  smoother  deposits  when  the  electrolyte  was 
not  mechanically  agitated,  and  the  fluid  was  only  slowly  mixed 
through  by  heating  with  a  steam  coil. 

Upon  flat  objects,  for  instance,  sheets,  very  uniform  deposits 
1  millimeter  or  more  in  thickness  are  very  rapidly  obtained,  as 
well  as  upon  round  objects,  if  care  be  taken  to  have,  by  the 
use  of  anodes  of  the  same  shape,  a  uniform  anode-distance 
from  all  object  surfaces.  However,  the  production  of  such 
deposits  of  entirely  uniform  thickness  upon  articles  with  high 
relief  has  thus  far  not  been  successfully  accomplished  by  Dr. 
Langbein  with  the  use  of  the  above-mentioned  electrolytes. 

Thick  deposits  in  cold  nickel  baths.  By  the  use  of  an  electro- 
lyte which  contains  nickel  ethyl  sulphate  (German  patent, 
No.  134736)  or  the  ethyl  sulphates  of  the  alkalies  or  alkaline 
earths,  deposits  of  any  desired  thickness  can  be  produced  if 
the  bath  be  constantly  agitated  by  mechanical  means  or  the 
introduction  of  hydrogen.  Agitation  by  blowing  in  air  is  not 
permissible  on  account  of  oxidation  of  the  ethyl-sulphate 
•combinations  by  the  oxygen  of  the  air. 

Continued  experiments  with  such  ethyl-sulphate  combina- 
tions by  Dr.  G.  Langbein  &  Co.  resulted  in  finding  formulas 
for  prepared  nickel  salts  from  the  solutions  of  which  thick  de- 
posits of  nickel  capable  of  being  polished  can  in  a  few  minutes 
be  obtained  in  the  cold  way.  The  formulas  for  these  different 
prepared  nickel  salts  will  not  be  given,  as  they  are  protected 
by  patents.  The  salts  are  known  in  commerce  as  Mars, 
Lipsia,  Germania  and  Neptune. 

In  an  electrolyte  of  given  composition,  which  has  to  be 
constantly  kept  slightly  acid  with  acetic  acid,  nickeling  may 
for  weeks  be  carried  on  at  the  ordinary  temperature  without 
any  peeling-off  of  the  deposit  being  noticed,  and,  in  this 
respect,  this  bath  surpasses  all  other  known  baths.  In  the 
course  of  six  weeks,  Dr.  Langbein  has  produced  upon  gutta- 


268  ELECTRO-DEPOSITION    OF   METALS. 

percha  matrices,  galvanoplastic  nickel  deposits  6  millimeters 
in  thickness,  the  metal  proving  thoroughly  homogeneous  and 
firmly  united  throughout  its  entire  thickness. 

Coehn  and  Siemens  *  found  that  from  electrolytes  which 
contain  nickel  salts  and  magnesium  salts,  weighable  quantities 
of  magnesium  are  under  certain  conditions  separated  together 
with  the  nickel,  and  they  succeeded  in  depositing  alloys  con- 
taining approximately  90  per  cent,  of  nickel  and  10  per  cent, 
of  magnesium.  According  to  the  above-mentioned  authors, 
the  behavior  of  the  nickel-magnesium  alloys  in  the  electrolytic 
separation  differs  essentially  from  that  of  nickel,  they  showing 
especially  no  tendency  towards  peeling  off. 

Nickel  anodes.  Either  cast  or  rolled  nickel  plates  are  used 
as  anodes,  they,  of  jcourse,  having  to  be  made  of  the  purest 
quality  of  nickel.  Every  impurity  of  the  anode  passes  into  the 
bath,  and  jeopardizes,  if  not  at  first,  then  finally,  its  successful 
working.  Rolled  anodes  dissolve  with  difficulty  and  cast 
anodes,  as  a  rule,  with  ease.  If  the  latter  dissolve  only  with 
difficulty  they  fail  in  their  object  of  replacing  the  nickel  metal 
withdrawn  from  the  bath  by  the  nickeling  process. 

As  regards  solubility,  electrolytically  produced  nickel  anodes 
stand  between  rolled  and  cast  anodes. 

The  anodes  should  not  be  too  thin,  otherwise  they  increase 
the  resistance.  For  small  baths  rolled  anodes  2  to  3  milli- 
meters thick  are  generally  used.  For  larger  baths,  it  is  better 
to  use  plates  3  to  10  millimeters  thick,  while  the  thickness  of 
cast  anodes  may  vary  from  3  to  10  millimeters,  according  to 
their  size. 

Attention  may  here  be  called  to  the  elliptic  anodes,  Fig. 
110,  patented  by  the  Hanson  &  Van  Winkle  Co.,  Newark, 
N.  J.  The  great  advantage  claimed  in  the  use  of  these 
elliptic  anodes  over  the  old  style  flat  plate  is  the  uniformity 
of  deposit  as  disintegration  takes  place  from  all  sides  of  tha 
anode ;  consequently  the  molecules  are  distributed  uniformly 

*Zeitsctmft  fur  Elektrochemie,  1902,  S.  591. 


DEPOSITION    OF    NICKEL    AND    COBALT. 


269 


FIG.  110. 


throughout  the  solution,  and  not  only  hasten  the  deposit,  but 
give  a  heavier  deposit  in  a  given  time.  Another  important 
feature  in  these  anodes  is 
the  fact  that  they  wear 
down  evenly  to  a  small, 
narrow  strip,  and  when 
worn  down  to  such  a 
point  that  it  seems  de- 
sirable to  put  in  more 
nickel,  the  old  ones  which 
take  up  practically  no 
room  in  the  tank,  can  re- 
main until  entirely  con- 
sumed, and  as  a  result 
there  is  practically  no 
scrap  nickel  to  dispose  of 
at  half  price.  Fig.  Ill 
shows  the  small  loss  in 
the  use  of  the  elliptic 
.anode.  The  weight  of 
the  orginal  plate  was  16 
pounds.  Percentage  of 
waste  only  5  per  cent. 

Fig.  112  shows  the  or- 
iginal shape  of  the  flat 
plate  still  largely  used 
and  the  character  of  the 
wear.  The  top  part  of 
the  scrap-plate  with  its 
two  ears  is  almost  as 
heavy  as  the  same  section 
of  the  original  plate.  The 
original  weight  of  the 
plate  was  13|  Ibs.  Waste 

2  Ibs.     Percentage  of  waste  14.6  per  cent.     Another  form  of 
the  old-style  plate  is  shown  in  Fig.  113.     The  original  weight 


270 


ELECTRO-DEPOSITION    OF    METALS. 


was  17J  Ibs.     Weight  of  scrap  4J  Ibs.     Percentage  of  waste 
27.4  per  cent.     The  examples  shown  in  the  illustrations  were 


FIG.  111. 


mrtti 


10  o±. 


if  bz 


12  oz 


14  OZ. 


13  oz,      I0 


16   LBS 


taken  from  a  lot  of  scrap  returned  to  the  manufacturers.     The 
scrap  from  the  elliptic  anode  came  from  a  large  stove  concern 


FIG.  112. 


FIG.  113. 


and  the  flat  scrap  also  from  a  stove  manufacturer.     Elliptic 
anodes  are  furnished  in  all  commercial  metals. 


DEPOSITION    OF    NICKEL    AND    COBALT.  271 

The  use  of  insoluble  anodes  of  retort  carbon  or  platinum, 
either  by  themselves  or  in  conjunction  with  nickel  anodes,  as 
frequently  recommended  by  theorists,  is  not  advisable.  The 
harder  and  the  less  porous  the  nickel  anode  is,  the  less  it  is 
attacked  in  the  bath  and  the  less  it  fulfills  the  object  of  keeping 
constant  the  metallic  content  of  the  solution.  On  the  other 
hand,  the  softer  and  the  more  porous  the  anode  is,  the  more 
readily  it  dissolves,  because  it  conducts  the  current  better  and 
presents  more  points  of  attack  to  the  bath ;  and  the  more  it  is 
dissolved,  the  more  metal  is  conveyed  to  the  bath.  With  the 
sole  use  of  rolled  anodes  and  working  with  a  feeble  current, 
free  acid  is  formed  in  the  bath;  on  the  other  hand,  by  working 
with  cast  anodes  alone,  the  bath  readily  becomes  alkaline. 
Now  it  would  appear  that  the  possibility  of  a  bath  also  becom- 
ing alkaline  even  with  the  sole  use  of  rolled  anodes,  especially 
when  working  with  a  strong  current,  has  led  to  the  proposition- 
of  suspending  in  the  bath,  besides  the  nickel  anodes,  a  suffi- 
cient number  of  insoluble  anodes  in  order  to  effect  a  constant 
neutrality  of  the  bath.  It  would  lead  too  far  to  go  into  the 
theory  of  the  secondary  decompositions  which  take  place  in  a 
nickel  bath  to  prove  that,  though  neutrality  is  obtained,  it  can 
only  be  done  at  the  expense  of  the  metallic  content  of  the 
bath.  Hence  this  impracticable  proposition  will  here  be  over- 
thrown by  practical  reasons,  it  only  requiring  to  be  demon- 
strated that  in  baths  becoming  alkaline  the  content  of  nickel 
also  decreases  steadily  though  slowly.  This  fact  in  itself  shows 
that  in  order  to  save  the  occasional  slight  labor  of  neutralizing 
the  bath,  the  decrease  of  the  metallic  content  should  not  be 
accelerated  by  the  use  of  insoluble  anodes. 

For  larger  baths  the  use  of  expensive  platinum  anodes  as 
insoluble  anodes  need  not  be  taken  into  consideration,  be- 
cause for  large  surfaces  of  objects  correspondingly  large  sur- 
faces of  platinum  anodes  would  have  to  be  present,  as  other- 
wise the  resistance  of  thin  platinum  sheets  would  be  consider- 
able. But  such  an  expensive  arrangement  would  be  justifiable 
only  if  actual  advantages  were  obtained,  which  is  not  the 


272  ELECTRO-DEPOSITION    OF    METALS. 

•case,  because,  though  the  platinum  does  absolutely  not  dis- 
solve, the  deficiency  of  metallic  nickel  in  the  bath  caused' by 
such  anodes  must  in  some  manner  be  replaced. 

The  insoluble  anodes  of  gas-carbon,  which  have  frequently 
been  proposed,  are  attacked  by  the  bath.  Particles  of  carbon 
become  constantly  detached,  and  floating  upon  the  bath,  de- 
posit themselves  upon  the  objects  and  cause  the  layer  of 
nickel  to  peel  off.  Furthermore,  by  the  use  of  nickel  anodes 
in  conjunction  with  carbon  anodes,  the  current,  on  account  of 
the  greater  resistance  of  the  latter,  is  forced  to  preferably  take 
its  course  through  the  metallic  anodes,  in  consequence  of 
which  the  articles  opposite  the  nickel  anodes  are  more  thickly 
nickeled  than  those  under  the  influence  of  the  carbon  anodes. 
With  larger  objects  this  inequality  in  the  thickness  of  the  de- 
posit is  again  a  hindrance  to  obtaining  layers  of  good  and 
uniform  thickness,  such  as  are  required  for  solid  nickeling. 
Since  the  current  preferably  seeks  its  compensation  through 
these  separate  metallic  anodes,  they  are  more  vigorously 
attacked  than  when  nickel  plates  only  are  suspended  in  the 
bath. 

With  nickel  baths  which  contain  a  considerable  amount  of 
ammonium  chloride,  the  use  of  a  few  carbon  anodes  along  with 
the  rolled  nickel  anodes  may  be  permissible,  since  these  baths 
strongly  attack  even  the  rolled  anodes,  and  thereby  convey  to 
ihe  bath  sufficient  quantities  of  fresh  nickel.  Such  baths  con- 
taining ammonium  chloride,  as  a  rule,  become  very  rapidly 
alkaline,  so  that  frequent  neutralization  becomes  inconvenient. 
However,  in  this  case,  it  is  advisable  to  place  the  carbon 
anodes  in  small  linen  bags  which  retain  any  particles  of  car- 
bon becoming  detached,  the  latter  being  thus  prevented  from 
depositing  upon  the  articles  in  the  bath. 

According  to  long  practical  experience,  the  best  plan  is  to 
•use  rolled  and  cast  anodes  together  in  a  bath  which  does  not 
•contain  chlorides,  and  to  apportion  the  anode  surface  so  that 
an  anode-rod,  about  f  of  its  length,  is  fitted  with  anodes.  If, 
for  instance,  a  tank  is  120  centimeters  long  in  the  clear  and  50 


DEPOSITION    OF    NICKEL    AND    COBALT.  273 

•centimeters  deep,  the  width  of  the  nickel  anodes  laid  alongside 
one  another  should  be  about  80  centimeters,  and  their  length 
about  |  of  the  depth  of  the  tank,  hence  30  centimeters.  For 
•each  anode-rod,  8  anodes,  each  30  centimeters  long  and  10 
centimeters  wide,  would,  therefore,  be  required. 

The  proportion  of  cast  to  rolled  anodes  depends  on  the  com- 
position of  the  bath,  but  it  may  be  laid  down  as  a  rule  that 
baths  with  greater  resistance  require  more  cast  anodes,  and 
baths  with  less  resistance  more  rolled  anodes.  Baths  with  the 
greatest  resistance,  for  instance,  that  prepared  according  to 
formula  I,  require  only  cast  anodes,  while  baths  with  the 
smallest  resistance,  for  instance,  those  containing  ammonium 
chloride,  may  to  advantage  work  only  with  rolled  anodes  ; 
baths  with  medium  resistance  require  mixed  anodes. 

The  proper  proportion  has  been  established  when,  after  work- 
ing for  some  time,  the  original  reaction  of  the  bath  remains  as 
constant  as  possible.  When  the  bath  is  observed  to  become 
alkaline,  the  number  of  rolled  anodes  should  be  increased,  but 
when  the  content  of  acid  increases  they  should  be  decreased, 
and  the  number  of  cast  anodes  increased. 

Cast  anodes,  especially  those  not  cast  very  hot,  have,  to  be 
sure,  the  disadvantage  of  becoming  brittle,  and  crumbling 
before  they  are  entirely  consumed.  Nickel  anodes  cast  in  iron 
moulds  are  so  hard  on  their  surfaces  as  to  resist  the  action  of 
the  bath,  and  dissolve  only  with  difficulty,  so  that  the  con- 
tent of  metal  of  the  bath  is  only  incompletely  replenished. 
Anodes  cast  in  sand  moulds,  and  slowly  cooled,  are  porous 
and  consequently  dissolve  readily,  but  by  reason  of  their  por- 
osity their  interior  portions  are  also  attacked.  If  such  an 
anode  be  broken,  it  will  be  found  that  the  interior  contains  a 
black  powder  (nickel  oxide)  which  novices  sometimes  believe 
to  be  carbon.  In  fact  cases  have  been  heard  of  that  customers 
have  complained  that  the  anodes  furnished  them  were  not 
nickel  anodes  at  all,  but  simply  carbon  plates  coated  with  a 
layer  of  nickel. 

The  cast  anodes  suspended  to  the  ends  of  the  conducting 
18 


274  ELECTRO-DEPOSITION    OF    METALS. 

rods  are  especially  strongly  attacked,  and,  therefore,  when 
rolled  and  cast  anodes  are  used  together,  it  is  best  to  suspend 
the  latter  more  towards  the  center,  and  the  former  on  the  ends 
of  the  rods. 

These  drawbacks,  however,  are  not  sufficient  to  prevent 
the  use  of  a  combination  of  cast  and  rolled  anodes  when  re- 
quired by  the  composition  of  the  bath.  The  brittle  remnants- 
of  the  anodes  are  thoroughly  washed  in  hot  water,  dried,  and 
sold. 

Rolled  nickel  anodes  are  less  liable  to  corrosion,  and  may  be 
used  up  to  the  thickness  of  a  sheet  of  paper  before  they  fall  to 
pieces.  It  is,  however,  best  to  replace  them  by  fresh  anodes 
before  they  become  too  thin,  since  with  the  decrease  in  thick- 
ness  their  resistance  increases. 

It  is  best  to  allow  the  anodes  to  remain  quietly  in  the  bath, 
even  when  the  latter  is  not  in  use,  they  being  in  this  case  not 
attacked.  By  frequently  removing  and  replacing  them  they 
are  subject  to  concussion,  in  consequence  of  which  they 
crumble  much  more  quickly  than  when  remaining  quietly  in 
the  bath. 

In  the  morning,  before  nickeling  is  commenced,  the  anodes 
will  frequently  show  a  reddish  tinge,  which  is  generally 
ascribed  to  a  content  of  copper  in  the  bath  or  in  the  anodes. 
This  reddish  coloration  also  appears  when  an  analysis  shows 
the  anodes,  as  well  as  the  bath,  to  be  absolutely  free  from  cop- 
per. It  is  very  likely  due  to  a  small  content  of  cobalt,  from 
which  nickel  anodes  can  never  be  entirely  freed.  It  would 
seem  that  by  the  action  of  a  feeble  current,  cobaltous  hydrate 
is  formed,  which,  however,  immediately  disappears  on  con- 
ducting a  strong  current  through  the  bath. 

Pfanhauser  is  of  the  opinion  that  this  reddish  tinge  is  due 
to  a  separation  of  copper.  In  fact,  even  the  purest  brands  of 
anodes  contain  traces  of  copper,  but,  on  the  other  hand,  the 
nickel  salts  are  at  present  furnished  mostly  entirely  free  from 
copper,  and  a  nickel  bath  would  have  to  be  worked  for  a  long 
time  before  a  content  of  copper  would  be  transferred  to  it  from 


DEPOSITION    OF    NICKEL    AND    COBALT.  275 

the  anodes.  An  experiment  showed  that  a  bath  prepared 
with  nickel  salt  absolutely  free  from  copper  produced  a  slight 
red  film  upon  a  new  anode  without  the  current  having  been 
in  action  ;  a  bright  steel-sheet  served  as  anode.  This  does 
not  indicate  the  separation  of  copper,  as  its  derivation  would 
in  this  case  be  inexplicable. 

The  anodes  are  supported  by  pure  nickel  wire  0.11  to  0.19 
inch  thick,  or  by  strips  of  nickel  sheet  riveted  on. 

It  has  previously  been  mentioned  that  the  anodes  in  baths 
at  rest  are  frequently  more  strongly  attached  at  the  upper  than 
at  the  lower  portions,  because  specifically  lighter  layers  of  fluid 
are  present  on  top  and  heavier  ones  below,  and  the  current 
takes  the  road  where  there  is  the  least  resistance.  This  dis- 
proportionate solution  of  the  anodes  may,  however,  also  be 
noticed  in  baths  which  are  agitated,  and  consequently  in  which 
no  layers  of  different  specific  gravities  are  present.  The  lower 
and  side  edges  will  be  found  more  corroded  than  the  middle 
portions  of  the  anodes,  and  the  backs,  opposite  to  which  no 
objects  are  suspended  appear  also  strongly  attacked.  These 
observations  render  plausible  Pfanhauser's  supposition  that  the 
current  does  not  in  all  places  migrate  directly  and  in  straight 
lines  from  the  anodes  to  the  cathodes,  but  that,  as  with  the 
magnetic  lines  of  force,  this  migration  takes  place  in  curves, 
especially  when  the  anode-surface  is  small  in  proportion  to  the 
cathode-surface.  Pfanhauser  has  applied  the  term  scattering' 
of  current  lines  to  this  migration  of  the  current  in  curves,  and 
has  noticed  that  it  grows  with  the  electrode-distance,  and 
decreases  as  the  electro-surfaces  are  increased. 

Execution  of  nickeling.  Next  to  the  correct  composition  of 
the  bath  and  the  proper  selection  of  the  anodes,  the  success 
of  the  nickeling  process  depends  on  the  articles  having  been 
carefully  freed  from  grease  and  cleaned,  and  on  the  correct 
current-strength. 

The  mechanical  preparation  of  the  objects  has  been  dis- 
cussed on  page  188  et  seq. 

The  directions  for  the  removal  of  grease,  etc.,  given  on  p. 


276  ELECTRO-DEPOSITION    OF    METALS. 

228,  also  apply  to  objects  to  be  nickeled.  In  executing  the 
operations,  it  should  always  be  borne  in  mind  that  though 
dirty,  greasy  parts  become  coated  with  nickel,  the  deposit  im- 
mediately peels  off  by  polishing,  because  an  intimate  union 
of  the  deposit  with  the  basis-metal  is  effected  with  only  per- 
fectly clean  surfaces.  Touching  the  cleansed  articles  with  the 
dry  hand  or  with  dirty  hands  must  be  strictly  avoided  ;  but, 
if  large  and  heavy  objects  have  to  be  handled,  the  hands 
should  first  be  freed  from  grease  by  brushing  with  lime  and 
rinsing  in  water,  and  be  kept  wet. 

As  previously  mentioned,  the  cleansed  objects  must  not  be 
exposed  to  the  air,  but  immediately  placed  in  the  bath,  or,  if 
this  is  not  practicable,  be  kept  under  clean  water. 

While  copper  and  its  alloys  (brass,  bronze,  tombac,  Ger- 
man silver,  etc.),  as  well  as  iron  and  steel,  are  directly  nick- 
eled, zinc,  tin,  Britania  and  lead  are  generally  first  coppered 
or  brassed. 

With  a  suitable  composition  of  the  nickel  bath  and  some 
experience,  the  last-mentioned  metals  may  also  be  directly 
nickeled  ;  but,  as  a  rule,  previous  coppering  or  brassing  is 
preferable,  the  certainty  and  beauty  of  the  result  being 
thereby  considerably  enhanced. 

Security  against  rust. — By  many  operators  it  is  preferred  to 
copper  iron  and  steel  articles  previous  to  nickeling,  it  being 
claimed  that  by  so  doing  better  protection  against  rust  is 
secured.  However,  comparative  experiments  have  shown 
that  with  the  thin  coat  of  copper  which,  as  a  rule,  is  applied, 
this  claim  is  scarcely  tenable,  and  the  conclusion  has  been 
reached  that  a  thick  deposit  of  nickel  obtained  from  a  bath  of 
suitable  composition  protects  the  iron  from  rust  just  as  well 
and  as  long  as  if  it  had  previously  been  slightly  coppered. 
It  cannot  be  denied  that  previous  coppering  of  iron  articles 
has  the  advantage  that  in  case  the  articles  have  not  been 
thoroughly  cleansed,  the  deposit  of  nickel  is  less  liable  to  peel 
off,  because  the  alkaline  copper  bath  completes  the  removal 
of  grease ;  but  with  objects  carefully  cleansed  according  to  the 


DEPOSITION    OF    NICKEL    AND    COBALT.  277 

directions  given  on  page  228,  previous  coppering  is  not  neces- 
sary. 

The  case,  however,  is  different  if  the  copper  deposit  is  pro- 
duced in  order  to  act  as  a  cementing  agent  for  two  nickel 
deposits.  If,  for  instance,  parts  which  have  previously  been 
nickeled,  and  from  which  the  old  deposit  cannot  be  removed 
by  mechanical  means,  are  to  be  re-nickeled,  coppering  is  re- 
quired, because  the  new  deposit  of  nickel  adheres  very  badly 
to  the  old.  Where  articles  are  to  be  protected  as  much  as 
possible  from  rust,  coppering  is  advisable,  but  the  best  success 
is  attained  by  a  method  different  from  the  one  generally  pur- 
sued. In  nickeling,  for  instance,  parts  of  bicycles  which  are 
exposed  to  all  kinds  of  atmospheric  influences,  they  are  first 
provided  with  a  thick  deposit  of  nickel,  then  with  a  thick  coat 
of  copper,  and  finally  again  nickeled,  they  thus  being  twice 
nickeled.  It  has  previously  been  mentioned  that  every  de- 
posit is  formed  net-like,  the  meshes  of  the  net  being  larger  or 
smaller,  according  to  the  nature  of  the  metal  deposited.  If 
now  thick  layers  of  two  different  metals  are  deposited  one  on 
the  top  of  the  other,  the  net-lines  of  one  deposit  do  not  con- 
verge into  those  of  the  previous  deposit,  but  are  deposited  be- 
tween them,  thus  consolidating  the  net.  It  will  now  be  readily 
understood  that  by  the  subsequent  polishing  the  further  con- 
solidation of  the  deposits  will  be  far  more  complete  than  when 
the  basis-metal  receives  but  one  deposit,  which  is  to  be  consoli- 
dated by  polishing.  It  is  a  remarkable  fact  that  the  porosity 
of  the  nickel  deposit  varies  if  the  article  is  nickeled  in  several 
baths  of  different  composition.  Thus  denser  deposits  may  be 
obtained  by  suspending  the  articles  in  two  or  three  baths, 
which  proves  that  the  different  resistances  of  the  respective 
baths  of  one  and  the  same  metal  exert  an  influence  upon  the 
greater  or  slighter  density  of  the  net. 

However,  under  certain  conditions,  even  iron  and  steel 
objects  doubly  nickeled  in  the  above-described  manner  do  not 
offer  a  sure  guarantee  against  rusting  of  the  basis-metal,  and 
to  absolutely  prevent  the  latter,  the  following  means  may  be 
adopted  : 


278  ELECTRO-DEPOSITION    OF    METALS. 

The  objects  are  provided  with  an  electro-deposit  of  zinc. 
This  deposit  is  scratch-brushed,  coppered  in  the  copper  cya- 
nide bath,  rinsed  in  water,  and  finally  nickeled,  at  first  with  a 
strong  current,  which  is  after  a  few  minutes  reduced  to  the 
normal  current-density.  It  is  recommended  to  polish  the 
•objects  thus  treated  with  circular  brushes,  and  not  use  polish- 
ing wheels  which  may  cause  them  to  become  heated,  because 
by  such  heating  blisters  are  readily  formed. 

Another  plan  is  as  follows :  The  objects  are  first  coppered 
in  the  copper  cyanide  bath.  The  thickness  of  this  deposit  is 
then  increased  to  0.15  or  0.2  millimeter  in  the  acid  copper 
bath  (see  Galvanoplasty).  It  is  then  polished  and  nickeled. 
Or,  if  there  is  sufficient  time,  a  very  thick  deposit  of  nickel  is 
directly  produced  upon  the  object  with  the  use  of  a  cold  ethyl 
sulphate  nickel  bath,  or  a  hot  quick  nickeling  bath  (see  pp. 
266  et  seq.). 

Tfie  objects  should  never  be  suspended  in  the  bath  without  cur- 
rent, since  the  baths,  with  few  exceptions,  exert  a  chemical 
action  upon  many  metals,  which  is  injurious  to  the  electro- 
plating process,  and  especially  with  nickel  baths  it  is  necessary 
to  connect  the  anode-rods  and  object-rods  before  suspending 
the  objects. 

Over-nickeling.  An  error  is  frequently  committed  in  nickel- 
ing with  too  strong  a  current,  the  consequence  being  that  the 
deposit  on  the  lower  portions  of  the  objects  soon  becomes  dull 
and  gray-black,  while  the  upper  portions  are  not  sufficiently 
nickeled.  This  phenomenon  is  due  to  the  reduction  of  nickel 
with  a  coarse  grain  in  consequence  of  too  powerful  a  current, 
and  is  called  burning  or  over-nickeling.  A  further  consequence 
of  nickeling  with  too  strong  a  current  is  that  the  deposit 
readily  peels  off  after  it  reaches  a  certain  thickness.  This 
phenomenon  is  due  to  the  hydrogen  being  condensed  and 
retained  by  the  deposit,  which  is  thereby  prevented  from 
acquiring  greater  thickness. 

Especially  do  those  objects  suspended  on  the  ends  of  the 
rods  nickel  with  great  ease.  This  evil  can  be  avoided  by 


DEPOSITION    OF    NICKEL    AND    COBALT.  279 

hanging  on  both  ends  of  the  rods  a  strip  of  copper-sheet  about 
0.39  inch  wide,  and  of  a  length  corresponding  to  the  depth  of 
the  bath. 

Normal  deposition.  The  following  criteria  may  serve  for 
judging  whether  the  nickeling  progresses  with  a  correct  cur- 
rent-strength: In  two,  or  at  the  utmost  three,  minutes,  all 
portions  of  the  objects  must  be  perceptibly  coated  with  nickel, 
but  without  a  violent  evolution  of  gas  on  the  objects.  Small 
gas  bubbles  rising  without  violence  and  with  a  certain  regu- 
larity are  an  indication  of  the  operation  progressing  with 
regularity.  If,  after  two  or  three  minutes,  the  objects  show  no 
deposit,  the  current  is  too  weak,  and  in  most  cases  the  objects 
will  have  acquired  dark,  discolored  tones.  In  such  case, 
either  a  stronger  current  must  be  introduced  by  means  of  the 
rheostat,  or,  if  the  entire  volume  of  current  generated  already 
passes  into  the  bath,  the  object-surface  has  to  be  decreased, 
or,  if  this  is  not  desired,  the  battery  must  be  strengthened  by 
adding  more  elements,  or  by  fresh  filling,  etc. 

If,  on  the  other  hand,  a  violent  evolution  of  gas  appears  on 
the  objects,  and  the  latter  are  well  covered  in  a  few  seconds, 
and  the  at  first  white  and  lustrous  nickeling  changes  in  a  few 
minutes  to  a  dull  gray,  the  current  is  too  strong,  and  must  be 
weakened  either  by  the  rheostat,  or  by  uncoupling  a  few 
elements,  or  diminishing  the  anode-surface,  or  finally  by 
suspending  more  objects  in  the  bath. 

These  criteria  also  apply  .to  nickeling  with  the  dynamo. 

The  most  suitable  current-density  for  nickeling  varies  very 
much,  as  will  be  seen  from  the  preceding  explanations.  For 
the  ordinary  cold  electrolysis  it  varies  for  copper,  brass,  iron, 
and  steel  from  0.3  to  1.5  amperes,  while  zinc,  previously  cop- 
pered, requires  1  to  1.2  amperes.  In  the  hot  nickel  bath  the 
current-density  may  be  up  to  5  and  more  amperes. 

In  nickeling  zinc  objects  greater  current-density  and  higher 
electro-motive  force  are  required.  If  the  current  is  not  of  suffi- 
cient strength,  black  streaks  and  stains  are  formed,  zinc  is  dis- 
solved, and  the  nickel  bath  spoiled.  These  evils  are  frequently 


280  ELECTRO-DEPOSITION    OF    METALS. 

complained  of  by  nickel-platers  who  have  not  a  clear  percep- 
tion of  the  prevailing  conditions  (see  polarization-current.)  A 
vigorous  evolution  of  gas  must  take  place  on  the  zinc  objects,, 
otherwise  a  serviceable  deposit  will  not  be  obtained. 

In  most  cases  the  electro-plater  will  in  a  few  days  learn  cor- 
rectly to  judge  the  proper  current-strength  by  the  phenomena 
presented  by  the  objects,  and  if  he  closely  follows  the  direc- 
tions given  but  few  failures  will  result.  It  may  here  be  again 
repeated  that  the  use  of  a  voltmeter  and  ammeter,  as  well  as 
of  a  rheostat,  greatly  facilitates  a  correct  estimate  of  the  proper 
current-strength,  and  these  instruments  should  for  the  sake  of 
economy  never  be  omitted  in  fitting  up  an  electro-plating 
plant. 

It  is  in  every  case  advisable  first  to  cover  the  objects,  i.  e., 
to  effect  the  first  deposit  of  nickel,  with  the  use  of  a  strong 
current,  in  order  to  withdraw  the  metals  from  the  action  of  the 
solution.  The  current  is  then  reduced  to  a  suitable  strength 
and  nickeling  finished  with  this  current.  With  a  current 
thus  regulated,  the  objects  may  be  allowed  to  remain  in  the 
bath  for  hours,  and  even  for  days.  It  is  further  possible  to. 
nickel  by  weight  and  attain  deposits  of  considerable  thickness. 

If  very  thick  deposits  of  nickel  are  to  be  produced  in  the 
ordinary  bath,  the  objects  must  be  frequently  turned,  as  the 
lower  portions  are  more  heavily  nickeled  than  the  upper;  fur- 
ther, as  soon  as  the  deposit  acquires  a  dull  bluish  luster,  it 
has  to  be  thoroughly  scratch-brushed,  in  doing  which,  how- 
ever, the  objects  must  not  be  allowed  to  become  dry.  After 
scratch-brushing  it  is  advisable  to  cleanse  the  deposit  once 
more  with  the  lime-brush,  and  after  rinsing  replace  the  objects 
in  the  bath.  If  burnt  places  cannot  be  brightened  and 
smoothed  with  the  scratch-brush,  the  desired  end  is  readily 
attained  with  the  assistance  of  emery  paper  or  pumice. 

For  solid  nickeling  it  suffices  for  most  articles,  with  a  nor- 
mal current  to  allow  them  to  remain  in  the  bath  until  a  mat 
bluish  shine  appears ;  this  is  ah  indication  that  the  deposit 
has  acquired  considerable  thickness,  provided  the  bath  has 


DEPOSITION    OF    NICKEL    AND    COBALT.  281 

not  been  alkaline.  In  alkaline  baths  this  dull  deposit  is  fre- 
quently formed  before  the  deposit  has  attained  considerable 
thickness  and  this  may  cause  errors,  if  the  reaction  of  the  bath 
is  not  frequently  controlled. 

If  the  mat  appearing  objects  are  permitted  to  remain  longer 
in  the  bath  without  scratch-brushing,  the  mat  bluish  tone 
soon  passes  into  a  mat  gray,  and  all  the  metal  deposited  in 
this  form  must  be  polished  away  in  order  to  obtain  a  bright 
luster. 

Whether  the  deposit  of  nickel  is  sufficiently  heavy  for  all 
ordinary  demands  is,  according  to  Fontaine,  shown  by  rub- 
bing a  nickeled  corner  or  edge  of  the  object  rapidly  and  with 
energetic  pressure  upon  a  piece  of  planed  soft  wood  until  it 
becomes  hot.  The  nickeling  should  bear  this  friction.  This 
test  can  be  recommended  as  perfectly  reliable. 

Faulty  arrangement  of  anodes.  If  the  objects,  after  having 
been  suspended  for  some  time  in  the  bath,  are  only  partially 
nickeled,  it  is  very  likely  due  to  the  defective  arrangement 
of  the  anodes.  This  occurs  chiefly  with  large  round  objects 
and  with  articles  having  deep  depressions  (cups,  vases,  etc.). 
It  is,  of  course,  supposed  that  the  wires  to  which  the  objects 
are  suspended  in  the  bath  have  a  sufficiently  large  cross- 
section  to  carry  the  current  required  for  nickeling  the  entire 
surface  of  the  object. 

For  flat  objects  suspending  them  between  two  rows  of  anodes 
suffices.  Round  objects  with  a  large  diameter  should  be  quite 
surrounded  with  anodes,  and  be  as  nearly  as  possible  equi- 
distant from  them.  This  arrangement  should  especially  not 
be  neglected  where  a  heavy  and  uniform  deposit  of  nickel  is 
to  be  applied  to  round  or  half-round  surfaces,  for  instance, 
large  half-round  stereotype  plates  for  revolving  presses. 

The  arrangement  of  two  object-rods  between  two  anode-rods 
is  permissible  only  for  small  and  thin  articles  such  as  safety- 
pins,  crochet  needles,  lead-pencil  holders,  etc.  For  articles 
with  larger  surfaces  it  is  decidedly  objectionable,  because  the 
sides  of  the  articles  turned  towards  the  anodes  acquire  a 


282  ELECTRO-DEPOSITION    OP    METALS. 

thicker  deposit  than  the  inside  surfaces,  and  the  thickness  of 
•the  deposit  decreases  with  the  distance  from  the  anodes. 

Nickeling  of  cavities  and  profiled  objects.  While  for  smooth 
articles  the.  most  suitable  distance  of  the  anodes  from  the 
objects  is  3|  to  5|  inches,  for  objects  with  depressions  and 
cavities  it  must  be  larger,  if  it  is  not  preferred  to  make  use 
of  the  methods  described  later  on.  However,  a  deposit  of  a 
uniform  thickness  cannot  be  obtained  by  this  means,  because 
the  portions  nearer  to  the  anodes  will  acquire  a  thicker  de- 
posit than  the  cavities  ;  hence  the  use  of  a  small  hand  anode, 
which  is  connected  by  means  of  a  thin,  flexible  wire  with  the 
anode-rod,  and  introduced  into  the  depressions  and  cavities,  is 
to  be  preferred.  This,  of  course,  renders  it  necessary  for  a 
workman  to  stand  alongside  the  bath  and  execute  the  opera- 
tion by  hand  ;  but  as  the  small  anode  can  be  brought  within 
a  few  millimeters  of  the  surface  of  the  article,  and  at  this  dis- 
tance slowly  moved  around  it,  a  correspondingly  thick  deposit 
is  in  a  short  time  formed. 

At  any  rate  baths  in  which  objects  with  depressions  and 
profiled  articles  are  to  be  nickeled  must  possess  greater  resist- 
ance than  baths  for  nickeling  flat  articles,  and  it  is  inexplica- 
ble why  a  bath  with  a  large  content  of  ammonium  chloride 
and  consequently  slight  conducting  resistance  can  be  recom- 
mended, as  has  been  done,  for  nickeling  hollow  articles. 
When  baths  containing  ammonium  chloride  are  used  for  nick- 
eling articles  with  deep  cavities  the  portions  nearest  to  the 
anodes  will  frequently  be  found  overnickeled — burnt — before 
the  deepest  portions  are  at  all  covered  with  nickel,  and  if  the 
operator  waits  until  the  deposit  upon  the  latter  portions  has 
-acquired  the  desired  thickness,  the  deposit  already  peels  off 
from  the  former  portions,  and  frequently  before  that  time.  By 
•comparative  experiments  in  nickeling  the  inside  of  brass  tubes, 
15  millimeters  in  diameter,  it  was  found  that  in  a  bath  with  great 
resistance,  as  well  as  in  one  with  slight  resistance,  nickeling 
was  equally  well  effected.  However,  the  phenomenon  of  peel- 
ing off,  above  referred  to,  appeared  in  the  bath  which  contained 


DEPOSITION    OF    NICKEL    AND    COBALT.  283 

ammonium  chloride  when  the  ends  of  the  120-millimeter  long 
tubes  turned  away  from  the  anode  were  still  so  slightly  nick- 
eled that  the  basis-metal  showed  through.  On  the  other 
hand /in  the  bath  without  ammonium  chloride  the  end  of  the 
tube  turned  towards  the  anode,  to  be  sure,  became  mat,  but 
did  not  peel  off  in  polishing,  and  nickeling  in  the  interior  of 
the  tube  had  progressed  well  to  the  opposite  end,  the  basis- 
metal  there  being  well  covered. 

In  nickeling  lamp-feet  of  cast-zinc,  the  use  of  the  hand- 
anode  can  scarcely  be  avoided  if  the  depressed  portions  also 
are  to  be  provided  with  a  uniformly  good  deposit.  Moreover, 
zinc  articles  form  an  exception  to  the  general  rule  in  so  far  as 
by  reason  of  the  highly  positive  properties  of  zinc,  the  resist- 
ance of  the  bath  may  be  slighter  than  the  baths  for  nickeling 
copper  and  its  alloys,  as  well  as  iron  and  steel. 

Besides  the  above-mentioned  general  rules  for  nickeling, 
which  also  hold  good  for  other  electro-plating  purposes,  the 
following  may  be  given  : 

In  suspending  the  objects  in  the  bath,  rub  the  metallic 
hooks  or  wires,  with  which  they  are  secured  to  the  rods,  a  few 
times  to  and  fro  upon  the  rod,  in  order  to  be  sure  that  the 
place  of  contact  is  purely  metallic.  It  is  also  well  to  acquire 
the  habit  of  striking  the  rod  a  gentle  blow  with  the  finger 
every  time  when  suspending  an  object,  the  gas-bubbles  settling 
on  the  articles  becoming  thereby  detached  and  rising  to  the 
surface.  It  is  further  advisable,  before  securing  the  objects  to 
the  object-rod,  to  move  them  up  and  down  several  times ;  so 
to  say,  shake  them  beneath  the  fluid,  whereby,  on  the  one 
hand,  the  layers  poorer  in  metal  are  mixed  with  those  richer 
in  metal,  and,  on  the  other,  any  dust  which  may  float  upon 
the  bath  and  settle  on  the  objects  is  removed. 

The  objects  suspended  in  the  bath  should  not  touch  one 
another,  nor  one  surface  cover  another,  and  thus  withdraw  it 
from  the  direct  action  of  the  anode.  In  the  first  case  stains 
will  readily  form  on  the  places  of  contact,  and,  in  the  latter, 
the  covered  surface  acquires  only  a  slight  deposit.  That  the 
objects  must  not  touch  the  anodes  need  scarcely  be  mentioned. 


284  ELECTRO  DEPOSITION    OF    METALS. 

Objects  with  depressions  and  cavities  should  be  suspended 
in  the  bath  so  that  the  air  in  the  depressions  and  cavities  can 
escape,  which  is  effected  by  turning  the  depression  upwards, 
or,  if  there  are  several  depressions  on  opposite  sides,  bf  turn- 
ing the  articles  about  after  being  introduced  into  the  bath. 
Air-bubbles  remaining  in  the  hollows  prevent  contact  with 
the  solution,  no  deposit  being  formed  on  such  places. 

Polarization.  It  remains  to  say  a  few  words  in  regard  to  the 
so-called  polarization  phenomena.  In  the  theoretical  part  of 
this  work,  it  has  been  shown  that  by  dipping  two  plates  of 
different  metals  in  a  fluid  a  counter  or  polarization  current  is 
generated,  which  is  the  stronger  the  greater  the  difference  in 
the  potentials  of  the  two  metals  in  the  solution  is.  If  the 
anodes  in  a  nickel  bath  consist  of  nickel  and  the  objects  of 
copper,  the  counter-current  will  be  slight.  It  becomes,  how- 
ever, greater  when  iron  objects  are  suspended  in  the  bath,  and 
still  greater  with  zinc  surfaces  which  are  to  be  nickeled,  be- 
cause with  the  solutions  here  in  question,  zinc  possesses  towards 
nickel  an  essentially  higher  potential.  Now,  since  the  counter- 
current  flows  in  a  direction  opposite  to  that  of  the  current 
introduced  at  the  bath,  the  latter  is  weakened,  and  the  more 
so  the  stronger  the  counter-current  is.  This  explains  why 
iron  requires  a  stronger  current  for  nickeling  than  copper- 
alloys,  and  zinc  a  stronger  one  than  iron. 

Now  it  may  happen  that  the  counter-current  becomes  so 
strong  as  to  entirely  check  the  effect  of  the  main  current,  and 
even  to  reverse  the  latter,  the  consequence  being  that,  in  the 
first  case,  the  formation  of  the  deposit  is  interrupted,  and,  in 
the  latter,  that  the  deposit  is  again  destroyed,  arid  the  metals 
of  which  the  articles  consist  dissolve  and  contaminate  and 
spoil  the  bath.  To  avoid  this,  a  main  current  must  be  con- 
ducted into  the  bath,  which,  by  its  sufficiently,  large  electro- 
motive force  can  overcome  the  counter-current,  and  the  con- 
sequences of  the  reversal  of  the  current  can  be  prevented  by 
using  the  galvanometer  and  observing  the  deflection  of  its 
needle,  which  (according  to  p.  143)  in  proper  time  indicates 


DEPOSITION    OF    NICKEL    AND    COBALT.  285 

the  appearance  of  a  reversed  current.  Now  if  a  nickel-plater 
has  only  a  slight  current  at  his  disposal,  it  follows  from  the 
above  explanation  that,  before  nickeling  the  more  electro- 
positive metals,  such  as  iron,  tin,  zinc,  it  is  best  first  to  copper 
them,  and  thereby  overcome  the  action  of  these  metallic 
surfaces  as  regards  the  formation  of  the  counter-current. 

It  happens  comparatively  seldom  that  the  counter-current 
becomes  so  strong  as  to  destroy  the  deposits  formed,  because 
for  nickeling  powerful  Bunsen  cells  with  two  acids,  or  a 
•dynamo  with  at  least  4  volts'  impressed  electro-motive  force, 
are  generally  used.  It  is,  however,  well  to  acquaint  the  oper- 
ator with  all  possible  contingencies,  and  to  explain  the  reason 
why  the  articles  are  preferably  covered  with  a  strong  current. 
Sprague  recommends  an  initial  current  of  5  volts'  electro- 
motive force,  but  in  most  cases  one  of  3.5  volts  suffices  for 
nickeling  iron  and  copper  alloys. 

Stripping  defective  nickel.  Defective  nickeling  must,  as  a 
rule,  be  completely  removed  before  the  objects  can  be  nick- 
eled, since  the  second  deposit  does  not  adhere  to  the  previous 
•one,  but  frequently  peels  off  in  polishing  or  by  slightly  bend- 
ing the  object.  The  reasons  for  this  behavior  are  :  1.  Like 
iron,  nickel  readily  oxidizes  on  the  surface,  but  this  oxidation 
is  not  so  heavy  as  to  be  perceptible.  Previous  to  nickeling 
this  oxide  has  not  been  completely  removed  and  in  the  case 
of  quite  old  plated  objects  the  nickel  has  had  a  chance  to 
oxidize.  Nickel,  however,  adheres  firmly  only  to  metallic 
nickel  and  not  to  the  oxide ;  hence  the  second  deposit  peels 
off.  2.  In  case  the  deposit  is  comparatively  new  and  has  not 
been  exposed  for  some  time  to  the  action  of  atmospheric  air, 
the  peeling  off  of  nickel  deposited  upon  nickel  is,  as  a  rule, 
caused  by  the  polishing  material  remaining  upon  the  surface. 
Vienna  lime  and  similar  agents  which  contain  paraffin  and 
•other  mineral  fats  and  wax  are  much  used  for  polishing 
nickel.  These  substances  partially  penetrate  into  the  pores  of 
the  deposited  nickel  or  remain  upon  the  surface.'  By  the 
ordinary  means  of  cleaning  the  mineral  fats  or  wax  are  not 


286  ELECTRO-DEPOSITION    OF    METALS. 

removed,  the  consequence  being  that  the  second  deposit  of 
nickel  does  not  adhere.  With  the  use  of  animal  fats,  which 
readily  saponify,  as  polishing  agents,  the  case  is  not  so  bad, 
but  even  under  these  conditions,  the  nickel  has  a  tendency  to 
peel  off.  It  must  be  borne  in  mind  that  as  previously  men- 
tioned, all  electrolytically  produced  deposits  are  composed  of  a 
net-work  of  very  minute  crystals,  the  deposit  being  thus  of  a 
porous  nature.  In  polishing  larger  or  smaller  quantities  of 
the  polishing  agent  penetrate  into  these  pores,  and  their  com- 
plete removal  is  a  very  difficult  matter. 

For  the  removal  of  the  nickel  coating  the  following  strip- 
ping acid,  which  may  be  used  either  cold  or  tepid,  has  been 
recommended  :  Sulphuric  acid  of  66°  Be.,  4  Ibs.  ;  nitric  acid 
of  40°  Be.,  1  Ib.  ;  water  about  1  pint.  First  put  the  water  in 
a  stoneware  jar  and  cautiously  add,  a  little  at  a  time,  the  sul- 
phuric acid,  since  considerable  heat  is  generated  when  this 
acid  is  mixed  with  water.  When  the  entire  quantity  of  sul- 
phuric acid  has  been  added,  pour  in  the  nitric  acid,  when  the- 
bath  is  ready  for  use.  In  making  up  the  stripping  bath,  the 
proportions  of  the  acids  may  be  varied,  but  the  foregoing  will 
be  found  to  answer  every  purpose.  An  addition  of  8  ozs.  of 
potassium  nitrate  to  the  bath  has  also  been  recommended. 

When  stripping  nickel-plated  articles  in  the  above  bath  it  is 
necessary  to  watch  the  operation  attentively,  since  some  arti- 
cles are  very  lightly  coated  and  a  momentary  dip  is  frequently 
sufficient  to  deprive  them  of  their  nickel.  Other  articles  which 
have  been  thoroughly  well  nickeled,  but  require  from  some 
accidental  cause  to  be  stripped  and  re-nickeled,  will  need  im- 
mersion for  several  minutes ;  indeed  well  nickeled  articles  may 
occupy  nearly  half  an  hour  in  stripping  before  the  underlying 
surface  is  entirely  bare.  The  operation  of  stripping  should  be 
conducted  in  the  open  air,  or  in  a  fire-place,  so  that  the  acid 
fumes,  which  are  very  pernicious,  can  escape  freely.  The 
articles  should  be  attached  to  a  stout  copper  wire,  and  after  a 
few  moments'  immersion  should  be  removed  from  the  bath  to 
see  how  the  operation  progresses,  it  being  absolutely  necessary 


DEPOSITION    OF'  NICKEL    AND    COBALT.  287 

that  the  work  should  not  remain  in  the  stripping  solution  one 
instant  after  the  nickel  is  removed.  The  object  is  then  trans- 
ferred to  a  large  volume  of  cold  water,  and  after  washing  twice 
or  three  times  in  fresh  water  is  ready  for  the  subsequent  stages 
of  the  process.  When  stripping  has  been  properly  effected, 
the  underlying  metal  exhibits  a  bright,  smooth  surface,  giving 
little  evidence  of  the  mixture  having  acted  upon  it. 

Many  platers,  however,  prefer  to  remove  the  nickel  coating 
mechanically  by  brushing  with  emery.  From  depressions  it 
is  as  much  as  possible  removed  with  the  brush,  after  which  the 
object  is  freed  from  grease  and  pickled,  and  coppered  before 
nickeling.  In  this  case  the  layer  of  copper  serves  for  cement- 
ing together  the  old  and  new  deposits,  and  there  will  be  no 
danger  of  the  new  deposit  peeling  off  in  polishing. 

It  has  also  been  proposed  to  strip  by  electrolysis  by  making 
the  object  the  anode  in  an  old  nickel  bath,  Attention  is 
equally  necessary  in  conducting  this  process  to  guard  against 
any  attack  upon  the  basis-metal ;  but  since  it  is  impossible  to 
prevent  all  action,  no  bath  which  is  to  be  afterward  employed 
for  depositing  the  metal  should  be  used  for  this  purpose,  as  it 
will  become  gradually  charged  with  impurities.  A  10  per 
cent,  solution  of  sulphuric  acid  in  water  may  be  equally 
readily  adapted  to  the  electrolytic  stripping. 

Many  nickel-plated  iron  and  steel  objects  are  so  cheap  that 
it  does  not  pay  to  strip  the  nickel  from  them,  and  it  is  best  to 
throw  them  on  the  scrap  pile.  In  some  cases,  however,  for 
instance,  surgical  instruments,  fire-arms,  fine  cutlery  and 
other  more  expensive  articles,  it  is  frequently  desirable  to  re- 
move the  old  nickel  deposit.  To  be  sure,  nitric  acid  would 
remove  the  nickel,  but  it  also  attacks  iron  and  steel  and 
causes  pitting.  For  stripping  such  articles  by  electrolysis  the 
following  bath  has  been  recommended  :  Water  1  lb.,  potas- 
sium cyanide  1.8  ozs.,  yellow  prussiate  of  potash  0.5  oz.  The 
iron  or  steel  object  to  be  stripped  is  suspended  as  anode  in  the 
bath,  which  should  be  used  at  a  temperature  of  122°  F.  A 
sheet  of  iron  or  steel  serves  as  cathode.  For  stripping  a  thin 


288  ELECTRO-DEPOSITION    OF    METALS. 

deposit  only  a  few  hours  are  required,  but  a  whole  day  for 
thick  deposits.  However,  the  operation  requires  no  special 
attention,  as  the  iron  or  steel  surface  is  not  attacked  and  there 
is  no  danger  of  pitting.  The  current-strength  should  be  the 
same  as  usually  employed  for  nickel-plating. 

As  a  remedy  against  the  yellowish  tone  of  the  nickeling, 
Pfanhauser  recommends  suspending  the  nickeled  articles,  im- 
mediately after  taking  them  from  the  nickel  bath,  as  anodes 
in  a  nickel  bath  acidulated  with  citric  or  hydrochloric  acid,  a 
piece  of  sheet  nickel  serving  as  the  cathode,  and  to  allow  the 
current  to  act  for  a  few  seconds.  It  is  claimed  that  thereby 
the  basic  nickel  salts  separated  together  with  the  nickel,  and 
to  which,  according  to  Pfanhauser,  the  yellowish  tinge  is  due, 
are  dissolved,  and  the  nickeling  will  show  a  pure  white  tone. 

As  nickel  anodes  contain,  as  a  rule,  iron,  a  minute  quantity 
of  this  metal  is  deposited  together  with  the  nickel,  and  the 
latter  is  inclined  to  form  a  mat  surface  or  to  tarnish.  If  the 
objects  are  to  be  polished  this  does  not  matter,  but  if  they  are 
not  to  be  polished  slight  mat  stains  frequently  appear  upon 
the  surface  after  drying.  Such  stains  can  be  removed  by  the 
use  of  a  bath  of  dilute  hydrochloric  acid  (2  parts  water,  1  part 
acid).  After  thoroughly  rinsing  the  object  in  water,  immerse 
it  for  a  moment  in  the  acid  bath,  and  then  rinse  again  care- 
fully. Now,  without  drying,  draw  the  object  through  a  soap- 
bath  and  rinse  again.  Since  the  soap  solution  leaves  a  thin 
film  of  oil  upon  the  nickel  surface  not  much  water  will  adhere 
to  it,  and  it  will  quickly  dry.  It  will  be  found  that  the  mat 
spots  have  disappeared  or  the  stains  are  scarcely  perceptible. 

Defective  nickeling.  The  following  is  a  brief  resume  of  the 
principal  defects  which  may  occur  in  nickeling,  as  well  as  the 
means  of  avoiding  them  : 

1.  The  articles  do  not  become  coated  with  nickel,  but 
acquire  discolored,  generally  darker,  tones.  Reason:  The 
current  is  either  too  feeble  to  effect  the  reduction  of  nickel, 
and  the  coloration  is  due  to  the  chemical  action  of  the  nickel 
solution  upon  the  metals  constituting  the  objects.  This  phe- 


DEPOSITION    OF    NICKEL    AND    COBALT.  289 

noraenon  is  frequently  observed  in  nickeling  zinc  articles. 
Remedy :  Increase  the  current  or  diminish  the  area  of  sus- 
pended objects ;  also  examine  whether  the  current  actually 
passes  into  the  bath,  otherwise  clean  the  places  of  contact. 

2.  A  deposition  of  nickel  takes  place,  but  it  is  dark  or 
spotted  or  marbled,  even  with  a  sufficiently  strong  current. 
Reasons :  The  bath  is  either  alkaline,  which  has  to  be  ascer- 
tained by  testing  with  litmus-paper,  and,  if  so,  the  slightly 
acid  reaction  of  the  bath  has  to  be  restored  by  the  addition  of 
a,  suitable  acid ;  or,  the  bath  is  too  concentrated,  in  which 
•case  a  separation  of  crystals  will  be  observed — this  is  remedied 
by  diluting  with  water  ;  or,  the  nickel  solution  is  very  poor  in 
metal,  which  can  be  remedied  by  the  addition  of  nickel  salt ; 
it  should  also  be  tested  as  to  the  admixture  of  copper,  the 
production  of  dark  tones  being  frequently  due  to  this — in  this 
case  the  bath  is  allowed  to  work  for  some  time,  and  if  the 
content  of  copper  is  inconsiderable  a  white  deposit  will  soon 
be  obtained  ;  or,  the  cleaning  and  pickling  of  the  articles  have 
not  been  thoroughly  done,  which  is  remedied  by  again  clean- 
ing them  ;  or,  the  conducting  power  of  the  bath  is  insufficient, 
which  is  remedied  by  the  addition  of  a  suitable  conducting 
salt. 

When  freshly  prepared  baths  yield  dark  nickeling,  it  can 
generally  be  remedied  by  working  the  bath  two  or  three 
hours,  if  it  is  not  over-concentrated  and  the  cause,  as  above 
mentioned,  has  to  be  looked  for  in  a  small  content  of  copper 
in  the  nickel  salt. 

3.  A  yellowish  tinge  of  the  nickeling.     Reason :  Alkalinity 
of  the  bath.     Remedy :  See  under  2  ;  or,   with  cast-iron,  an 
insufficient  metallic  surface,  which  is  remedied  by  repeating 
the  scratch-brushing ;  or,  unsuitable  composition  of  the  bath. 

4.  The  objects  rapidly  acquire  a  white  deposit  of  nickel, 
but  the  color  soon  changes  to  a  dull  gray-black,  especially  on 
the  lower  edges  and  corners.     Reason :  Too  strong  a  current. 
Remedies :  Regulating  the  current,  or  suspending  more  objects, 
or  uncoupling  elements.     Frequent  turning  of  the  articles. 

19 


290  ELECTRO-DEPOSITION    OF    METALS, 

5.  The  nickeling  is  white,  but  readily  peels  off  by  scratching 
with  the  finger-nail,  or  by  the  action  of  the  polishing  wheel. 
Reasons:  The  current  is  too  strong,  which  is  remedied  as  under 
4 ;  or,  the  bath  is  too  acid — this  is  remedied  by  the  addition  of 
ammonia,  potassium  carbonate,  or  nickel  carbonate,  according 
to  the  composition  of  the  bath;  or,  freshly  prepared  nickel  bath 
or  freshly  made  additions,  this  being  remedied  by  working  the 
bath  and  by  very  careful  regulation  of  the  current  in  nickeling 
during  the  first  days ;  or,  insufficient  cleaning  and  pickling, 
which  is  remedied  by  thorough  cleaning  after  removing  the  de- 
fective deposit,  or,  if  it  cannot  be  entirely  removed,  coppering. 

6.  Though  nickeling  may  proceed  in  a  regular  manner, 
some  places  remain  free  from  deposit.     Reasons:  Either  the 
surfaces  of  some  of  the  objects  touch  one  another ;   or,  are 
stained  by  having  been  touched  with  dirty  fingers ;  or,  air 
bubbles  are  inclosed  in  cavities.     Remedy:  Removal  of  the- 
causes. 

7.  The  deposit  appears  with  small  holes.     Reason :  A  de- 
posit of  particles  of  dust  upon  the  objects.     Remedy :  Remove- 
the  dust  from  the  surface.     When  there  is  a  general  turbidity 
of  the  bath  in  consequence  of  alkalinity,  add  the  most  suitable 
acid,  and  boil  and  filter  the  bath;  or,  insufficient  removal  of  gas 
bubbles  from  the  objects.     Remedy :  Shake  the  object-rods  by 
blows  with  the  finger. 

8.  Deposition  takes  place  promptly  upon  the  portions  of 
the  objects  next  to  the  anodes,  while  deeper  portions  remain 
free  from    nickel   or   become  black.     Reason :   Too  slight  a 
distance  of  the  objects  from  the  anodes.     Remedy  :  Increasing 
the  distance  ;  with  large  depressions,  treatment  with  the  hand- 
anode. 

Refreshing  nickel  baths. — According  to  their  composition,, 
the  amount  of  work  performed,  and  the  anodes  used,  the  baths 
will  in  a  shorter  or  longer  time  require  certain  additions  in 
order  to  keep  their  action  constant.  By  "  refreshing  "  is  not 
understood  the  small  addition  of  acid  or  alkali  from  time  to 
time  required  for  restoring  the  original  reaction  of  the  baths,. 


DEPOSITION    OF    NICKEL    AND    COBALT.  291 

but  additions  intended  to  increase  the  metallic  content  and 
the  diminished  conductivity. 

The  metallic  content  is  increased  by  boiling  the  bath  with 
some  of  the  nickel  salt  used  in  its  preparation,  while  the  con- 
ductivity is  improved  by  adding,  at  the  same  time,  so  much 
conducting  salt  as  is  necessary  to  restore  the  electro-motive 
force  originally  required.  Nothing  definite  can,  of  course,  be 
said  in  regard  to  the  quantity  of  such  additions,  it  being  ad- 
visable to  observe  their  effect  on  a  small  portion  of  the  bath, 
so  as  to  be  sure  not  to  spoil  the  entire  bath. 

Nickel  baths  bear,  as  a  rule,  refreshing  several  times,  but 
as  in  the  course  of  time  they  take  up  impurities,  even  when 
the  greatest  care  is  exercised,  it  is  best  to  refresh  them  at  the 
utmost  twice,  and  then  to  renew  them  entirely. 

The  treatment  of  the  articles  after  nickeling,  as  well  as  after 
all  electro-plating  processes,  has  already  been  described,  and 
it  is  only  necessary  here  to  refer  again  to  the  fact,  that  with 
articles  of  iron  and  steel,  immersion  in  boiling  water  before 
drying  in  sawdust  is  absolutely  necessary,  and  subsequent 
drying  in  a  drying  chamber  is  also  a  great  safeguard  a& 
regards  stability  and  protection  against  rust. 

Nickel  deposits  are  polished  upon  felt  wheels  or  bobs  of  cloth, 
muslin  or  flannel,  with  the  use  of  Vienna  lime,  rouge,  Victor 
white  polish,  etc.  (See  "  Polishing,"  p.  216).  To  give  the 
objects  the  highest  luster  possible,  it  is  advisable  finally  to 
polish  them  upon  a  woolen  brush  with  dry  Vienna  lime. 

Sharp  edges,  corners  and  raised  portions  should  be  held 
only  with  slight  pressure  against  the  polishing  wheels,  they 
being  more  strongly  attacked  by  them  than  flat  surfaces.  The 
latter  can  stand  a  stronger  pressure  without  fear  of  cutting 
through  the  deposit,  provided  the  latter  is  of  sufficient  thick- 
ness and  hardness. 

Knife  blades  and  surgical  instruments  with  sharp  edges 
require  special  care  in  polishing,  which  will  later  on  be  re- 
ferred to. 

Cleansing  polished  objects.      After   polishing,   the  nickeled 


292  ELECTRO-DEPOSITION    OF    METALS. 

objects,  especially  those  with  depressions,  have  to  be  freed 
from  polishing  dirt  by  brushing  with  hot  soap-water,  or  dilute 
ihot  caustic  lye,  or  benzine,  then  rinsed  in  hot  water  and  dried. 

Calculation  of  the  nickeling  operation.  Many  inquiries  re- 
garding the  mode  of  calculating  the  price  to  be  charged  for 
nickeling  objects  give  rise  to  the  following  remarks :  If  the 
same  article  with  the  same  definite  surface  is  always  to  be 
nickeled,  the  calculation  is  quite  simple.  From  the  current- 
strength  and  the  time  required  for  nickeling,  the  weight  of 
the  nickel-deposit  can  be  readily  determined  by  keeping  in  view 
that  1  ampere  theoretically  deposits  in  1  hour  1.1  gramme 
of  nickel,  or  about  1  gramme  if  the  current  output  be  taken 
into  consideration.  The  value  of  the  ascertained  weight  has 
to  be  determined  by  taking  the  cost  of  the  anodes  as  the  basis, 
and  from  this  is  calculated  the  constant  price  of  the  separate 
piece.  To  this  has  to  be  added  the  wages  for  grinding,  pol- 
ishing and  nickeling,  as  well  as  the  amount  of  power  required, 
which,  according  to  the  motors  in  use,  has  to  be  established 
by  a  special  calculation  ;  further,  the  materials  used  for  grind- 
ing, polishing,  freeing  from  grease,  etc.,  and  a  certain  profit. 
However,  in  most  cases  it  is  scarcely  possible  to  make  such 
detailed  calculations  in  electro-plating  establishments  in  which 
the  most  diverse  objects  have  to  be  nickeled,  because,  on  the 
one  hand,  the  determination  of  the  surface  of  the  separate 
objects  would  be  difficult  and  time-consuming,  and  on  the 
other,  it  would  be  very  troublesome,  in  consequence  of  the 
-change  of  the  object-surfaces  in  the  bath,  to  keep  an  accurate 
account  of  the  current-strength  and  time  required  for  the 
.separate  objects. 

To  attain  the  object,  it  has  in  practice  proved  the  simplest 
.plan  to  take  as  a  basis  the  wages  paid  to  the  grinder  and 
ipolisher,  and  multiply  them  by  4,  in  order  to  obtain  the  sell- 
ring  price  of  the  work  furnished.  The  selling  value  thus  deter- 
mined includes  all  expenses  and  a  fair  profit.  Somewhat  more 
•will  have  to  be  allowed  for  particularly  complicated  objects 
which  .require  assistance  with  the  hand-anode.  This  mode  of 


DEPOSITION    OP    NICKEL    AND    COBALT.  293 

calculation  has  on  the  whole  been  found  to  answer  for  solid, 
heavy  nickeling.  .For  light  nickeling — coloring  white  in  the 
nickel  bath — the  selling  value  might  be  too  high.  An  extra 
charge  will  of  course  have  to  be  made  for  repairing  articles 
which  are  received  for  nickeling. 

When  objects  already  ground  and  polished  are  sent  in  to  be 
nickeled,  the  above-mentioned  mode  of  calculation  is  of  course 
not  applicable.  In  that  case  it  has  to  be  calculated  how  much 
a  charge  of  a  bath  must  bring,  in  order  to  cover  expenses  and 
a  certain  profit,  and  from  that  the  approximate  selling  value 
of  the  nickeling  work  may  be  determined. 

Nickeling  small  and  cheap  objects  in  large  quantities.     This  is 

FIG.  114. 


effected  by  stringing  the  objects,  if  feasible,  upon  a  copper  wirer 
and  placing  a  large  glass  bead  between  every  two  objects,  to- 
prevent  the  surfaces  from  sticking  together  in  the  bath.  Such 
objects  being  generally  only  slightly  nickeled,  it  suffices  to- 
allow  them  to  remain  for  a  few  minutes  only  in  the  bath  with 
a  strong  current,  it  being  advisable  to  diligently  shake  the 
bundles  in  order  to  effect  a  change  of  position  of  the  objects 


294  ELECTRO-DEPOSITION    OF    METALS. 

and  prevent  their  touching  one  another,  notwithstanding  the 
glass  bead  placed  between  them. 

Very  small  objects,  such  as  rivets,  pins,  etc.,  which  cannot  be 
strung  upon  wire,  are  nickeled  in  dipping  baskets  of  stoneware 
or  wire.  To  the  bottom  of  the  dipping  basket  is  secured  a 
copper  or  brass  wire,  which  is  connected  with  the  object-rod, 
and  the  articles,  not  too  many  at  a  time,  are  then  placed  in 
the  basket.  During  the  operation  the  articles  must  be  con- 
stantly shaken,  and  as  nickel  baths,  as  a  rule,  do  not  conduct 
sufficiently  well  to  properly  nickel  the  objects  in  the  basket, 
it  is  advisable  to  hold  with  one  hand  an  anode,  connected  by 
a  flexible  wire  with  the  anode- rod,  in  the  basket,  while  the 
other  hand  holds  the  basket  (Fig.  114)  and  constantly  shakes 

FIG.  115. 


and  turns  it.     For  nickeling  in  the  dipping  basket  it  is  further 
advisable  to  heat  the  nickel  bath. 

In  place  of  a  stoneware  dipping  basket,  a  basket  tray  of 
brass  wire,  Fig.  115,  to  which  are  soldered  two  copper  wires 
for  suspending  it  to  the  object-rod,  may  preferably  be  used. 
From  the  soldered  places  a  few  copper  wires  extend  to  the 
bottom  of  the  basket.  To  prevent  the  basket  from  becoming 
covered  with  nickel  it  is  coated  with  asphalt  varnish.  At  a 
distance  of  about  2J  to  3  inches  below  the  basket  an  anode  is 
arranged  in  horizontal  position,  while  with  one  hand  a  hand- 
anode  is  held  over  the  small  articles  in  the  basket.  By  this 
arrangement  a  thicker  deposit  is  more  rapidly  obtained, 
especially  if,  with  the  other  hand,  the  articles  are  constantly 
stirred  by  means  of  a  glass  or  wooden  rod. 


DEPOSITION    OF    NICKEL    AND    COBALT.  295 

Warren  has  described  a  solution  of  nickel  and  one  of  cobalt 
which  can  be  decomposed  in  a  simple  cell  apparatus.  With 
the  nickel  solution,  which  was  prepared  by  dissolving  100 
parts  by  weight  of  nickel  chloride  in  as  little  water  as  possible 
and  mixing  with  a  concentrated  solution  of  500  parts  of 
Rochelle  salts,  no  satisfactory  results  could  be  obtained.  The 
•cobalt  solution  however  yielded  good  results,  and  would  seem 
to  be  suitable  for  electro-plating  small  objects  in  large  quan- 
tities. It  will  be  further  referred  to  under  "  Deposition  of 
Cobalt." 

In  the  last  few  years  a  number  of  contrivances  for  electro- 
plating small  articles  in  large  quantities  have  been  patented, 
the  articles  to  be  plated  being,  as  a  rule,  contained  in  a  revolv- 
ing perforated  drum.  The  drums  of  some  of  the  contrivances 
are  constructed  of  non-conducting  material  so  that  the  articles 
receive  the  current  through  copper  or  other  metallic  strips, 
which  are  secured  in  the  inside  walls  of  the  drums,  and  are 
brought  in  various  ways  in  contact  with  the  source  of  current. 
In  other  contrivances,  for  instance,  the  apparatus  of  Smith  & 
Deakin,  metallic  pins  capable  of  being  turned  around  the 
shaft,  which  is  in  contact  with  the  negative  pole  of  the  source 
of  current,  reach  to  the  layer  of  articles  in  the  drum,  and 
effect  the  re-transmission  of  the  current.  Since  in  the  con- 
trivances mentioned  the  anodes  are  placed  outside  of  the 
drum,  and  the  latter  acts  as  a  diaphragm  with  great  resist- 
ance, a  very  high  electro-motive  force  is  required  for  the  pro- 
duction of  the  deposit,  independent  of  the  fact  that  the  articles 
being  in  constant  motion  already  require  an  essentially  higher 
electro-motive  force. 

In  another  class  of  apparatus,  the  six  or  eight-cornered  drum 
is  constructed  of  the  same  metal  which  is  to  be  deposited. 
Every  metal  plate  forming  one  side  is  insulated  from  the  next 
plate.  The  plates  which,  while  the  drum  is  revolving,  occupy 
the  lowest  position  and  upon  which  the  articles  for  the  time 
being  rest,  are  brought  into  contact  with  the  negative  pole  of 
the  source  of  current  by  a  commutator  of  special  construction, 


296 


ELECTRO-DEPOSITION    OF    METALS. 


while  the  positive  current  is  carried  to  the  plates  occupying  a 
higher  position,  they  thus  acting  as  anodes.  In  this  type  of 
apparatus  the  high  resistance  due  to  the  arrangement  of  the 
anodes  on  the  outside  is  overcome,  but  the  commutator  with 
the  sliding  contact  constitutes  a  very  sensitive  part  of  the 
construction. 

Fig.  116  shows  a  mechanical  electro-plating  apparatus 
patented  and  manufactured  by  The  Hanson  and  Van  Winkle 
Co.,  Newark,  N.  J.  The  apparatus  complete  consists  of  an 

FIG.  116. 


outer  wooden  tank  for  containing  the  solution,  a  perforated 
revolving  plating  barrel,  made  of  wood  or  celluloid  in  which 
to  hold  and  tumble  the  work  while  deposition  is  going  on,. 
and  necessary  rods  and  connections.  The  size  of  the  perfora- 
tions required  in  the  plating  barrel  depends  on  the  class  and 
shape  of  the  work  to  be  plated.  The  perforations  should  be 
as  large  as  possible  without  allowing  the  work  to  slip  through 
or  catch  in  them.  The  barrel  is  entirely  submerged,  thus 
permitting  a  much  larger  quantity  of  work  in  each  batch. 


DEPOSITION    OF    NICKEL    AND    COBALT.  297 

The  drive  is  from  the  outside,  thus  avoiding  the  use  of  belts 
running  in  the  solution.  The  barrel  is  removable  at  any 
time  without  throwing  off  the  belt  or  interfering  with  the 
drive.  For  raising  and  lowering  the  plating  barrel  a  lifting 
device  is  very  convenient.  Fig.  117  shows  a  hand-wheel  lift- 
ing device.  In  operation  it  raises  and  lowers  the  plating  bar- 
rel in  a  perpendicular  direction,  and  when  the  barrel  is  sus- 
pended above  the  tank  for  a  few  seconds  will  allow  the 

FIG.  117. 


solution  to  drip  directly  back  into  the  tank.  This  reduces 
the  loss  of  solution  to  a  minimum  and  overcomes  the  difficulty 
of  a  wet  and  sloppy  floor. 

In  connection  with  this  apparatus  the  use  of  patent  curved 
elliptic  anodes,  as  shown  in  the  illustration,  is  recommended. 
The  anode  is  curved  to  fit  the  periphery  of  the  revolving  bar- 
rel, and  when  an  anode  is  hung  on  each  side  of  the  tank,  the 
barrel  holding  the  work  is  equidistant  at  all  times  from  the 


"298  ELECTRO-DEPOSITION    OF    METALS. 

-anode ;  hence  a  regular  and  even  deposit  is  obtained.  These 
anodes  are  cast  in  all  metals  with  square  copper  hooks 
attached. 

The  above-described  mechanical  electro-plating  devices  are 
equally  well  adapted  for  zincking  articles  in  large  quantities, 
such  as  screws,  nails,  rivets,  etc.,  as  well  as  for  brassing, 
coppering,  etc. 

Nickeling  sheet-zinc.  The  nickeling  of  sheet-zinc  has  been 
surrounded  with  a  great  deal  of  mystery  by  those  engaged  in 
its  manufacture,  which  may,  perhaps,  be  excusable  on  the 
ground  that  there  is  scarcely  another  branch  of  the  electro- 
plating industry  in  which  experience  had  to  be  acquired  at  the 
sacrifice  of  so  much  money  and  time  as  in  this.  Nevertheless, 
the  nickeling  of  sheet-zinc  makes  no  greater  demand  on  the 
intelligence  of  the  operator  than  any  other  electro-plating  pro- 
cess, it  requiring  only  an  accurate  consideration  of  the  relations 
of  the  electric  behavior  of  zinc  towards  nickel ;  consequently, 
a  knowledge  of  the  strength  of  the  counter-current  and  of  the 
chemical  behavior  of  zinc  towards  the  nickel  solution,  which 
may  readily  dissolve  the  zinc ;  further,  a  correct  estimation  of 
the  proper  current-strength  required  for  a  determined  zinc 
surface,  as  well  as  of  the  proper  anode  surface,  and  the  most 
suitable  composition  and  treatment  of  the  nickel  baths. 

With  due  observation  of  these  conditions,  the  nickeling  of 
sheet-zinc  is  accomplished  as  readily  as  that  of  other  metals ; 
and  the  suggestions  to  first  cover  the  sheets  in  a  bath  with  a 
strong  current,  and  finish  nickeling  with  a  weaker  current, 
or  to  amalgamate  the  zinc  before  nickeling,  need  not  be 
considered. 

Below  the  conditions  required  for  nickeling  sheet-zinc,  and 
the  execution  of  the  process  itself,  together  with  the  pre- 
liminary and  final  polishing  of  the  sheets,  will  be  found  fully 
described. 

The  preliminary  grinding  or  polishing  is  effected  upon 
broad  cloth  wheels  (buffs)  formed  of  separate  pieces  of  cloth. 
The  polishing  lathes  run  with  their  points  in  movable  bear- 


DEPOSITION    OF    NICKEL    AND    COBALT.  299 

ings  secured  in  a  hanging  cast-iron  frame  by  a  set  screw  and 
safety  keys,  or  preferably  as  shown  in  Fig.  101,  since  with 
this  construction  an  injury  to  the  grinder  by  the  lathe  jump- 
ing out  is  impossible. 

The  bobs,  when  new,  have  on  an  average  a  diameter  of  12 
to  16  inches,  and  a  width  of  5J  to  8  inches.  The  principal 
point  in  the  construction  of  these  bobs  is  uniform  weight  on  all 
sides,  quiet  running  and  the  possibility  of  a  good  polish  without 
.great  exertion  depending  on  this.  Bobs  not  well  balanced  run 
unsteadily  and  jump,  thereby  producing  fine  scratches  upon 
the  sheet.  The  bobs  are  constructed  as  follows:  A  square  piece 
of  cloth  if  folded  fourfold  and  the  closed  point  cut  off  with  a 
pair  of  scissors,  so  that  on  unfolding  the  cloth,  the  hole  pro- 
duced by  the  cut  is  exactly  in  the  center  of  the  cloth  disk. 
According  to  the  diameter  of  the  spindle  more  or  less  is  cut 
away,  but  in  every  case  just  sufficient  for  the  piece  of  cloth 
to  be  conveniently  pushed  upon  the  spindle.  The  latter 
which  is  provided  with  a  pulley  and  a  hoop  against  which 
the  pieces  of  cloth  fix  themselves,  as  well  as  with  a  nut 
and  screw  for  securing  them,  is  vertically  fastened  in  a 
vise,  and  the  separate  pieces  of  cloth  are  pushed  upon  it 
so  that  the  second  piece  placed  in  position  forms  an  angle 
of  about  30°  (Fig.  118)  with  the  first,  the  operation  being 
thus  continued  until  the  bob  has  the  desired  width.  Next  a 
small,  but  very  strong  iron  disk  is  laid  upon  the  cloth  bob,  and 
the  separate  pieces  are  pressed  together  as 
firmly  as  possible  with  the  screw.  The  FIG.  118. 

spindle  is  then  placed  in  the  bearings, 
and  after  adjusting  the  belt  upon  the 
pulley  the  bob  is  revolved,  a  sharp  knife 
being  held  against  it  to  remove  the  pro- 
jecting corners.  In  polishing  sheet-zinc 
the  bobs  make  2,200  to  2,500  revolutions 
per  minute,  according  to  whether  finely 
rolled  or  rougher  sheets  are  to  be  polished. 

For   the   purpose   of  preparatory  polishing,   the   operator 


300  ELECTRO-DEPOSITION    OF    METALS. 

places  the  sheet  upon  a  support  of  hard  wood  of  the  same  size 
and  form  as  the  sheet,  and  grasps  the  two  corners  of  the  sheet 
nearest  to  his  body,  together  with  the  support,  with  the  hands, 
applying  with  the  balls  of  the  hands  the  necessary  pressure  to 
hold  the  sheet  upon  the  support.  The  lower  half  of  the  sheet, 
that  furthest  from  the  body,  rests  upon  the  knees  of  the  opera- 
tor, and  with  them  he  presses  the  sheet  against  the  polishing 
wheel,  constantly  moving  at  the  same  time,  and  at  not  too 
slow  a  rate,  the  knees  from  the  right  to  the  left,  then  from  the 
left  to  the  right,  and  so  on.  Previous  to  polishing,  a  streak 
of  oil  about  two  inches  wide  is  applied  by  means  of  a  brush 
to  the  center  of  the  sheet  in  the  visual  line  of  the  operator, 
and  the  revolving  bob  is  impregnated  with  Vienna  lime  by 
holding  a  large  piece  of  it  against  it,  when  polishing  of  the 
lower  portion  of  the  sheet  begins.  When  about  f  of  the  sur- 
face has  thus  been  polished,  the  sheet  is  turned  round  and  the 
remaining  portion  subjected  to  the  same  process.  The  sheet 
is  then  closely  inspected  to  see  whether  there  are  still  dirty  or 
dull  places,  and,  if  such  be  the  ease,  it  is  polished  once  more, 
after  moistening  it  with  some  oil  and  again  impregnating  the 
bob  with  Vienna  lime.  The  sheet  being  sufficiently  polished, 
the  oil  and  polishing  dirt  are  removed  by  dry  polishing,  after 
providing  the  bob  with  sufficient  Vienna  lime,  so  that  the 
sheets  when  finished  show  no  streaks  of  dirt  or  oil. 

Sheets  50x50,  100x50,  and  also  150x50  centimeters,  can 
in  this  manner  be  readily  polished,  but  it  is  a  difficult  feat, 
mostly  subject  to  the  risk  of  producing  bent  places,  to  polish 
sheets  6  feet  long  upon  the  knees.  Numerous  attempts  have 
therefore  been  made  to  construct  automatic  machines  for  con- 
veniently polishing  sheets  12  or  more  feet  long. 

Several  such  automatic  polishing  machines  have  been  de- 
scribed and  illustrated  in  the  fifth  edition  of  this  book,  but, 
while  they  furnish  a  quite  good  polish,  the}7  have,  on  the  one 
hand,  the  drawback  that  thin  sheets  are  readily  creased  or 
wound  around  the  polishing  roll,  and,  on  the  other  hand,  that 
the  sheets  are  with  great  violence  thrown  out  by  the  polishing 


DEPOSITION    OF    NICKEL    AND    COBALT.  30i 

roll  if  this  is  not  prevented  by  placing  another  sheet  over  a 
portion  of  the  sheet  to  be  polished,  and  passing  it  together 
with  the  latter  under  the  roll.  This,  however,  has  the  draw- 
back that  the  covered  portion  of  the  first  sheet  is  not  polished, 
#nd  has  to  be  again  passed  under  the  polishing  roll,  and  the 
place  where  the  edge  of  the  second  sheet  has  rested  upon  the 
iirst  sheet  shows  a  mark  formed  by  pressure,  which,  as  a  rule, 
is  not  desirable. 

The  polishing  machine  constructed  according  to  the  patent 
of  Hille  and  Muller  *  avoids  the  above-mentioned  drawbacks 
by  obliquely  standing  polishing  rolls.  In  KofHer's  f  construc- 
tion two  polishing  rolls  move  in  opposite  directions.  The 
sheets  are  pressed  against  the  rolls  by  an  oscillating  table  so 
that  first  one  and  then  the  other  portion  of  the  table  is  alter- 
nately advanced  towards  the  corresponding  polishing  roll. 

In  the  construction  patented  by  Dr.  Langbein  &  Co.,  the 
drawbacks  of  throwing  out  and  crumpling  the  sheets  is  over- 
come by  the  arrangement  of  two  polishing  bobs,  which  alter- 
nately stand  still  and  revolve,  however,  in  opposite  directions. 
The  table  consists  of  two  movable  halves ;  while  one  of  the 
halves,  in  an  elevated  position,  presses  the  sheet  carried  by  the 
transport-rolls  against  the  revolving  polishing  bob,  the  other 
half  is  lowered  and  its  polishing  bob  remains  stationary. 
When  a  certain  length  of  the  sheet  has  been  polished  the 
second  polishing  bob  revolving  in  an  opposite  direction  is  put 
in  action,  a  constant  stretching  of  the  sheet  being  thereby 
-effected. 

Freeing  zinc  sheets  from  grease.  This  is  best  effected  in  two 
•operations,  first  dry  and  then  wet.  For  the  dry  process  use  a 
very  soft  piece  of  cloth  and,  after  dipping  it  in  Vienna  lime, 
very  finely  pulverized  and  passed  through  a  hair  sieve,  rub 
over  the  sheet  in  the  direction  of  a  right  angle  to  the  polishing 
streaks,  applying  a  very  gentle  pressure.  For  the  wet  process, 
•dip  a  moist  piece  of  cloth,  or  a  soft  sponge  free  from  sand,  into 

*  German  patent,  49736.  t  German  patent,  89648. 


302  ELECTRO-DEPOSITION    OP    METALS. 

a  paste  of  impalpable  Vienna  lime,  whiting  and  water,  and  go- 
carefully  over  the  sheet  so  that  no  place  remains  untouched. 
Then  rinse  the  sheet  under  a  powerful  jet  of  water,  best  under 
a  rose,  being  particularly  careful  to  remove  all  the  lime,  going 
over  the  sheet,  if  necessary,  with  a  soft,  wet  rag,  and  observ- 
ing whether  all  parts  appear  evenly  moistened.  If  such  be 
the  case,  cleaning  is  complete,  otherwise  the  sheet  has  to  be 
once  more  treated  with  lime. 

If  the  sheets  are  to  be  nickeled  on  only  one  side,  two  of  them 
are  placed  together  with  their  unpolished  sides  and  fastened  on 
the  two  upper  corners  with  binding  screws  to  which  is  soldered 
a  copper  strip  about  0.39  inch  wide,  by  which  they  are  sus- 
pended to  the  conducting  rods.  Plating  is  then  at  once  pro- 
ceeded with,  without  allowing  the  sheets  to  remain  exposed 
to  the  air  longer  than  is  absolutely  necessary.  Special  care 
must  be  had  that  the  lime  does  not  dry,  as  this  would  produce 
stains. 

With  sheets  50  x  50  centimeters,  two  binding  screws  suffice 
for  suspending  the  sheets  to  the  conducting  rods.  With  sheets 
100  centimeters  long,  three  binding  screws  are  generally  used, 
with  sheets  150  centimeters  long,  five,  and  with  lengths  of 
200  centimeters,  six  or  more,  so  that  the  curre.nt  required  for 
nickeling  finds  a  sufficient  cross-section. 

Some  manufacturers  nickel  the  cleansed  sheet  without  pre- 
vious coppering  or  brassing,  and  claim  special  advantages  for 
such  direct  nickeling.  This  may  be  done  with  a  bath  of  nickel 
sulphate  and  potassium  citrate  without,  or  with  a  greater  or 
smaller,  addition  of  ammonium  chloride,  according  to  the 
surface  to  be  nickeled  and  the  intensity  of  current  at  disposal. 
However,  sheet-zinc  directly  nickeled  does  not  show  the  warm, 
full  tone  of  sheets  previously  coppered  or  brassed  ;  besides, 
direct  nickeling  requires  a  far  more  powerful  current,  so  that 
it  is  not  even  more  economical. 

For  the  nickeling  process  itself,  it  is  indifferent  whether  the 
sheets  are  previously  coppered  or  brassed,  but  the  choice  be- 
tween the  two  is  controlled  by  a  few  features  which  must  be 


DEPOSITION    OF    NICKEL    AND    COBALT.  SOS 

mentioned.  The  nickel  deposit  upon  brassed  sheets  shows  a 
decidedly  whiter  tone  than  that  upon  coppered  sheets,  and 
brassing  would  deserve  the  preference  if  this  process  did  not 
require  extraordinarily  great  care  in  the  proper  treatment  of 
the  bath,  the  nickel  deposit  readily  peeling  off,  generally  in  the 
bath  itself,  which  seldom  or  never  occurs  with  coppered  sheet, 
and  then  may  generally  be  considered  due  to  insufficient, 
cleaning  or  other  defective  manipulation. 

This  peeling-off  of  the  nickel  deposit  may  be  prevented  by 
giving  due  consideration  to  the  conditions  and  avoiding,  on  the 
one  hand,  too  large  an  excess  of  potassium  cyanide  in  the  brass 
bath,  and,  on  the  other,  by  regulating  the  current  so  that  no- 
pale  yellow  or  greenish  brass  is  precipitated.  Since  nickeling 
with  a  strong  current  requires  only  a  few  minutes  for  a  deposit 
of  sufficient  thickness  capable  of  bearing  polishing,  it  is  gener- 
ally desired  to  brass  the  sheets  at  the  same  time,  so  that  the 
operation  may  proceed  rapidly  and  continuously.  To  do  this, 
a  very  powerful  current  has  to  be  conducted  into  the  brass  bath, 
the  result  being  that  a  deposit  with  a  larger  content  of  zinc- 
and  a  correspondingly  lighter  color  is  formed,  but  also  with  a 
coarser,  less  adherent  structure,  and  this  is  the  principal  reason 
why  the  nickel  deposit,  together  with  the  brass  deposit,  peels- 
off.  To  avoid  this,  the  brassing  must  be  done  with  a  current 
so  regulated  that  the  deposit  precipitates  uniformly,  adheres 
firmly,  and  is  not  porous ;  the  correct  progress  of  the  operation 
is  recognized  by  the  color  being  more  like  tombac,  and  not 
pale  yellow  or  greenish.  When  brassing  has  to  be  done  quickly 
the  content  of  copper  in  the  brass  bath  must  be  increased  to 
such  an  extent  that  a  powerful  current  produces  a  deposit  of 
the  above-mentioned  color,  and,  hence,  too  large  an  excess  of 
potassium  cyanide  must  be  strictly  avoided. 

It  will  be  seen  that  brassing  requires  a  certain  attention 
which  is  not  necessary  in  coppering,  and  therefore  the  latter 
is  to  be  preferred. 

For  coppering,  one  of  the  baths,  formulas  III  to  VII,  given 
under  "  Deposition  of  Copper  "  can  be  used,  to  which,  for  this 


304  ELECTRO-DEPOSITION    OF    METALS. 

special  purpose,  more  potassium  cyanide  may  be  added.  The 
sheets  should  remain  in  this  bath  no  longer  than  required  to 
uniformly  coat  them  with  a  beautiful  .red  layer  of  copper,  and 
under  no  circumstances  must  they  be  allowed  to  remain  until 
the  coppering  commences  to  become  dull  or  even  discolored. 
They  should  come  from  the  bath  with  a  full,  or  at  least  half, 
luster. 

When  taken  from  the  copper  bath  the  sheets  are  thoroughly 
rinsed  in  a  large  water  reservoir,  the  contents  of  which  must 
be  frequently  renewed,  care  being  had  to  remove  any  copper 
solution  adhering  to  the  unpolished  sides  which  are  not  to  be 
nickeled,  since  that  would  soon  spoil  the  nickel  bath.  The 
sheets  are  then  immediately  brought  into  the  nickel  bath,  it 
being  best  to  suspend  two,  three,  or  four  of  them  at  the  same 
time,  to  prevent  one  from  being  more  thickly  nickeled  than 
the  other,  and  take  them  out  the  same  way.  In  suspending 
the  sheets  in  the  bath,  care  should  be  had  to  bring  them  as 
soon  as  possible  in  contact  with  the  conducting  rod,  a  neglect 
of  this  rule  being  apt  to  produce  blackish  streaks  and  stains. 

The  tanks  used  for  nickeling  sheet-zinc  are  generally  about 
"7  feet  long  in  the  clear,  1J  feet  wide,  and  2J  to  2J  feet  deep. 
In  such  tanks  sheets  6J  feet  long  and  1J  feet  wide  can  be 
-conveniently  nickeled. 

With  the  use  of  a  nickel  bath  according  to  formula  VIII,  p. 
258,  for  nickeling  sheet-zinc,  the  most  suitable  electro-motive 
force  is  3.5  volts  and  1  ampere  current-density  per  square  deci- 
meter, in  order  to  obtain  in  three  minutes  an  effective  deposit. 
After  working  for  some  time  this  bath  also  requires  a  stronger 
•electro-motive  force. 

If  zinc  is  to  be  nickeled  in  baths  conducting  with  greater 
difficulty,  for  instance,  in  a  simple  solution  of  nickel-ammo- 
nium sulphate  without  the  addition  of  conducting  salts,  or  in 
baths  containing  boric  acid,  1.2  to  1.5  amperes  and  7  volts 
must  be  allowed  for  1  square  decimeter,  if  nickeling  is  to  be 
•effected  in  the  above-mentioned  space  of  time. 

For  nickeling  sheet-zinc,  rolled  anodes  are,  as  a  rule,  only 


DEPOSITION    OF    NICKEL    AND    COBALT.  305 

used,  except  when  working  with  baths  containing  joric  acid. 
The  anode  surface  must  at  least  be  equal  to  that  of  the  zinc 
surface.  The  distance  between  the  anodes  and  the  sheets 
should  be  from  3  to  3f  inches,  and  when  the  current-strength 
is  somewhat  scant  the  distance  may  be  reduced  to  2|  inches. 
The  nickel  anodes  have  to  be  taken  from  the  bath  once  daily 
and  scoured  bright  with  scratch-brushes  and  sand.  For  the 
rest,  all  the  rules  given  for  nickel  anodes  are  valid. 

Baths  used  for  nickeling  sheet-zinc  soon  become  alkaline  in 
•consequence  of  the  powerful  current  used,  which  is  shown  by 
red  litmus-paper  turning  blue.  The  alkalinity  also  manifests 
itself  by  the  bath  becoming  turbid  and  the  nickeling  not  turn- 
ing out  pure  white.  The  slightly  acid  reaction  required  is  re- 
stored by  citric  acid  solution.  The  appearance  of  the  dreaded 
>black  streaks  and  stains  is  due  either  to  the  current  itself  being 
too  weak,  or  to  its  having  been  weakened  by  an  extremely 
great  resistance  of  the  nickel  bath  ;  also  to  an  insufficient  me- 
tallic surface  of  the  anodes,  which  may  be  either  too  small  or 
not  sufficiently  metallic  on  account  of  tarnishing ;  and  finally 
to  an  excessive  alkalinity  of  the  bath,  or  insufficient  contact 
of  the  hooks  with  the  connecting  rods. 

The  metallic  content  of  the  bath  must  from  time  to  time  be 
strengthened  by  the  addition  of  nickel  salt,  and  the  bath 
filtered  at  certain  intervals.  When  the  conductivity  abates, 
it  has  to  be  restored  by  the  addition  of  conducting  salts. 

When  the  sheets  have  been  sufficiently  nickeled,  they  are 
allowed  to  drain  off,  then  plunged  into  hot  water,  and,  after 
removing  the  binding  screws,  dried  by  gentle  rubbing  with 
fine  sawdust  free  from  sand  and  passed  through  a  fine  sieve 
to  separate  pieces  of  wood.  In  all  manipulations,  the  un- 
nickeled  sides  are  placed  together,  while  a  piece  of  paper  of  the 
size  and  form  of  the  sheets  is  laid  between  the  nickeled  sides. 

The  nickeled  sheets  are  finally  polished,  which  is  effected 
by  placing  them  upon  supports  and  pressing  against  the 
revolving  bob  as  previously  described,  the  sheets  being,  how- 
ever, only  moderately  moistened  with  oil,  and  not  too  much 
20 


306  ELECTRO-DEPOSITION    OF    METALS. 

Vienna  lime  applied  to  the  bob.  Polishing  is  done  first  ia 
one  direction  and  then  in  another,  at  a  right  angle  to  the  first. 
After  polishing,  the  sheets  are  finally  cleansed  with  a  piece  of 
soft  cloth  and  impalpable  Vienna  lime,  when  they  should 
show  a  pure  white  lustrous  nickeling,  free  from  cracks  and 
stains,  and  bear  bending  and  rebending  several  times  without 
the  deposit  of  nickel  breaking  or  peeling  off. 

Nickeling  tin-plate. — For  handsome  and  durable  nickeling,, 
tin-plate  also  requires  previous  coppering.  Deposition  is 
effected  with  a  less  powerful  current  than  for  sheet-zinc. 
Freeing  from  grease  is  done  in  the  same  manner  as  above- 
described. 

For  preparatory  polishing  of  tin-plate,  the  use  of  a  polish- 
ing compound  free  from  lime  and  grease  is  recommended,, 
since  a  good  polish  on  tin  cannot  be  obtained  with  Vienna 
lime  and  oil.  Nickeled  tin-plate  may  be  polished  with  Vienna 
lime  and  stearine  oil. 

It  may  be  here  mentioned  as  a  remarkable  fact  that  freshly 
nickeled  tin-plate  will  stand  every  kind  of  manipulation,  such 
as  stamping,  edging,  pressing,  etc.,  but  after  having  been 
stored  for  a  few  months,  the  layer  of  nickel  frequently  peels- 
of  by  these  operations. 

Nickeling  copper  and  brass  sheets. — The  treatment  of  these 
sheets  differs  from  that  of  sheet-zinc  in  that  the  rough  sheets 
are  first  brushed  with  emery  and  then  polished  with  the  bob. 

After  treating  the  sheets  with  hot  caustic  lye  or  lime-paste,, 
they  are  pickled  by  brushing  them  over  with  a  solution  of  1 
part  of  potassium  cyanide  in  20  parts  of  water.  They  are  then 
thoroughly  and  rapidly  rinsed,  and  immediately  brought  into- 
the  bath.  To  avoid  peeling  off,  the  current-density  should 
not  exceed  0.4  ampere. 

Nickeling  sheet-iron  and  sheet-steel. — Only  the  best  quality 
of  sheet  should  be  used  for  this  purpose.  After  rolling,  the- 
sheets  are  freed  from  scales  by  pickling,  then  passed  through 
the  fine  rolls,  and  finally  again  pickled.  If  the  nickeled  sheets- 
are  not  to  exhibit  a  high  degree  of  polish,  it  suffices  to  brush 


DEPOSITION    OF    NICKEL    AND    COBALT.  307 

them  before  nickeling  with  a  large,  broad  fiber  brush  (p.  204) 
and  emery  No.  00.  But  for  a  high  luster,  such  as  is  generally 
demanded,  the  sheets  have  first  to  be  ground.  For  fine-grind- 
ing the  pickled  sheets,  broad,  massive  wood  rolls,  turned  and 
directly  glued  with  emery  are  used.  These  wheels  are  10  to  12 
inches  in  diameter,  and  2  to  4  or  more  inches  long,  according 
to  the  size  of  the  sheets.  For  the  first  grinding,  the  wheels  are 
coated  with  glue  and  rolled  in  emery  No.  100  to  120,  according 
to  the  condition  of  the  sheets,  while  emery  No.  00  is  applied 
to  the  wheels  used  for  the  fine  grinding.  The  grinding  is 
succeeded  by  brushing,  as  described  on  page  205. 

After  preparing  a  sufficiently  smooth  surface,  the  sheets  are 
at  once  rubbed  with  a  rag  moistened  with  petroleum,  or,  if 
preferred,  with  a  rag  and  pulverized  Vienna  lime.  They  are 
then  scoured  wet  in  the  manner  described  for  sheet-zinc.  The 
scouring  material  must  be  liberally  applied,  especially  if  the 
sheets  are  to  be  directly  nickeled  without  previous  coppering, 
the  latter  being,  however,  quite  advisable.  After  rinsing  off 
the  lime-paste,  the  sheets  are  without  loss  of  time  brought  into 
the  nickel  bath. 

For  nickeling,  a  bath  free  from  chlorine  should  by  all  means 
be  used  in  order  to  protect  the  sheets  from  rusting.  The 
current-density  should  be  0.4  ampere,  with  which  the  sheets 
acquire  in  f  hour  a  deposit  of  sufficient  thickness.  With  the 
use  of  cold,  quick  nickeling  baths  the  same  thickness  of  the 
deposit  may  be  obtained  in  15  minutes.  It  is  not  advisable  to 
attempt  to  obtain  a  heavy  deposit  in  a  shorter  time,  because  it 
would  lack  density  which,  by  reason  of  greater  protection 
against  rust,  is  the  principal  requisite  for  nickeled  sheet-iron. 

After  nickeling,  the  sheets  are  rinsed  in  clean  water,  then 
plunged  into  hot  water,  and  dried  by  rubbing  with  warm  saw- 
dust. After  this  operation,  it  is  recommended  to  thoroughly 
dry  the  sheets  in  an  oven  heated  to  between  176°  to  212°  F., 
to  expel  any  moisture  from  the  pores,  and  then  to  polish  them 
with  Vienna  lime  and  oil,  or  with  rouge. 

Nickeling  wire.     Nickeling  of  wire  of  iron,  brass  or  copper 


308  ELECTRO-DEPOSITION    OF    METALS. 

is  scarcely  ever  done  on  a  large  scale.  It  is,  however,  believed 
that  the  nickeling  of  iron  and  steel  wires — for  instance,  piano- 
strings — might  be  of  advantage  to  prevent  rust,  or  at  least  to 
retard  the  commencement  of  oxidation  as  long  as  possible. 

To  nickel  single  wires  cut  into  determined  lengths,  accord- 
ing to  the  general  rules  already  given,  is  simple  enough  ;  but 
this  method  cannot  be  pursued  with  wire  several  hundred 
yards  long,  rolled  in  coils,  as  it  occurs  in  commerce.  Nickel- 
ing the  wire  in  coils,  however,  cannot  be  done,  as  only  the 
upper  windings  exposed  to  the  anodes  would  acquire  a  coat 
of  nickel.  Hence  it  becomes  necessary  to  unwind  the  coil,  and 
for  continuous  working  pass  the  wire  at  a  slow  rate  through 
the  cleansing  and  pickling  baths,  as  well  as  the  nickel  bath, 
and  hot  water  reservoir,  as  shown  in  Fig.  119,  in  cross-section, 
and  in  Fig.  120,  in  ground  plan. 

The  unwinding  of  the  wire  is  effected  by  a  slowly  revolving 
shaft,  upon  which  the  nickeled  wire  again  coils  itself;  but  in 
the  illustration  the  shaft  is  omitted.  In  Fig.  120  four  wires  run 
over  the  four  rolls  a,  mounted  upon  a  common  shaft,  to  the 
rolls  b  upon  the  bottom  of  the  tank  A,  whereby  they  come  in 
contact  with  a  thickly-fluid  lime-paste  in  the  vat,  and  are  freed 
from  grease.  From  the  rolls  b  the  wires  run  through  the 
wooden  cheeks  i,  lined  with  felt,  which  retain  the  excess  of 
lime-paste,  and  allow  it  to  fall  back  into  the  tank.  The  wires 
then  pass  over  the  roll  c  to  the  roll  d.  Between  these  two  rolls 
is  the  rose  g,  which  throws  a  powerful  jet  of  water  upon  the 
wires,  thereby  freeing  them  from  adhering  lime-paste.  The 
roll  d,  as  well  as  its  axis,  is  of  brass,  and  to  the  latter  is  con- 
nected the  negative  pole  of  the  battery  or  dynamo,  so  that  by 
carrying  the  wires  over  the  roll  d,  negative  electricity  is  con- 
ducted to  them.  From  the  roll  d,  the  wires  run  over  the  roll- 
bench  s  (Fig.  119)  to  the  tank  C,  which  contains  the  nickel 
solution,  so  that  they  are  subjected  to  the  action  of  the  anodes 
arranged  in  this  tank  on  both  sides  of  the  wires.  The  wires 
then  pass  over  the  roll  e,  are  rinsed  under  the  rose  h,  and  run 
finally  through  a  hot-water  reservoir  and  sawdust  (these  two 


DEPOSITION    OP    NICKEL    AND    COBALT. 


309 


apparatuses  are  not  shown   in  the  illustration),  to  be  again 
wound  in  coils.     In  case  a  high  polish  is  required,,  the  nick- 


eled  wires  may  be  run  under  pressure  through  leather  cheeks 
dusted  with  Vienna  lime. 


310  ELECTRO-DEPOSITION    OF    METALS. 

Nickeling  knife-blades,  sharp  surgical  instruments,  etc.  Con- 
siderable trouble  is  frequently  experienced  in  nickeling  sharp- 
•edged  instruments,  the  edges  and  points  being  spoiled  either 
by  the  deposit  of  nickel  or  in  polishing.  And  yet  such  instru- 
ments can  be  readily  nickeled  in  such  a  manner  that  the 
edges  remain  in  as  good  condition  as  before. 

If  new  instruments  which  have  never  been  used  are  to  be 
nickeled,  no  special  preparation  is  required,  it  being  only  nec- 
essary to  free  them  at  once  from  grease  and  bring  them  into 
the  bath.  But  instruments  which  have  been  used  or,  by  bad 
treatment  have  become  partly  or  entirely  covered  with  rust, 
must  be  first  freed  from  rust  by  chemical  or  mechanical  treat- 
ment, and  then  polished.  The  marks  left  by  the  stone  or 
emery  wheel  are  effaced  by  means  of  the  circular  brush,  this 
treatment  being  necessary  to  obtain  perfect  nickeling.  But, 
in  brushing,  the  edges  are  rendered  dull  if  special  precaution- 
ary measures  are  not  used.  For  instance,  the  edge  of  a  knife- 
blade  must  never  come  in  contact  with  the  brush.  This  is 
prevented  by  firmly  pressing  the  blade  flat  upon  a  soft  sup- 
port of  felt  or  cloth,  so  that  the  edge  sinks  somewhat  into  the 
support,  without,  however,  cutting  into  it.  The  edge  is  then 
held  downward,  and  thus  together  with  the  support  brought 
against  the  revolving  brush.  In  this  manner  the  blades  may 
be  vigorously  brushed  without  fear  of  spoiling  the  edges. 

The  treatment  for  giving  them  a  high  polish  after  nickeling 
is  the  same.  Freeing  from  grease  may  be  done  in  the  usual 
manner  with  lime-paste ;  but  must  also  be  effected  upon  a  soft 
support,  the  same  as  in  polishing.  After  thorough  rinsing  in 
clean  water,  the  separate  pieces,  without  being  previously  cop- 
pered, are  brought  directly  into  the  nickel  bath,  the  composi- 
tion of  which  must,  of  course,  be  suitable  for  nickeling  steel 
articles.  The  instruments  are  first  coated  with  the  use  of  a 
strong  current,  so  that  deposition  takes  place  slowly  and  with 
great  uniformity. 

In  suspending  the  articles  in  the  bath,  care  should  be  had 
that  neither  a  point  nor  an  edge  is  turned  towards  the  anodes. 


DEPOSITION    OF    NICKEL    AND    COBALT.  311 

It  is  best  to  use  a  bath  with  anodes  on  one  side  only,  and  to 
suspend  the  blades  with  their  backs  towards  the  anodes.  If, 
for  any  reason,  the  instruments  are  to  be  suspended  between 
two  rows  of  anodes,  the  edges  should  be  uppermost,  as  near  as 
possible  to  the  level  of  the  bath  ;  but  they  should  never  hang 
deep  or  downwards. 

These  precautionary  measures  may  be  omitted  by  using  for 
nickeling  such  articles  with  sharp  edges,  the  bath  consisting  of 
nickel  sulphate  and  sodium  citrate,  which  has  been  previously 
mentioned.  In  this  bath,  the  edges  and  points  of  the  instru- 
ments do  not  burn  as  readily  as  in  olher  nickel  baths,  and  the 
deposited  nickel  being  soft,  it  does  not  show  a  tendency  to 
peeling  off  when,  after  nickeling,  the  edges  of  the  instruments 
are  sharpened. 

The  plated  instruments  are  given  a,fmer  luster  by  polishing, 
but  during  this  operation  they  must  always  be  exposed  upon 
a  soft  support,  as  above  described,  to  the  action  of  a  felt  wheel, 
or,  still  better,  of  a  cloth  bob. 

In  nickeling  skates  it  is  advisable  to  suspend  them  so  that 
the  runners  hang  upwards  and  that  the  running  surfaces  are 
level  with  the  surface  of  the  bath,  because  if  the  deposit  upon 
the  running  surfaces  is  too  thick,  it  peels  off  readily  when 
injured  by  grains  of  sand  upon  the  ice. 

Nickeling  of  soft  alloys  of  lead  and  tin,  with  or  without  addi- 
tion of  antimony,  as  are  used  for  siphon-heads,  etc.,  is  effected, 
in  case  the  objects  have  already  a  high  luster,  by  freeing  them 
from  grease  with  whiting  and  a  small  quantity  of  Vienna  lime, 
then  rinsing  in  water,  lightly  coppering,  or  better,  brassing, 
and  finally  nickeling  in  a  bath  containing  chlorine. 

If  the  objects  require  preparatory  polishing,  use  a  polishing 
compound  free  from  lime  and  grease,  as  given  under  nickeling 
of  tin-plate,  rinse  with  benzine,  immerse  in  hot  water,  and  free 
from  grease  with  whiting  and  Vienna  lime.  Then  brass, 
nickel  and  polish.  Direct  nickeling  without  previous  brass- 
ing is  not  advisable,  waste  in  consequence  of  peeling  off  being 
frequently  the  result. 


312  ELECTRO-DEPOSITION    OF    METALS. 

Nickeling  printing  plates  (stereotypes,  cliches,  etc.).  The  ad- 
vantages of  nickeling  stereotypes,  etc.,  over  steeling  will  be 
referred  to  under  "  Steeling,"  and  hence  only  the  most  suit- 
able composition  of  the  nickel  baths  and  the  manipulation, 
required  will  here  be  given. 

The  nickel  baths  according  to  formula  I  (page  253)  and 
formula  VII  (page  257)  are  the  most  suitable  for  simple 
nickeling,  because  the  ammonium  sulphate  not  being  present 
in  too  great  an  excess,  as  well  as  the  presence  of  boric  acid,, 
causes  the  nickel  to  separate  with  considerable  hardness. 
With  nickeled  stereotypes  three  times  as  large  an  edition, 
can  be  printed  as  with  plates  of  the  same  material  not 
nickeled. 

Hard  nickeling.  It  being  a  well-known  fact  that  a  fused 
alloy  of  nickel  with  cobalt  possesses  greater  hardness  than 
either  of  the  metals  by  themselves,  experiments  proved  that 
an  electro-deposited  nickel-cobalt  alloy  exhibited  the  same  be- 
havior, the  greatest  degree  of  hardness  being  attained  with  an 
addition  of  cobalt  varying  between  25  and  30  per  cent.  For 
this  deposit  the  term  hard  nickeling  is  proposed,  the  most  suit- 
able bath  for  the  purpose  being  .prepared  according  to  the- 
following  formula  : 

Nickel-ammonium  sulphate  21.16  ozs.,  cobalt-ammonium 
sulphate  5.29  ozs.,  crystallized  boric  acid  8.8  ozs.,  water  10  to 
12  quarts. 

To  prepare  the  bath  dissolve  the  constituents  by  boiling 
as  given  under  formula  VII,  p.  257.  In  case  the  metal  salts- 
should  contain  free  acids  add,  previous  to  the  addition  of  the 
boric  acid,  a  small  quantity  of  nickel  carbonate.  The  boric- 
acid  must  not  be  neutralized  and  the  bath  should  work  with 
its  acid  reaction.  Mixed  anodes  in  the  proportion  of  ^  cast 
and  f  rolled,  are  to  be  suspended  in  the  bath. 

The  bath  prepared  according  to  formula  No.  II  deserves  the- 
preference,  it  yielding  a  harder  deposit  than  bath  No.  I. 

For  the  rest,  the  treatment  of  the  baths  is  the  same  as  that 
given  for  nickel  baths  of  similar  composition  (pp.  253  and] 


DEPOSITION    OF    NICKEL    AND    COBALT. 


313 


257),  and  the  process  of  hard  nickeling  does  not  essentially 
differ  from  ordinary  nickeling.  The  suspending  hooks  are 
soldered  to  the  backs  of  the  plates  by  means  of  the  soldering- 
iron  and  a  drop  of  tin  ;  or  the  plates  are  secured  in  holders 
of  sheet-copper  0.11  inch  thick,  and  {  to  1  inch  wide,  of  the 
form  shown  in  Fig.  121.  The  printing  surface  is  freed  from 
grease  by  brushing  with  lime-paste,  rinsing  in  water,  and  then 
brushing  with  a  clean  brush  to  remove  the  lime  from  the 
depressions.  The  plates  are  then  hung  in  the  bath  and 

FIG.  121. 


covered  with  a  strong  current.  When  everywhere  coated 
with  nickel,  the  current  is  weakened  and  the  deposit  allowed 
gradually  to  augment.  With  an  average  duration  of  nickel- 
ing of  15  to  20  minutes,  with  2.8  to  3  volts,  the  deposit  will, 
as  a  rule,  be  sufficiently  resisting. 

Stereotypes  of  type  metal,  after  being  freed  from  grease,  are 
best  lightly  coppered  in  the  acid  copper  bath,  then  rinsed  and 
brought  into  the  nickel  bath.  Zinc  etchings  are  first  coppered, 
not  too  slightly,  in  the  copper  cyanide  bath,  rinsed,  and  sus- 


;314  ELECTRO-DEPOSITION    OF    METALS. 

pended  in  the  nickel  bath  with  a  very  strong  current.  With 
•too  weak  a  current,  black  streaks  are  formed,  zinc  is  dissolved, 
and  both  the  plate  and  bath  are  spoiled.  With  copper  elec- 
tros, pickling  with  potassium  cyanide  solution,  after  freeing 
-from  grease,  must  not  be  omitted. 

The  nickeled  plates  are  rinsed  in  water,  then  plunged  in 
hot  water,  and  dried  in  sawdust,  when  the  nickeled  printing 
surface  may  be  brushed  over  with  a  brush  and  fine  whiting,  it 
being  claimed  that  plates  thus  treated  take  printing  ink  better, 
while  the  first  impressions  of  plates  not  brushed  with  whiting 
are  somewhat  dull. 

Nickel-facing   is   especially  suitable   for   copper   plates  for 
-color-printing,  the  nickel  not  being  attacked  like  copper  or 
iron  by  cinnabar. 

Recovery  of  nickel  from  old  baths.  At  the  present  price  of 
nickel  its  recovery  from  old  solutions  scarcely  pays.  The  ineffi- 
ciency of  the  bath  is  in  most  cases  due  to  two  causes :  It  has 
either  become  too  poor  in  metal  or  it  contains  foreign  metallic 
-admixtures.  In  the  first  case,  the  expense  of  evaporating,  to- 
.gether  with  the  further  manipulations,  is  out  of  proportion  to 
the  value  of  the  nickel  recovered,  and,  in  the  second  case,  the 
reduction  of  the  foreign  metals  is  inconvenient  and  connected 
with  expense  which  make  it  unprofitable.  The  recovery  of 
nickel  from  old  baths  which  have  become  useless,  by  the  elec- 
tric current  with  the  use  of  carbon-plate  anodes,  as  here  and 
there  recommended,  is  the  most  disastrous  and  expensive  of 
-all,  and  can  only  be  condemned. 

For  nickeling  by  contact  and  boiling,  see  special  chapter, 
'"  Depositions  by  Contact." 

Deposition  of  nickel  alloys. — From  suitable  solutions  of  the 
metallic  salts  nickel  may  be  deposited  together  with  copper 
and  tin,  as  well  as  with  copper  and  zinc.  With  the  first 
•combination,  especially,  all  tones  from  copper- red  to  gold- 
shade  may  be  obtained,  according  to  which  metal  predomi- 
nates, or  according  to  the  current-strength  which  is  conducted 
into  the  bath,  as  is  also  the  case  in  brassing. 


DEPOSITION    OF    NICKEL    AND    COBALT.  315 

A  suitable  bath  for  coating  metallic  articles  with  an  alloy 
•of  nickel,  copper  and  tin,  for  which  the  term  nickel-bronze  is 
proposed,  is  obtained  by  dissolving  the  metallic  phosphates  in 
sodium  pyrophosphate  solution.  By  mixing  solution  of  blue 
vitriol  with  solution  of  sodium  phosphate,  cupric  phosphate  is 
precipitated,  which  is  filtered  off  and  washed.  In  the  same 
•manner  nickel  phosphate  is  prepared  from  a  solution  of  nickel 
sulphate.  These  phosphates  are  then,  each  by  itself,  dis- 
solved in  a  concentrated  solution  of  sodium  pyrophosphate, 
while  chloride  of  tin  is  directly  dissolved  in  sodium  pyro- 
phosphate until  the  turbidity,  at  first  rapidly  disappearing, 
disappears  but  slowly. 

Nothing  definite  can  be  said  in  regard  to  the  mixing  pro- 
portions of  these  three  solutions,  because  the  proportions  will 
/have  to  be  varied  according  to  the  desired  color  of  the  de- 
posit. The  operator,  however,  will  soon  find  out,  of  which 
solution  more  has  to  be  added  to  obtain  the  tone  desired. 

For  depositing  a  nickel-copper-zinc  alloy  solutions  of  cupric 
sulphate  (blue  vitriol)  and  zinc  oxide  in  potassium  cyanide 
to  which  is  added  an  ammoniacal  solution  of  nickel  carbonate, 
may  be  advantageously  used.  As  will  be  seen  a  deposit  of 
German  silver  can  be  obtained  with  the  use  of  this  solution  if 
the  latter  contains  the  metals  in  the  same  proportions  as 
^German  silver,  and  German  silver  anodes  are  used. 

According  to  a  French  process,  a  deposit  of  German  silver 
may  be  obtained  as  follows  :  Dissolve  a  good  quality  of  Ger- 
man silver  in  nitric  acid  and  add,  with  constant  stirring, 
solution  of  potassium  cyanide  until  all  the  metal  is  precipitated 
as  cyanide.  The  precipitate  is  then  filtered  off,  washed,  dis- 
solved in  potassium  cyanide,  and  the  solution  diluted  with 
double  the  volume  of  water.  This  process,  however,  does  not 
seem  very  feasible,  since  nickel  separates  with  difficulty  from 
its  cyanide  combination. 


316  ELECTRO-DEPOSITION  OF  METALS. 

EXAMINATION  OF  NICKEL  BATHS. 

The  reaction  of  the  nickel  baths  have  previously  been 
briefly  referred  to,  but  the  subject  must  here  be  more  closely 
considered. 

For  the  determination  of  the  content  of  acid,  a  different 
method  must  be  adopted  according  to  the  composition  of  the 
bath,  i.  e.,  whether  it  has  been  prepared  with  an  addition  of 
citric  acid,  boric  acid,  etc.  The  reddening  of  blue  litmus- 
paper  simply  indicates  the  presence  of  free  acid  in  the  bath, 
but  leaves  us  in  the  dark  as  to  which  acid  is  present,  and  as 
to  its  derivation. 

If,  for  instance,  in  consequence  of  insufficient  solution  of 
nickel,  free  sulphuric  acid  appears  on  the  anodes,  the  bath  be- 
"  comes  at  the  same  time  poorer  in  nickel  in  proportion  to  the 
increase  in  the  content  of  free  sulphuric  acid.  If  we  have  to- 
deal  with  a  bath  prepared  from  nickel-ammonium  sulphate  with 
an  addition  of  ammonium  sulphate,  but  without  organic  acidsr 
the  reddening  of  blue  litmus-paper  will  at  once  indicate  a  con- 
tent of  free  sulphuric  acid,  if  the  bath  was  neutral  in  the  begin- 
ning. It  is,  however,  quite  a  different  matter  when  a  bath  con- 
taining boric  acid  is  examined.  In  the  formula)  for  preparing 
these  baths,  it  has  been  seen  that  before  adding  the  boric  acid, 
any  free  sulphuric  acid  of  the  nickel  salt  present  is  to  be  re- 
moved by  treating  the  solution  with  nickel  carbonate  or  nickel 
hydrate.  After  adding  the  boric  acid,  blue1  litmus-paper  is 
strongly  reddened,  and  this  acidity  due  to  the  boric  acid  is  to 
be  maintained  in  the  bath.  However,  in  consequence  of  the 
use  of  too  large  a  number  of  cast  anodes,  free  sulphuric  acid 
may  form  in  the  bath,  and  this,  together  with  boric  acid,  can- 
not be  recognized  by  blue  litmus-paper,  since  both  acids  red- 
den it.  In  this  case  red  congo  paper,  which  is  not  changed 
by  boric  acid,  but  is  turned  blue  by  sulphuric  acid,  has  to  be 
used.  If  red.  congo  paper  is  colored  blue,  it  is  a  sure  proof 
that,  besides  boric  acid,  free  sulphuric  acid  is  present,  which 
has  to  be  neutralized  for  the  bath  to  work  in  a  correct 
manner. 


DEPOSITION    OF    NICKEL    AND    COBALT.  317 

The  process  is  again  different  when  a  bath  prepared  with 
.an  addition  of  citric  acid  is  to  be  examined.  This  organic 
acid  colors  certain  varieties  of  commercial  congo  paper  blue, 
just  as  sulphuric  acid  does,  and  hence  tropaeolin  paper  has  to 
be  used,  which  is  not  altered  by  citric  acid,  but  is  colored 
violet  by  free  sulphuric  acid. 

If  a  nickel  bath  has  been  prepared  with  the  addition  of 
organic  salts,  for  instance,  sodium  citrate,  ammonium  tartrate 
or  others,  the  formation  of  free  sulphuric  acid  in  the  bath 
cannot  at  first  be  determined  with  reagent  papers,  because  the 
sulphuric  acid  decomposes  the  organic  salts,  neutral  sulphates 
being  formed,  and  a  quantity  of  organic  acid  equivalent  to 
the  sulphuric  acid  is  liberated.  For  this  reason  the  content 
of  metal  in  the  bath  declines,  though  the  presence  of  sulphuric 
acid  cannot  be  established,  because  the  sulphuric  acid  formed 
by  electrolysis  is  not  consumed  for  the  solution  of  nickel  on 
the  anodes,  but  for  the  decomposition  of  the  organic  salts. 

Now  let  us  suppose  the  reverse,  namely,  that  in  a  nickel 
bath  prepared  with  the  addition  of  one  of  the  above-mentioned 
-acids,  free  ammonia  appears  in  consequence  of  the  sole  use  of 
cast  anodes,  and  of  the  decomposition  of  ammonium  sulphate 
by  a  strong  current.  This  phenomenon  cannot  at  once  be 
recognized,  because  the  ammonia  is  first  fixed  by  the  free 
-acid,  and  the  bath  becomes  neutral  or  alkaline  only  when  all 
the  free  acid  which  was  present  has  been  consumed  for  fixing 
the  ammonia  formed.  With  this  process  there  will  generally 
be  connected  an  increase  in  the  content  of  the  metal,  and  it 
will  be  seen,  without  further  explanation,  that  for  the  accurate 
determination  of  the  processes  and  alterations  in  a  nickel  bath 
when  in  operation,  the  quantitative  determination  of  the  free 
-acids,  and  as  much  as  possible,  that  of  the  content  of  metal,  is 
required. 

Although  it  may  be  said  that  the  busy  electro-plater  will 
frequently  not  feel  inclined  to  familiarize  himself  with  the 
methods  of  testing,  and  seldom  have  the  necessary  time  for 
executing  the  determinations  of  the  content  of  metal,  neverthe- 


318  ELECTRO-DEPOSITION    OF    METALS.. 

less  the  methods  will  here  be  described  with  sufficient  detail, 
so  that  those  who  wish  to  examine  their  baths  in  this  respect 
will  find  the  necessary  instructions.  To  be  sure,  if  the  electro- 
plater  himself  is  not  a  practical  analytical  chemist  he  will  have 
to  be  taught  by  some  one  thoroughly  conversant  with  the  sub- 
ject the  management  of  the  analytical  balance,  how  to  execute 
the  weighings,  etc.  It  is  also  advisable  to  procure  the  stand- 
ard solutions  required  for  volumetric  analysis  from  a  reliable 
chemical  laboratory,  in  order  to  avoid  the  possibility  of  arriv- 
ing at  incorrect  results  by  the  use  of  inaccurately  prepared 
standard  solutions.  For  this  reason  directions  for  the  prepa- 
ration of  standard  solutions  are  omitted,  and  the  methods  of 
examination  in  use  for  our  purposes  will  now  be  given. 

The  examinations  may  be  made  by  gravimetric  analysis- 
Analysis  by  weight),  volumetric  analysis  (analysis  by  meas- 
ure), and  by  electrolytic  analysis.  The  first  method  is  based 
chiefly  upon  the  precipitation  in  an  insoluble  form  of  the  con- 
stituent to  be  determined,  and  filtering,  washing,  drying,  and 
weighing  the  precipitate.  This  method  requires  considerable 
knowledge  of  chemistry  and  analytical  skill,  and  should  only 
be  resorted  to  by  those  not  versed  in  analysis  when  other 
more  practical  methods  for  the  determination  of  the  contents-, 
such  as  volumetric  and  electrolytic  methods,  are  not  known. 

Volumetric  analysis  is  based  upon  a  very  different  principle 
from  that  of  gravimetric  analysis.  The  constituent  to  be  ascer- 
tained is  quantitatively  determined  by  means  of  a,  standard 
solution,  enough  of  which  is  used  until  the  final  reaction  shows 
that  a  sufficient  quantity  has  been  added.  From  the  known 
content  of.  the  standard  solution  the  constituent  to  be  deter- 
mined is  then  calculated.  This  may  be  explained  by  an 
example.  For  instance,  the  content  of  sulphuric  acid  in  a 
fluid  is  to  be  determined.  Measure  the  quantity  of  fluid  by 
means  of  a  pipette  which  up  to  a  mark  holds  exactly  10  cubic 
centimeters.  Allow  the  fluid  to  run  into  a  clean  beaker, 
dilute  with  about  30  cubic  centimeters  of  water,  and  heat  to 
about  122°  F.  Now,  while  constantly  stirring  the  fluid  in. 


DEPOSITION    OF    NICKEL    AND    COBALT.  319' 

the  beaker  with  a  glass  rod,  add  standard  soda  solution  from- 
a  glass  burette  provided  with  a  glass  cork  and  divided  into -iV 
cubic  centimeters  until  a  piece  of  congo  paper  when  touched 
with  the  glass  rod  is  no  longer  colored  blue.  The  addition  of 
the  standard  soda  solution  must,  of  course,  be  effected  with 
great  care.  So^  long  as  the  congo  paper  shows  a  vivid  blue 
color,  a  larger  quantity  may  at  one  time  be  added,  but  when 
the  colorization  becomes  less  vivid,  the  solution  is  added  drop 
by  drop  so  as  to  be  sure  that  the  last  drop  is  just  sufficient  to 
prevent  the  blue  coloration  which  was  still  perceptible  after 
the  addition  of  the  previous  drop.  The  drop-test  must,  or 
course,  be  made  upon  a  dry  portion  of  the  congo  paper,  which 
has  not  been  previously  moistened.  When  no  blue  coloration 
appears  after  the  last  drop  has  been  added,  it  is  a  proof  that 
all  the  sulphuric  acid  present  has  been  neutralized  by  the 
standard  soda  solution.  The  number  and  fractions  of  cubic 
centimeters  consumed  are  then  read  off  on  the  burette,  and 
the  quantity  of  sulphuric  acid  present  is  calculated  as  fol- 
lows :  1  cubic  centimeter  of  standard  soda  solution  neutralizes 
0.049  gramme  of  sulphuric  acid  (H2S04),  and  hence  the 
quantity  of  sulphuric  acid  is  obtained  by  multiplying  the 
number  of  cubic  centimeters  of  standard  soda  solution  by 
0.049.  Now,  since  10  cubic  centimeters  were  measured  off 
by  the  pipette  and  titrated,  the  number  found  is  multiplied 
by  100,  which  gives  the  content  of  sulphuric  acid  in  1  liter  of 
,the  fluid. 

If,  for  instance,  for  the  neutralization  of  10  cubic  centi- 
meters of  the  fluid  containing  sulphuric  acid,  5.4  cubic  centi- 
meters of  standard  soda  solution  were  required,  then  the 
content  of  sulphuric  acid  amounts  to  5.4x0.049=0.2646- 
gramme,  or  in  1  liter  to  0.2646  X  100  =  26.46  grammes. 

The  electrolytic  method  of  analysis  is  available  only  for  the- 
determination  of  such  metals  as  can  be  completely  separated 
in  a  cohere'nt  form  from  their  solutions  by  the  current.  It  is 
based  upon  the  fact  that  the  metallic  solution  contained  in  a 
platinum  dish  is  decomposed  by  the  current,  and  the  metal 


-320 


ELECTRO-DEPOSITION    OF    METALS. 


precipitated  upon  the  platinum  dish.  After  washing  and 
drying,  the  dish  is  weighed  and  the  weight  of  the  precipitated 
metal  is  obtained  by  deducting  the  weight  of  the  platinum 
dish  without  precipitate,  which,  of  course,  has  been  ascertained 
before  making  the  experiment. 

The  apparatus  generally  used  for  electrolytic  analysis  is 
shown  in  Fig.  122.  The  platinum  dish,  holding  about  J  liter, 
rests  upon  a  metal  ring  which  is  secured  to  the  rod  of  the 
stand,  and  is  in  contact  with  the  negative  pole  of  the  source 

FIG.  122. 


of  current.  Into  the  dish,  at  a  distance  of  1  or  2  centimeters 
from  the  bottom,  dips  a  round  platinum  disk  bent  like  the 
bottom,  or  a  spiral  of  platinum  wire,  1  millimeter  thick,  which 
serves  as  an  anode  and  is  secured  by  platinum  wire  in  a  mov- 
able support  or  holder.  The  latter  is  carefully  insulated  from 
the  rod  of  the  stand  and  connected  with  the  positive  pole  of 
the  source  of  current.  During  electrolysis  the  platinum  dish 
is  covered  with  a  perforated  watch-glass  to  prevent  possible 
loss  by  the  evolution  of  gas. 


DEPOSITION    OF    NICKEL    AND    COBALT.  321 

Since  many  precipitates  have  to  be  washed  without  inter- 
rupting the  current,  it  is  best  to  use  the  washing  contrivance 
-shown  in  the  illustration  to  prevent  the  precipitated  metal 
from  being  redissolved  by  the  electrolyte.  With  the  upper 
clip  closed,  the  shorter  leg  of  the  siphon  is  dipped  into  the 
dish.  The  lower  clip  is  then  closed  and  the  upper  one  opened 
until  the  short  leg  is  filled  with  water.  The  upper  clip  is 
then  closed  and  the  lower  one  opened,  whereby  the  dish  is 
emptied.  The  clip  of  the  longer  leg  of  the  siphon  is  then 
closed,  the  uppermost  clip  opened,  and  the  dish  filled  up  to 
the  rim  with  water.  The  uppermost  clip  is  then  closed,  the 
lower  one  opened,  and  the  dish  emptied  the  second  time,  the 
operation  being  repeated  until  the  precipitate  and  dish  are 
thoroughly  washed. 

Since  for  complete  electrolytic  precipitation  it  is  essential  to 
operate  with  correct  electro-motive  forces,  it  is  advisable  to 
use  an  accurate  ammeter  adjusted  to  0.05  to  2.5  amperes,  as 
well  as  a  voltmeter. 

The  current  for  electrolysis  may  be  supplied  by  cells,  a 
thermo-electric  pile,  a  dynamo,  or  an  accumulator,  but  the 
necessary  regulating  resistances  must  in  every  case  be  provided. 

Let  us  now  return  to  the  examination  of  nickel  baths.  If 
by  qualitative  analysis  the  presence  of  free  sulphuric  acid  in 
the  bath  has  been  established,  it  can  be  at  once  assumed  that 
the  content  of  nickel  has  from  the  first  declined.  Hence  it 
will  scarcely  be  worth  while  to  determine  by  volumetric  analy- 
sis the  quantity  of  free  sulphuric  acid  present,  and  to  calculate 
from  this  the  quantity  of  nickel  carbonate  or  nickel  hydrate 
required  for  neutralization.  It  will  be  only  necessary  to  add 
to  the  bath,  stirring  constantly,  small  portions  of  the  nickel 
salt  rubbed  up  with  water,  until  a  fresh  test  with  congo  paper 
shows  no  blue  coloration.  The  addition  of  a  small  excess  of 
nickel  carbonate  or  mckel  hydrate  is  unobjectionable.  Besides 
neutralizing  the  free  sulphuric  acid,  care  should  at  the  same 
time  be  taken  to  prevent  its  further  formation  by  increasing 
the  number  of  cast-nickel  anodes.  The  case  is  similar  when 
22 


322  ELECTRO-DEPOSITION    OF    METALS. 

a  nickel  bath  prepared  with  organic  salts,  for  instance,  with 
potassium  citrate  or  sodium  citrate,  is  to  be  examined.  Even 
if  it  is  shown  by  the  reaction  that  no  free  sulphuric  acid  is 
present,  the  content  of  nickel,  as  previously  mentioned,  may 
have  decreased,  and  the  content  of  free  organic  acid  increased. 
The  latter  may,  however,  be  neutralized  by  the  addition  of 
nickel  carbonate  or  nickel  hydrate,  and  hence  the  determina- 
tion of  the  content  of  acid  by  volumetric  analysis  is  not 
absolutely  necessary. 

When,  on  the  other  hand,  a  nickel  bath  has  become  alkaline, 
the  determination  of  the  free  alkali  by  volumetric  analysis  will 
be  of  little  value,  and  it  will,  according  to  the  composition  of 
the  bath,  suffice  to  neutralize  it  with  dilute  sulphuric  acid,  or 
acidulate  it  with  an  organic  acid.  Since,  however,  baths  which 
have  become  alkaline  possess  a  higher  content  of  nickel  than 
the  normal  bath,  an  electrolytic  determination  of  the  nickel 
may  be  of  use  in  order  to  calculate  accurately  the  quantity  of 
water  which  has  to  be  added  to  reduce  the  content  of  nickel 
to  the  normal  quantity. 

If  the  bath  has  been  prepared  with  nickel-ammonium  sul- 
phate with  additions  of  ammonium  sulphate,  or  boric  acid,  or 
if  it  contains  only  very  small  quantities  of  organic  acids,  it 
can  be  directly  electrolyzed. 

Bring  by  means  of  the  pipette  exactly  20  cubic  centimeters 
of  the  bath  into  the  platinum  dish,  add  4  grammes  of  ammo- 
nium sulphate  and  35  to  40  cubic  centimeters  of  ammonia  of 
0.96  specific  gravity  and  electrolyze  with  a  current-density  = 
0.6  ampere  until  no  dark  coloration  appears  after  adding  a 
drop  of  ammonium  sulphate  to  a  few  cubic  centimeters  of  the- 
electrolyte.  Rinse  the  dish,  together  with  the  precipitate,  with 
water,  remove  the  water  by  rinsing  with  absolute  alcohol,  rinse- 
the  dish  with  pure  ether  and  dry  at  212°  F.  in  an  air-bath. 
The  weight  of  the  precipitate  of  metallic  nickel  obtained  by 
weighing  the  platinum  dish  gives  the  content  of  nickel  am- 
monium sulphate  in  grammes  per  liter  of  bath  by  multiplying 
by  335.  From  the  increase  in  the  content  of  nickel  ammo- 


DEPOSITION    OF    NICKEL    AND    COBALT.  323 

nium  sulphate  shown  by  the  analysis,  it  can  be  readily  cal- 
culated how  much  water  has  to  be  added  to  the  bath  to  reduce 
it  to  the  original  content. 

If  a  nickel  bath  contains  large  quantities  of  organic  acids, 
precipitate  20  cubic  centimeters  of  the  bath  with  sodium  sul- 
phide solution,  filter  and  wash  the  precipitate,  dissolve  it  in 
nitric  acid,  and  evaporate  the  solution  with  pure  sulphuric 
acid  upon  the  water-bath  to  drive  off  the  nitric  acid.  The 
residue  is  treated  as  above  described. 

2.  DEPOSITION  OF  COBALT. 

Properties  of  cobalt.  Cobalt  (Co  =  58.97  parts  by  weight) 
has  nearly  the  same  color  as  nickel,  with  a  slightly  reddish 
tinge ;  its  specific  gravity  is  8.7.  It  is  exceedingly  hard, 
highly  malleable  and  ductile,  and  capable  of  taking  a  polish. 
It  is  slightly  magnetic,  and  preserves  this  property  even  when 
alloyed  with  mercury.  It  is  rapidly  dissolved  by  nitric  acid, 
and  slowly  by  Dilute  sulphuric  and  hydrochloric  acids. 

For  plating  with  cobalt,  the  baths  given  under  "  Nickeling  " 
may  be  used  by  substituting  for  the  nickel  salt  a  correspond- 
ing quantity  of  cobalt  salt.  By  observing  the  rules  given 
for  nickeling,  the  operation  proceeds  with  ease.  Anodes  of 
metallic  cobalt  are  to  be  used  in  place  of  nickel  anodes. 

Nickel  being  cheaper  and  its  color  somewhat  whiter,  electro- 
plating with  cobalt  is  but  little  practiced.  On  account  of  the 
greater  solubility  of  cobalt  in  dilute  sulphuric  acid,  it  is,  how- 
ever, under  all  circumstances,  to  be  preferred  for  facing  valu- 
able copper  plates  for  printing. 

According  to  the  more  or  less  careful  adjustment  of  such 
plates  in  the  press,  the  facing  in  some  places  is  more  or  less 
attacked,  and  it  may  be  desired  to  remove  the  coating  and 
make  a  fresh  deposit.  For  this  purpose  Gaiffe  has  proposed 
the  use  of  cobalt  in  place  of  nickel,  because  the  former  dis- 
solves slowly  but  completely  in  dilute  sulphuric  acid.  He 
recommends  a  solution  of  1  part  of  chloride  of  cobalt  in  10  of 
water.  The  solution  is  to  be  neutralized  with  aqua  ammonia, 


324  ELECTRO-DEPOSITION    OF    METALS. 

and  the  plates  are  to  be  electro-plated  with  the  use  of  a 
moderate  current. 

Cobalt  precipitated  from  its  chloride  solution,  however,  does 
not  yield  a  hard  coating,  and  hence  the  following  bath  is 
recommended  for  the  purpose :  Double  sulphate  of  cobalt  and 
ammonium  21  ozs.,  crystallized  boric  acid  10J  ozs.,  water  10 
quarts. 

The  bath  is  prepared  in  the  same  manner  as  No.  VII,  given 
under  "  Deposition  of  Nickel."  It  requires  an  electro-motive 
force  of  2.5  to  2.75  volts  ;  current-density,  0.4  ampere. 

Prof.  Sylvanus  Thompson's  solutions  for  the  electro-deposi- 
tion of  cobalt,  patented  by  him  in  1887,  yield  very  satisfactory 
results  : 

I.  Double  sulphate  of  cobalt  and  ammonium  16  ozs.,  mag- 
nesium sulphate  8  ozs.,  ammonium  sulphate  8  ozs.,  citric  acid 
1  oz.,  water  1^  gallons. 

II.  Cobalt    sulphate   8    ozs.,   magnesium   sulphate   4    ozs., 
ammonium   sulphate  4   ozs.,  water  1-J-  gallon  j,     It  is  best  to 
use  the  solutions  warm,  at  about  95°  F. 

To  determine  whether  copper,  and  how  much  of  it,  is  dis- 
solved in  stripping  the  cobalt  deposit  from  cobalted  copper 
plates,  a  copper  plate  with  a  surface  of  7|  square  inches  was 
coated  with  7.71  grains  of  cobalt  and  placed  in  dilute  sul- 
phuric acid  (1  part  acid  of  66°  Be.  to  12.5  parts  of  water). 
After  the  acid  had  acted  for  14  hours,  the  cobalt  deposit  was 
partially  dissolved,  and  had  partially  collected  in  laminae 
upon  the  bottom  of  the  vessel,  the  copper  plate  being  entirely 
freed.  On  weighing  the  copper  plate  it  was  shown  that  it 
had  lost  about  0.0063  per  cent.,  this  loss  being  apparently 
chiefly  from  the  back  of  the  plate,  the  engraved  side  exhibit- 
ing no  trace  of  corrosion.  The  experiment  proved  that  there 
is  no  danger  of  destroying  the  copper  plate  by  stripping  the 
cobalt  deposit  with  dilute  sulphuric  acid,  provided  the  opera- 
tion is  executed  with  due  care  and  attention. 

Warren  has  described  a  cobalt  solution  which  can  be  decom- 
posed in  a  single-cell  apparatus,  and  for  this  reason  would  seem 


DEPOSITION    OF    NICKEL    AND    COBALT.  325 

suitable  for  electro-plating  small  articles  in  quantities.  For 
the  preparation  of  this  bath,  dissolve  3J  ounces  of  chloride  of 
cobalt  in  as  little  water  as  possible,  and  compound  the  solution 
with  concentrated  solution  of  Rochelle  salt  until  the  volumi- 
nous precipitate  at  first  formed  is  almost  entirely  redissolved, 
and  then  filter.  Bring  the  bath  into  a  vessel  and  place  the 
latter  in  a  clay  cup  filled  with  concentrated  solution  of  chlo- 
ride of  ammonium  or  of  common  salt,  and  containing  a  zinc 
cylinder.  Connect  the  objects  to  be  plated  to  the  zinc  by  a 
copper  wire,  and  allow  them  to  dip  in  the  cobalt  solution. 
With  a  closed  circuit  the  objects  become  gradually  coated 
with  a  lustrous  cobalt  deposit  which,  after  2  hours,  is  suffi- 
ciently heavy  to  bear  vigorous  polishing  with  the  bob.  Coat- 
ing zinc  in  the  same  manner  was  not  successful. 


CHAPTER  VII. 

DEPOSITION  OF  COPPER,  BRASS  AND  BRONZE. 
1.  DEPOSITION  OF  COPPER. 

Properties  of  copper.  Copper  (Cu  =  63.57  parts  by  weight) 
has  a  characteristic  red  color,  and  possesses  strong  luster.  It 
is  very  tenacious,  may  be  rolled  to  thin  laminae,  and  readily 
drawn  into  fine  wire.  The  specific  gravity  of  wrought  copper 
is  8.95,  and  of  cast,  8.92.  Copper  fuses  more  readily  than 
gold,  but  with  greater  difficulty  than  silver. 

In  a  humid  atmosphere  containing  carbonic  acid,  copper 
becomes  gradually  coated  with  a  green  deposit  of  basic  car- 
bonate. When  slightly  heated  it  acquires  a  red  coating  of 
cuprous  oxide,  and  when  strongly  heated  a  black  coating  of 
cupric  oxide  with  some  cuprous  oxide.  Copper  is  most  read- 
ily attacked  by  nitric  acid,  but  is  slowly  dissolved  when  im- 
mersed in  heated  hydrochloric  or  sulphuric  acid.  With 
exclusion  of  the  air,  it  is  not  dissolved  by  dilute  sulphuric  or 
hydrochloric  acid,  and  but  slightly  with  admission  of  the  air. 
Liquid  ammonia  causes  a  rapid  oxidation  of  copper  in  the 
air  and  the  formation  of  a  blue  solution.  An  excess  of  potas- 
sium cyanide  dissolves  copper.  Sulphuretted  hydrogen  black- 
ens bright  copper. 

Copper  baths.  The  composition  of  these  baths  depends  on 
the  purpose  they  are  to  serve,  and  below  are  mentioned  the 
most  approved  baths,  with  the  exception  of  the  acid  copper 
bath  used  for  plastic  deposits  of  copper,  which  will  be  dis- 
cussed later  on  under  "  Copper  Galvanoplasty." 

In  most  cases  the  more  electro-positive  metals,  zinc,  iron, 
tin,  etc.,  are  to  be  coppered  either  as  preparation  for  the  suc- 
ceeding processes  of  nickeling,  silvering,  or  gilding,  or  to  pro- 

(326) 


DEPOSITION    OF    COPPER,  BRASS    AND    BRONZE.  327 

tect  them  against  oxidation,  or  for  the  purpose  of  decoration. 
The  above-mentioned  electro-positive  metals,  however,  decom- 
pose acid  copper  solutions  and  separate  from  them  pulverulent 
•copper,  while  an  equivalent  portion  of  zinc,  iron,  tin,  etc.,  is 
dissolved.  For  this  reason,  such  solutions  cannot  be  used  for 
coating  these  metals,  and  alkaline  copper  baths  are  exclusively 
employed,  which  may  be  arranged  under  two  groups — those 
containing  potassium  cyanide,  and  those  without  it. 

Copper  cyanide  baths  are  prepared  by  dissolving  cupric  salts, 
for  instance,  cupric  acetate  (verdigris),  cupric  sulphate  (blue 
vitriol),  or  cuprous  compounds,  such  as  cuprous  oxide,  in 
potassium  cyanide,  the  salt^  being  thereby  converted  into 
potassium-copper  cyanide,  which  is  the  effective  constituent 
of  all  copper  cyanide  baths. 

By  compounding  a  solution  of  a  cupric  salt  with  potassium 
•cyanide,  cupric  cyanide  is  formed,  which  is  very  unstable, 
rapidly  changing  by  exposure  into  cupro-cupric  cyanide  and 
cyanogen  gas.  To  avoid  this  loss  of  cyanogen,  sulphites  are 
added,  which,  according  to  one  view,  effect  a  reduction  of  the 
^cupric  salts  to  cuprous  salts,  which  dissolve  in  potassium 
cyanide  without  cyanogen  being  liberated,  while,  according 
to  another,  hydrocyanic  acid  is  produced  from  cyanogen  gas 
and  sodium  sulphite,  water  being  decomposed,  and  forms 
with  the  sodium  carbonate  present,  sodium  cyanide,  the  latter 
becoming  again  active  in  converting  the  cupro-cupric  cyanide 
into  the  soluble  double  salt.  It  is  possible  that  both  the 
reactions  mentioned  above  partly  appear  together. 

By  using  from  the  start  cuprous  oxide,  the  latter  can  with- 
out loss  of  cyanogen  be  converted  into  potassium-copper 
-cyanide. 

In  accordance  with  this,  there  will  be  given  in  the  formulas 
for  the  preparation  of  potassium-copper  cyanide  baths  in 
which  cupric  salts  are  used,  larger  or  smaller  additions  of 
bisulphite  of  soda  and  alkaline  carbonates,  the  former  serving 
the  purpose  of  decreasing  the  loss  of  cyanogen,  and  the  latter 
<being  intended  to  fix  any  free  acid  formed. 


328  ELECTRO-DEPOSITION    OF    METALS. 

Stockmeier  was  the  first  to  take  the  trouble  of  calculating 
the  combinations  formed  after  the  conversion  of  the  separate 
constituents  of  the  copper  baths,  and  Jordis  has  adopted  the 
same  course,  in  order  to  obtain  a  standard  formula.  Both 
these  authors  recommend  not  to  produce  the  copper  combina- 
tion actually  subjected  to  electrolysis  in  the  bath  by  repeated 
conversions  of  salts,  but  to  prepare  this  combination  by  itself, 
and  to  dissolve  it  direct  in  water  in  order  to  obtain  the  finished 
copper  bath.  It  has  been  shown  in  practice  that  this  method 
is  quite  practicable  provided  certain  points  are  taken  into  con- 
sideration. However,  the  rational  composition  of  a  bath  with 
potassium  cyanide,  which  has  been  produced  by  conversion- 
from  the  salts,  cannot  be  judged  according  to  whether  the  sep- 
arate salts  were  present  in  stoichoimetrical  proportions  for  the 
smooth  conversion  into  new  combinations  without  receiving  in 
the  bath  an  excess  from  one  or  the  other  substance.  In  prac- 
tice it  has  long  been  known  that  an  excess  of  sodium  bisulphite 
has  a  very  beneficial  effect  upon  the  separation  of  a  lustrous- 
copper,  and  prevents  it  from  rapidly  turning  into  a  dull  earthy 
gray,  this  effect  being  very  likely  due  to  the  prussic  acid  lib- 
erated by  the  sulphurous  acid.  This  one  example  may  prove- 
that  standard  formulas  erected  upon  theoretical  maxims  should 
be  accepted  with  due  caution  by  the  practical  electro-plater,, 
and  that,  under  certain  conditions,  additions  will  have  to  be 
made  to  baths  prepared  according  to  such  standard  formulas- 
if  the  result  is  to  be  as  good  as  that  from  baths  prepared 
according  to  older  formulas. 

Hossauer  prepares  a  copper  bath  by  dissolving  '3J  ozs.  of 
copper  cyanide  in  a  solution  of  17J  ozs.  of  70  per  cent,  potas- 
sium cyanide  in  3  quarts  of  water,  boiling,  filtering  and  dilu- 
ting with  7  quarts  of  water,  to  a  10-quart  bath.  This  bath 
works  very  well  when  heated  to  between  113°  and  122°  F.,. 
but  when  used  cold  requires  a  very  strong  current. 

Roseleur  has  recommended  the  use  of  copper  acetate  (ver- 
digris) for  copper  baths,  and  suitable  compositions,  slightly 
modified,  are  as  follows  : 


DEPOSITION    OF    COPPER,  BRASS    AND    BRONZE.  329" 

Copper  baths  for  iron  and  steel  articles. — I.  To  be  used  at  the 
ordinary  temperature.  Water  10  quarts,  bisulphite  of  soda  in 
powder  7  ozs.,  crystallized  carbonate  of  soda  14  ozs.,  neutral 
copper  acetate  7  ozs.,  75-per  cent,  potassium  cyanide  7  ozs.,. 
ammonia  4.4  ozs. 

II.  For  hot  coppering  (at  between  14-0°  and  158°  F.).  Water 
10  quarts,  bisulphite  of  soda  in  powder  2}  ozs.,  crystallized 
carbonate  of  soda  7  ozs.,  neutral  copper  acetate  7  ozs.,  75  per 
cent,  cyanide  of  potassium  6f  ozs.,  ammonia  4  ozs. 

The  baths  are  best  prepared  as  follows  :  Dissolve  the  bisul- 
phite and  carbonate  of  soda  in  one-half  of  the  water,  the  potas- 
sium cyanide  in  the  other  half,  and  mix  the  copper  salt  with 
the  ammonia  ;  then  pour  the  blue  ammoniacal  copper  solution 
into  the  solution  of  the  soda  salts,  and  finally  add  the  potas- 
sium cyanide  solution ;  the  bath  will  then  be  clear  and  color- 
less. Boiling,  though  not  absolutely  necessary,  is  of  advan- 
tage, after  which  the  solution  is  to  be  filtered. 

According  to  thorough  investigations  made,  the  excess  of 
carbonate  of  soda  in  formula  I  serves  no  special  purpose,  but 
on  the  contrary,  in  many  cases,  is  directly  detrimental ; 
neither  is  the  use  of  ammonia  of  any  special  advantage,  and 
it  may  just  as  well,  or  rather  better,  be  omitted.  Further, 
the  use  of  separate  baths  for  cold  and  warm  coppering  is  at 
least  questionable.  It  is  believed  that  a  single  bath  suffices 
for  both  cases,  heating  having  been  found  of  special  advantage 
only  for  rapid  and  thick  coppering,  or  for  obtaining  particu- 
lar shades  which  are  produced  with  difficulty  in  the  cold 
bath,  but  without  trouble  in  the  heated  bath. 

It  should  be  borne  in  mind  that  potassium  cyanide  solu- 
tions are  still  more  rapidly  decomposed  when  heated  than 
when  used  cold,  and  consequently  the  consumption  of  potas- 
sium cyanide  in  heated  baths  is  considerably  greater  than  in 
cold  baths.  Recourse  to  heating  should,  therefore,  only  be 
had  when  the  intended  result  cannot  by  any  other  means  be 
obtained. 

The  following  formula  may   be    highly   recommended,  a. 


330  ELECTRO-DEPOSITION    OF    METALS. 

copper  bath  composed  according  to  it  always  yielding  good 
and  sure  results. 

III.  Water  10  quarts,  crystallized  carbonate  of  soda  8J  ozs., 
-crystallized  bisulphite  of  soda  7  ozs.,  neutral  copper  acetate 
7  ozs.,  98  or  99  per  cent,  potassium  cyanide  8J  ozs. 

Electro-motive  force  at  10  cm.  electrode-distance,  3  volts. 

Current-density,  0.35  ampere. 

The  bath  is  prepared  as  follows :  Dissolve  in  7  quarts  of 
warm  water  the  carbonate  of  soda,  gradually  add  the  bisul- 
phite of  soda  to  prevent  violent  effervescence,  and  then  add, 
with  vigorous  stirring,  the  copper  acetate  in  small  portions. 
Dissolve  the  potassium  cyanide  in  3  quarts  of  cold  water,  and 
mix  both  solutions  when  the  first  is  cold.  By  thorough  stir- 
ring with  a  clean  wooden  stick,  a  clear  solution  is  quickly 
obtained,  which  is  allowed  to  settle  and  siphoned  off  clear. 
If  after  the  addition  of  the  potassium  cyanide  the  bath  should 
not  become  colorless,  or  at  least  wine-yellow,  add  a  small 
-quantity  more  of  potassium  cyanide. 

When  conversion  is  complete,  the  bath  contains  potassium- 
copper  cyanide,  potassium  acetate,  sodium  acetate,  sodium 
sulphate,  and  potassium  cyanide  in  excess  in  addition  to 
sodium  bisulphita 

For  certain  purposes,  for  instance,  for  the  production  of  a 
very  close,  thick  deposit,  as  required  for  cast-iron  door  knobs, 
-etc.,  it  is  advisable  to  double  the  content  of  metal.  For  the 
preparation  of  such  a  copper  bath  it  is  only  necessary  to  dis- 
solve double  the  quantities  of  the  salts  given  in  formula  III 
in  10  quarts  of  water. 

Stockmeier  recommends  the  following  copper  bath : 

Ilia.  Water  10  quarts,  neutral  bisulphite  of  soda  8J  ozs., 
'98-  or  99-percent,  potassium  cyanide  7  ozs.,  crystallized  car- 
bonate of  soda  6  ozs.,  crystallized  copper  acetate  7  ozs. 

Dissolve  the  first  mentioned  three  salts  together  in  half  the 
•quantity  of  the  water,  and  the  acetate  of  copper  in  the  other 
'half,  and  pour  the  last  solution  into  the  first,  stirring  con- 
stantly. It  is  recommended  to  add  to  this  bath  77  to  123 
grains  *of  bisulphite  ^of  soda  per  quart. 


DEPOSITION    OF    COPPER,  BRASS    AND    BRONZE.  331 

In  preparing  copper  baths,  the  copper  acetate  prescribed  in 
the  preceding  formulae  may  be  replaced  by  the  carbonate  or 
sulphate,  the  substitution  of  the  latter,  after  its  previous  con- 
version into  carbonate,  being  of  special  advantage  in  order 
not  to  thicken  the  bath  by  the  potassium  sulphate  formed  by 
reciprocal  decomposition.  The  following  formula  is  especially 
suitable  for  the  use  of  sulphate  of  copper  (blue  vitriol): 

IV.  Blue  vitriol 10J  ozs. 

Crystallized  carbonate  of  soda          .         .     10J  ozs. 

Water .10  quarts. 

Pulverized  bisulphite  of  soda  ...  7  ozs. 
Crystallized  carbonate  of  soda.  .  .  8J  ozs. 
98  to  99  per  cent,  potassium  cyanide  .  8J  ozs. 

Electro-motive  force  at  10  cm.  electrode-distance,  about  3 
volts. 

Current-density,  0.35  ampere. 

First  dissolve  the  10  J  ozs.  of  blue  vitriol  and  the  10 J  ozs. 
of  crystallized  carbonate  of  soda,  each  by  itself,  in  hot  water, 
and  mix  the  two  solutions.  Allow  the  precipitate  of  carbonate 
of  copper  to  settle,  and  pour  off  the  supernatant  clear  fluid. 
Then  pour  upon  the  precipitate  5  quarts  of  water,  add  the 
bisulphite  of  soda,  next  the  carbonate  of  soda,  and  mix  this 
solution  with  the  solution  of  the  potassium  cyanide  in  5 
quarts  of  water.  The  fluid  rapidly  becomes  clear  and  color- 
less, when  it  is  boiled  and  filtered. 

V.  Water  15  quarts,  cupron  (cuprous  oxide)  3J  ozs.,  99  per 
«jent.  potassium  cyanide  10 J  ozs.,  bisulphite  of  soda  10 J  ozs. 

Electro-motive  force  at  10  cm.  electrode-distance,  2.8  volts. 

Current-density,  0.3  ampere. 

For  the  preparation  of  the  bath,  dissolve  the  potassium 
•cyanide  in  about  3  quarts  of  the  water  (cold),  stir  in  gradually 
the  cupron,  then  add  the  solution  of  the  bisulphite  of  soda  in 
3  quarts  of  the  water,  and  with  the  remaining  9  quarts  of 
water  make  up  the  bath  to  15  quarts. 

As  previously  mentioned,  an  addition  of  sulphites  to  the 


332  ELECTRO-DEPOSITION    OF    METALS. 

cuprous  oxide  solution  is  not  required  since  no  cyanogen* 
escSpes.  However,  in  dissolving  cuprous  oxide  in  potassium 
cyanide  there  is  formed,  in  addition  to  potassium-copper  cya- 
nide, potassium  hydroxide  (caustic  potash)  the  presence  of 
which  in  the  bath  is  for  various  reasons  not  desirable.  A 
sufficient  quantity  of  bisulphite  of  soda  to  convert  the  caustic 
potash  into  neutral  potassium  sulphite  is  therefore  added, 
while  the  corresponding  portion  of  bisulphite  is  converted 
into  neutral  sodium  bisulphite.  A  sufficient  excess  of  bisul- 
phite of  soda  for  the  exertion  of  the  above-mentioned  favor- 
able effects  upon  the  coppering  process  remains  behind. 

Dr.  Langbein  has  introduced  in  the  copper-plating  industry 
the  cupro-cupric  sulphite.  It  dissolves  in  potassium  cyanide 
without  noticeable  formation  of  cyanogen,  since  it  contains 
more  than  the  sufficient  quantity  of  sulphurous  acid  required 
for  the  reduction  of  the  portion  of  cupric  oxide  present.  Suit- 
able formulas  for  copper  baths  with  cupro-cupric  sulphite  are  : 

VI.  Water  10  quarts,  99  per  cent,  potassium  cyanide  8J 
ozs.,  ammonium  soda  If  ozs.,  cupro-cupric  sulphite  4J  ozs.,  or, 

Via.  Water  10  quarts,  60  per  cent,  potassium  cyanide  14 
ozs.,  cupro-cupric  sulphite  4J  ozs. 

Dissolve  the  salts  in  the  order  given,  stirring  constantly, 
and  then  add  the  remaining  5  quarts  of  water. 

The  deposits  obtained  in  these  baths  are  of  a  beautiful 
warm  color,  very  adherent  and  dense. 

Pfanhauser  recommends  the  following  bath,  in  which 
separately  prepared  crystallized  potassium -copper  cyanide,  in 
addition  to  suitable  conducting  salts,  which  are  wanting  in 
Hossauer's  formula,  is  used  : 

VII.  Water  10   quarts,  ammonia-soda  3J  ozs.,  anhydrous 
sodium  sulphite  7  ozs.,  crystallized  potassium-copper  cyanide 
10J  ozs.,  potassium  cyanide  0.35  ozs. 

For  the  preparation  of  the  bath  the  salts  are  to  be  dissolved 
in  a  suitable  quantity  of  water,  stirring  constantly. 

Electro-motive  force  at  an  electrode  distance  of  15  cm.,  2.7 
volts  for  iron,  3.2  volts  for  zinc.  Current-density  0.3  ampere. 


DEPOSITION    OF    COPPER,  BRASS    AND    BRONZE.  333 

For  small  zinc  objects  which  are  to  be  coppered  in  a  basket, 
baths  III,  IV,  and  V.  may  be  used,  or  those  up  to  and  in- 
cluding VII,  which  are  to  be  heated  and  compounded  with  a 
small  additional  quantity  of  potassium  cyanide.  For  the 
same  purpose,  Roseleur  recommends  the  following  bath: 

VIII.  Water  10  quarts,  neutral  crystallized  sodium  sulphite 
1}  ozs.,  neutral  copper  acetate  8  ozs.,  75-per  cent,  potassium 
cyanide  12J-  ozs,,  ammonia  3  ozs. 

T-he  bath  is  prepared  in  the  same  manner  as  the  baths  given 
under  formulas  I  to  III. 

Prepared  coppering  salts.  Combinations  under  various  names 
(Schering :  triple  metal  salts ;  Langbein  Co.  :  double  metal 
salts)  are  now  brought  into  commerce,  and  are  quite  conven- 
ient for  the  preparation  of  copper  baths  (and  brass  baths)  in 
so  far  that  only  one  weighing  of  the  substance  is  required. 

As  regards  their  composition  these  preparations^  are  com- 
binations of  potassium-copper  cyanide  (relatively  potassium- 
zinc  cyanide)  with  alkaline  sulphites,  such  as,  for  instance,  are 
formed  by  dissolving  cupro-cupric  sulphite  in  potassium  cya- 
nide and  subsequent  evaporation  to  dryness.  As  the  copper 
content  in  Langbein  Go's,  double  copper  salt  amounts  to  from 
20  to  21  per  cent.,  copper  baths  with  any  desired  content  of 
metal  can  in  a  very  simple  manner  be  prepared.  Thus,  for 
instance,  a  copper  bath  with  92.59  grains  of  copper  per  quart 
is  obtained  by  dissolving  6.6  Ibs.  of  double  copper  salt  in  100 
quarts  of  water;  and' a  copper  bath  with  138.88  grains  of  cop- 
per per  quart,  by  dissolving  9.9  Ibs.  of  double  copper  salt 
in  100  quarts  of  water.  It  may  be  added  that  there  is  very 
seldom  occasion  to  exceed  138.88  grains  of  copper  per  liter. 

As  these  preparations  can  contain  but  a  small  content  of  free 
.potassium  cyanide  to  prevent  them  from  absorbing  moisture 
when  stored,  it  is  advisable  to  dissolve  in  the  baths  prepared 
from  them  46  to  78  grains  of  99-per  cent,  potassium  cyanide. 
It  has  also  proved  of  advantage  to  add  certain  conducting 
salts,  for  instance,  neutral  sodium  sulphite,  in  order  to  effect 
.a  better  anodal  solution  of  the  copper. 


334  ELECTRO-DEPOSITION    OF    METALS. 

A  copper  salt  brought  into  commerce  by  the  Hanson  &  Van« 
Winkle  Co.  of  Newark,  N.  J.,  under  the  name  of  ruby  oxide^ 
may  to  advantage  be  used  in  making  copper  solutions,  it 
being  claimed  to  give  a  much  deeper  red  deposit  than  is 
possible  to  obtain  with  a  carbonate  solution. 

Copper  baths  without  potassium  cyanide.  Of  the  many  direc- 
tions for  the  preparation  of  these  baths,  only  a  few  need  here 
be  mentioned. 

For  coppering  zinc  objects,  Roseleur  recommends  the  follow- 
ing bath : 

IX.  Water    10    quarts,    tartar,    free   from    lime,    6.7    ozs., 
crystallized  carbonate  of  soda  15  ozs.,  blue  vitriol  6.7  ozs., 
caustic  soda  lye  of  16°  Be.,  }  Ib. 

To  prepare  this  bath,  dissolve  the  tartar  and  the  crystal- 
lized carbonate  of  soda  in  f  of  the  water,  and  the  blue  vitriol 
in  the  remaining  J,  and  mix  both  solutions.  Filter  off  the 
precipitate,  dissolve  it  in  the  caustic  soda  lye,  and  add  this 
solution  to  the  other. 

This  bath  works  very  well,  and  may  be  recommended  to 
electro-platers  who  copper  zinc  exclusively  ;  though  even  for 
this  purpose  the  baths  prepared  according  to  III,  IV  and  V 
answer  equally  well. 

Weill  obtains  a  deposit  of  copper  in  a  bath  consisting  of  a 
solution  of  blue  vitriol  in  an  alkaline  solution  of  tartrate  ot 
potassium  or  sodium.  Such  a  bath  is  composed  as  follows : 

X.  Water  10  quarts,  potassium  sodium  tartrate  (Rochelle 
salt)  53  ozs.,  blue  vitriol  10 J  ozs.,  60  per  cent,  caustic  soda 
28  ozs. 

The  chief  purpose  of  the  large  content  of  caustic  soda  is  to 
keep  the  tartrate  of  copper,  which  is  almost  insoluble  in  water, 
in  solution.  According  to  Weill,  the  coppering  may  be  exe- 
cuted in  three  different  ways,  as  follows: 

The  iron  articles  tied  to  zinc  wires,  or  in  contact  with  zinc 
strips,  are  brought  into  the  bath  ;  the  coppering  thus  taking 
place  by  contact.  Or,  porous  clay  cups  are  placed  in  the 
bath  containing  the  articles ;  these  clay  cups  are  filled  with 


DEPOSITION    OF    COPPER,  BRASS    AND    BRONZE.  335- 

soda  lye  in  which  zinc  plates  connected  with  the  object-rods 
are  allowed  to  dip,  the  arrangement  in  this  case  forming  a 
cell  with  which,  by  the  solution  of  the  zinc  in  the  soda  lye,  a 
current  is  produced,  which  affects  the  decomposition  of  the 
copper  solution  and  the  deposition.  When  saturated  with 
zinc  the  soda  lye  becomes  ineffective,  and,  according  to  Weill, 
it  may  be  regenerated  by  the  addition  of  sodium  sulphite, 
which  separates  the  dissolved  zinc  as  zinc  sulphide.  The  third 
method  of  coppering  consists  in  the  use  of  the  current  of  a  bat- 
tery or  of  a  dynamo  machine,  in  which  case  copper  anodes 
have,  of  course,  to  be  employed.  According  to  the  method 
used,  coppering  is  effected  in  a  shorter  or  longer  time.  In 
contact-coppering  at  least  six  hours  were  required  for  the  pro- 
duction of  a  tolerably  heavy  deposit,  and  with  the  use  of  a 
current  generated  by  an  external  source,  no  other  advantage 
of  this  bath  over  potassium-copper  cyanide  baths  could  be 
noticed  than  that  being  free  from  potassium  cyanide,  it  is  not 
poisonous;  However,  the  danger  in  the  use  of  copper  cyanide 
baths  is  generally  overestimated  by  the  layman,  there  being 
actually  none,  if  proper  care  be  observed. 

Another  copper  bath,  recommended  by  Walenn,  consists  of 
a  solution  of  equal  parts  of  neutral  tartrate  of  ammonia  and 
potassium  cyanide,  in  which  3  to  5  per  cent,  of  copper  (in  the 
form  of  blue  vitriol  or  moist  cupric  hydrate)  is  dissolved.  The 
bath  is  to  be  heated  to  about  140°  F. 

Gauduin's  copper  bath  consists  of  a  solution  of  oxalate  of 
copper  with  oxalate  of  ammonia  and  free  oxalic  acid.  Fon- 
taine asserts  that  the  bath  works  well  when  heated  to  between 
140°  and  150°  F. 

Tanks  for  potassium-copper  cyanide  baths.  Copper  baths  con- 
taining cyanide  cannot  be  brought  into  pitched  tanks,  tanks  of 
stoneware  or  enameled  iron  being  used  for  smaller  baths,  and 
for  larger  ones,  basins  of  brick  set  in  cement,  or  iron  reservoirs 
lined  with  cement.  Wooden  tanks  lined  with  celluloid  are 
also  useful.  For  large  baths  containing  potassium  cyanide 
wooden  tanks  lined  with  lead  can  be  used  without  disadvan- 


'-336  ELECTRO-DEPOSITION    OF    METALS. 

tage,  since  a  slight  coating  of  cyanide  of  lead  which  may  be 
formed  upon  the  lead  is  insoluble  in  potassium  cyanide,  and 

-even  if  a  small  quantity  of  cyanide  of  lead  would  be  dissolved 
in  the  bath  by  the  presence  of  organic  acids,  a  separation  of 
lead  besides  copper  upon  the  cathodes  does  not  take  place. 

Copper  anodes.  For  this  purpose  it  is  best  to  use  annealed 
sheets  of  pure  copper  about  0.11  to  0.19  inch  thick.  They 

•should  first  be  for  some  time  pickled  in  dilute  sulphuric  acid, 
and  then  scratch-brushed,  in  order  to  give  them  a  pure  metal- 
lic surface. 

The  anode-surface  should  be  as  large  as  possible,  at  least  as 
large  as  the  object-surface  suspended  in  the  bath. 

In  all  baths  containing  cyanide  the  anodes  become  in  a 

•  comparatively  short  time  coated  with  a  greenish  slime  which 
consists  of  basic  cuprous  cyanide,  and  is  mostly  soluble  in 
excess  of  potassium  cyanide.  When  a  very  thick  formation 
of  such  slime  takes  place,  potassium  cyanide  is  wanting  and 
has  to  be  added. 

In  addition  to  this  coat  of  cuprous  c}ranide,  there  may  also 
be  formed  upon  the  anode  a  brown  film  of  paracyanide  which 
adheres  very  tenaciously  and  cannot  be  removed  with  potas- 
sium cyanide,  but  has  to  be  taken  off  by  scratch-brushing  or 
scouring  with  pumice.  When  coppering  with  small  anode- 
surfaces,  and  potassium  cyanide  is  at  the  same  time  wanting, 
the  coat  may  become  so  thick  that  no  current  passes  into  the 

•bath,  and  consequently  no  deposit  is  formed.  This  feature 
may  even  appear  when  the  bath  contains  a  sufficient  excess 
of  potassium  cyanide,  because  the  cyanide  formed  in  abund- 
ance on  the  anode  by  high  current-densities  cannot  with 
sufficient  rapidity  be  dissolved  by  the  potassium  cyanide.  In 
this  case,  recourse  must  also  be  had  to  scouring  the  anodes, 
and  then  increasing  the  anode-surfaces.  The  anodes  are  best 
suspended  to  the  anode-rods  by  means  of  copper  bands  riveted 
on. 

Execution  of  copper-plating. — The  general  rules  given  under 

/.nickeling,  as  regards  the  suitable  composition  of  the  bath, 


DEPOSITION    OF    COPPER,    BRASS    AND    BRONZE.  337 

correct  selection  of  anodes,  careful  scouring  and  pickling  of 
the  objects,  and  proper  current-strength  also  apply  to  copper- 
plating. 

In  copper  baths  containing  cyanide,  too  large  an  excess  of 
potassium  cyanide,  to  be  sure,  produces  an  evolution  of  hydro- 
gen-bubbles on  the  objects,  but  it  yields  either  no  deposit  at 
all  or  only  a  slight  one,  which  readily  peels'off.  If  this  phe- 
nomenon is  noticed  after  an  addition  of  potassium  cyanide  is 
made,  the  excess  has  to  be  removed  by  adding  a  copper  salt, 
best,  cupro-cupric  cyanide.  For  this  purpose  triturate  the 
latter  with  a  small  quantity  of  the  copper  bath  in  a  small  por- 
celain mortar  to  a  thinly-fluid  paste,  and  add  the  latter  to  the 
bath,  stirring  vigorously  for  some  time.  After  each  addition, 
see  whether  an  object  suspended  in  the  bath  becomes  rapidly 
and  properly  coppered  and,  if  such  be  not  the  case,  repeat 
the  addition  of  cupro-cupric  cyanide  until  the  bath  works  in 
a  faultless  and  correct  manner. 

However,  deposition  may  also  fail  by  reason  of  an  insuffi- 
cient addition  of  potassium  cyanide.  This  is  recognized  by 
the  heavy  formation  of  froth  on  the  anodes  and  the  appear- 
ance of  a  pale  blue  color  in  the  fluid,  though  this  may  also  be 
caused  by  the  content  of  rnetal  in  the  bath  being  too  small. 
While  in  the  first  case,  the  simple  addition  of  15  to  30  grains 
of  potassium  cyanide  per  quart  will  cause  the  bath  to  deposit 
in  the  proper  manner,  in  the  second  case,  solution  of  copper 
cyanide  in  potassium  cyanide  is  required  in  order  to  increase 
the  content  of  metal,  and  it  is  advisable  to  add  at  the  same 
time  a  small  quantity  of  carbonate  of  soda  and  of  bisulphite 
of  soda.  In  place  of  preparing  a  solution  of  copper  cyanide 
in  potassium  cyanide,  it  is  recommended  to  use  crystallized 
copper  cyanide,  which  can  be  obtained  from  manufacturers  of 
chemicals,  and  dissolve  it  in  hot  water. 

Many  platers  are  of  the  opinion  that  the  articles  to  be 
copper-plated  do  not  require  very  careful  cleaning  and  pick- 
ling before  plating,  because  this  is  supposed  to  be  sufficiently 
effected  by  the  baths  themselves,  by  those  containing  potas- 
22 


338  ELECTRO-DEPOSITION    OF    METALS. 

slum  cyanide,  as  well  as  by  those  with  alkaline  organic  com- 
binations. This  opinion,  however,  is  wrong.  It  is  true  the 
potassium  cyanide  dissolves  a  layer  of  oxide,  but  not,  or  at 
least  very  incompletely,  any  grease  present  upon  the  articles, 
and  hence  it  is  advisable  to  free  objects  intended  for  coppering 
as  thoroughly  from  grease  as  those  to  be  nickeled. 

The  preliminary  scouring  and  pickling  of  the  articles  to  be 
coppered  are  executed  according  to  the  directions  given  on  p. 
223.  The  same  precautions  referred,  to  under  "  Deposition  of 
Nickel  "  have  to  be  used  in  suspending  the  objects  in  the  bath, 
and  the  directions  given  there  for  the  suitable  arrangement  of 
the  anodes,  etc.,  also  apply  to  coppering.  However,  as  a  cop- 
per bath  conducts  better  than  a  nickel  bath,  the  distances 
between  the  anodes  and  the  objects  may,  if  necessary,  be  some- 
what greater. 

With  a  proper  arrangement  of  the  anodes  and  correct  regu- 
lation of  the  current,  the  objects  should  be  entirely  coated 
with  copper  in  a  few  minutes  after  being  suspended  in  the 
bath.  In  five  to  ten  minutes  the  objects  are  taken  from  the 
bath  and  brushed  with  a  scratch-brush  of  not  too  hard  brass 
wires,  whereby  the  deposit  should  everywhere  show  itself  to 
be  durable  and  adherent.  Defective  places  are  thoroughly 
scratch-brushed,  scoured,  and  pickled  ;  the  objects  are  then  re- 
turned to  the  bath.  For  solid  and  heavy  plating,  the  objects 
remain  in  the  bath  until  the  original  luster  and  red  tone  of 
the  coppering  disappear  and  pass  into  a  dull,  discolored 
brown.  At  this  stage  the  objects  are  again  scratch-brushed 
until  they  show  luster  and  the  red  copper  color,  and  in  doing 
this  it  is  of  advantage  to  moisten  them  with  tartar  water. 
They  are  then  again  returned  to  the  bath,  where  they  remain 
until  the  dull,  discolored  tone  reappears.  They  are  then 
taken  out,  scratch-brushed  bright,  rinsed  in  several  clean 
waters,  plunged  into  hot  water,  and  finally  dried,  first  in  saw- 
dust and  then  thoroughly,  at  a  high  temperature,  in  the  dry- 
ing chamber. 

Special  attention  must  be  paid  to  the  thorough  washing  o 


DEPOSITION    OF    COPPER,  BRASS    AND    BRONZE.  339 

the  coppered  objects,  because,  if  a  trace  of  the  bath  containing 
cyanide  remains  in  the  depressions  or  pores,  small,  dark,  round 
stains  appear  on  those  places,  which  cannot  be  removed,  or  at 
least  only  with  great  difficulty,  they  reappearing  again  in  a 
short  time  after  having  been  apparently  removed.  This  for- 
mation of  stains  appears  most  frequently  upon  coppered  (as 
well  as  brassed)  iron  and  zinc  castings,  which  cannot  be  pro- 
duced without  pores.  To  prevent  the  formation  of  these  stains 
the  following  method  is  recommended  :  Since  the  rinsing  in 
many  waters,  and  even  allowing  the  objects  to  lie  for  hours  in 
running  water,  offer  no  guarantee  that  every  trace  of  fluid 
containing  cyanide  has  been  removed,  the  objects  are  brought 
into  a  slightly  acid  bath  which  decomposes  the  fluid,  a  mix- 
ture of  1  part  of  acetic  acid  and  50  parts  of  water  being  well 
adapted  for  the  purpose.  The  objects  are  allowed  to  remain 
in  this  mixture  for  three  to  five  minutes,  when  they  are  rinsed 
off  in  water  and  dipped  for  a  few  minutes  in  dilute  milk  of 
lime.  They  are  finally  rinsed  and  dried.  Coppered  castings 
thus  treated  will  in  most  cases  show  no  stains. 

0.  Shultz  obtained  a  patent  for  the  following  method  for 
removing  the  hydrochloric  acid  from  the  pores,  and  for  pre- 
venting the  formation  of  stains:  The  plated  objects  are  placed 
in  a  room  which  can  be  hermetically  closed.  The  air  is  then 
removed  from  the  room  by  the  introduction  of  steam  of  a  high 
tension  and  by  means  of  an  air-pump,  and  water  is  sprinkled 
upon  the  objects.  By  this  treatment  in  vacuum  the  fluid 
in  the  pores  comes  to  the  surface,  and  the  salt  solution  is 
removed  by  the  water  sprinkled  over  the  articles. 

After  drying,  the  deposit  of  copper,  if  it  is  to  show  high 
luster,  is  polished  upon  soft  wheels  of  fine  flannel  and  dry 
Vienna  lime.  Commercial  rouge  FFF,  moistened  with  a  lit- 
tle alcohol,  is  also  an  excellent  polishing  agent  for  copper  and 
all  other  soft  metals. 

As  is  well  known,  massive  copper  rapidly  oxidizes  in  a 
humid  atmosphere,  and  this  is  the  case  to  a  still  greater 
extent  with  electro-deposited  copper.  Hence,  the  coppered 


340  ELECTRO-DEPOSITION    OF    METALS. 

objects,  if  they  are  not  to  be  further  coated  with  a  non-oxi- 
dizing metal,  have  to  be  provided  with  a  colorless,  transparent 
coat  of  lacquer. 

It  frequently  happens  that  slightly  coppered  (as  well  as 
slightly  brassed)  objects,  especially  of  zinc,  after  some  time, 
become  entirely  white  and  show  no  trace  of  the  deposit. 
This  is  due  to  the  deposit  penetrating  into  the  basis-metal,  as 
already  explained.  Lacquering  in  this  case  is  of  no  avail, 
the  deposit  also  disappearing  under  the  coat  of  lacquer.  The 
only  remedy  against  this  phenomenon  is  a  heavier  deposit. 

If  the  coppered  objects  are  to  be  coated  with  another  metal, 
drying  is  omitted,  and  after  careful  rinsing  they  are  directly 
brought  into  the  respective  bath,  or  into  the  quicking  pickle, 
if,  as  for  instance,  in  silvering,  quicking  has  to  be  done.  In 
such  cases,  where  the  copper  deposit  serves  only  as  an  inter- 
mediary for  the  reception  of  another  metallic  coating,  the 
objects  need  not  be  coppered  as  thickly,  as  previously  de- 
scribed, by  treating  them  three  times  in  the  bath.  Prelimi- 
nary coppering  for  5  to  10  minutes  suffices  in  all  cases,  which 
is  succeeded  by  scratch-brushing  in  order  to  be  convinced 
that  the  deposit  adheres  firmly,  and  that  the  basis-metal  is 
uniformly  coated.  The  objects  are  then  suspended  in  the 
bath  for  from  5  to  10  minutes  longer  with  a  weak  current. 

In  coppering  sheet-iron  or  sheet-zinc  which  is  to  be  nickeled, 
the  sheets  are  taken  from  the  bath  after  3  to  5  minutes,  at  any 
rate  while  they  still  retain  luster,  scratch-brushing  being  in 
this  case  omitted.  For  coppering  such  sheets  a  current-density 
of  0.5  ampere  and  an  electro-motive  force  of  3.5  to  4  volts  is 
required. 

The  treatment  of  copper  baths  when  they  become  inactive, 
or  show  other  abnormal  features,  has  already  been  referred  to. 

When,  as  is  frequently  done,  a  fluid  prepared  by  dissolving 
cuprous  oxide  in  potassium  cyanide  is  used  in  place  of  solu- 
tion of  crystallized  potassium  copper  cyanide  in  water,  for 
increasing  the  content  of  metal,  it  must  not  be  forgotten  to 
.add  the  corresponding  quantity  of  bisulphite  of  soda  for  the 


DEPOSITION    OF    COPPER,  BRASS    AND    BRONZE.  341 

conversion    of    the   caustic    potash    formed    into    potassium 
sulphate. 

All  other  general  rules  for  plating  baths  given  under 
"  Electro-plating  Solutions,"  Chapter  V.,  must  here  also  be 
observed. 

In  the  course  of  time,  copper-cyanide  baths  become  thick  in 
consequence  of  the  decomposition  of  the  potassium  cyanide 
and  the  accumulation  of  alkaline  carbonate  and  other  products 
of  transformation  formed  thereby,  the  additions  for  refreshing 
the  baths  also  partly  contributing  thereto.  While  the  normal 
specific  gravity  of  freshly  prepared  baths  is,  according  to  their 
composition,  from  5°  to  7°  Be.,  the  baths  after  having  been  in 
operation  for  several  years  may  show  11  °  Be.  and  more.  It  is 
frequently  found  that  coppering  in  baths  which  have  become 
thick  is  not  effectual,  the  deposit  not  adhering  so  well  and  not 
showing  the  brilliant  color  of  copper  as  when  produced  in  a 
fresh  bath.  The  only  remedy  for  this  is  diluting  the  bath 
with  water  to  6°  or  7°  Be.,  increasing  the  content  of  metal 
by  adding  highly  concentrated  solution  of  potassium  copper 
cyanide,  and  decomposing  the  alkaline  carbonates,  or  at  least 
a  greater  portion  of  them,  by  conducting  sulphurous  acid  into 
the  bath,  or  by  dissolving  bisulphite -of  soda  in  it. 

Coppering  small  articles  in  quantities.  If  a  large  quantity  of 
small  articles  is  at  one  time  to  be  coppered  in  dipping  baskets, 
it  is  recommended  to  use  the  baths  quite  hot,  this  causing,  to 
be  sure,  a  considerably  larger  consumption  of  potassium  cya- 
nide than  in  cold  baths.  For  the  rest  the  process  is  the  same 
as  that  given  for  nickeling  small  objects  in  quantities. 

If  very  large  quantities  of  small  articles  have  continually 
to  be  coppered,  one  of  the  mechanical  plating  contrivances 
referred  to  in  Chapter  VI  will  do  good  service. 

The  inlaying  of  depressions  of  coppered  art-castings  with 
black  may  be  done  in  different  ways.  Some  blacken  the 
ground  by  applying  a  mixture  of  spirit  lacquer  with  lamp- 
black and  graphite,  while  others  use  oil  of  turpentine  with 
lampblack  and  a  few  drops  of  copal  lacquer.  A  very  thin 


342  ELECTRO-DEPOSITION    OF    METALS. 

nigrosin  lacquer  mixed  with  finely  pulverized  graphite  is  very 
suitable  for  the  purpose.  When  the  lacquer  is  dry  the  ele- 
vated places  which  are  to  show  the  copper  color  are  cleansed 
with  a  linen  rag  moistened  with  alcohol. 

Electrolytically  coppered  articles  may  be  inlaid  black  by 
coating  them,  after  thorough  scouring  and  pickling,  with 
arsenic  in  one  of  the  baths  given  under  "  Electro-deposition  of 
Arsenic,"  and,  after  drying  in  hot  water  and  sawdust,  freeing 
the  surfaces  and  profiles,  which  are  to  appear  coppered,  from 
the  coating  of  arsenic  by  polishing  upon  a  felt  wheel.  If  this 
polishing  is  to  be  avoided,  the  portions  which  are  not  to  be 
black  may  be  coated  with  stopping-off  varnish,  and  arsenic 
deposited  upon  the  places  left  free. 

For  coppering  by  contact  and   boiling,  see   special   chapter, 

"  Depositions  by  Contact." 

For  coloring,  patinizing  and  oxidizing  of  copper,  see  the  proper 
chapter. 

Examination  of  Copper  Baths  Containing  Potassium  Cyanide. 

In  the  preceding  sections  several  characteristic  indications 
which  serve  for  the  qualitative  examination  of  these  baths  have 
already  been  given.  Like  all  baths  containing  potassium 
cyanide,  their  original  composition  gradually  suffers  extensive 
alterations  by  the  decomposition  of  the  potassium  cyanide, 
which  by  the  carbonic  acid  of  the  air  is  changed  to  potassium 
carbonate  and  hydrogen  cyanide,  and  spontaneously  also  to 
ammonia  and  potassium  formate.  The  potassium  cyanide  is 
also  split  up  by  the  current,  potassium  hydroxide  being 
formed,  together  with  decomposition  of  water,  which  by  the 
carbonic  acid  of  the  air  is  gradually  converted  into  potash, 
while  hydrogen  cyanide  and  hydrogen  escape.  Under  certain 
conditions  an  oxidation  of  the  potassium  cyanide  to  potassium 
cyanite  may  also  take  place. 

The  excess  of  potassium  cyanide  required  for  the  correct 
performance  of  the  copper  bath  is  therefore  gradually   con 
sumed,  and  the  bath,  at  first  of  a  wine-yellow  color,  acquires 


DEPOSITION    OF    COPPER,  BRASS    AND    BRONZE.  343 

a  blue  coloration,  and  does  no  longer  yield  a  good  deposit. 
When  such  is  the  case,  the  same  quantity  of  copper  which  is 
withdrawn  from  the  bath  by  the  deposit  is  not  dissolved  from 
the  anodes,  and  hence  the  determination  of  the  content  of  free 
potassium  cyanide,  as  well  as  that  of  the  content  of  copper, 
may  at  times  be  necessary.  A  determination  of  the  potassium 
carbonate  (potash)  formed  in  the  bath  and  its  removal,  or 
conversion  into  potassium  cyanide  by  the  addition  of  the  cor- 
responding quantity  of  barium  cyanide  solution,  which  will  be 
referred  to  under  silver  baths  cannot  be  recommended.  This 
determination  in  copper  baths  which  contain,  as  is  generally 
the  case,  sulphides,  is  troublesome,  and  an  accumulation  of 
potash  in  copper  baths  does  not  produce  the  same  evils  as  in 
a  silver  bath.  If,  however,  a  copper  bath,  after  working  for 
years,  has  become  thick  in  consequence  of  a  large  content  of 
potash,  it  can  be  renewed  without  considerable  expense,  or,  if 
this  is  not  desired,  it  can  be  regenerated  by  diluting  with 
water,  and  increasing  the  content  of  copper  and  of  potassium 
cyanide. 

Hence,  the  determination  of  the  free  potassium  cyanide 
(i.  e.,  not  fixed  on  copper)  and  that  of  the  copper  will  here 
only  be  discussed. 

Determination  of  potassium  cyanide. — The  best  and  most 
rapid  method  for  this  purpose  is  by  titrating  with  decinormal 
solution  of  silver  nitrate.  Silver  nitrate  and  potassium  cyanide 
form  finally  potassium  nitrate  and  insoluble  silver  cyanide,  the 
latter,  however,  being  redissolved  to  potassium  silver  cyanide 
so  long  as  free  potassium  cyanide  is  present.  Since  potassium 
silver  cyanide  contains  two  molecules  of  cyanogen,  one  mole- 
cule of  silver  nitrate  corresponds  to  two  molecules  of  potassium 
cyanide,  and  1  cubic  centimeter  of  decinormal  solution  of  sil- 
ver nitrate  corresponds  to  0.013  gramme  of  potassium  cyanide. 

Bring,  by  means  of  a  pipette,  5  cubic  centimeters  of  the 
copper  bath  into  a  beaker  having  a  capacity  of  about  J  liter. 
Dilute  with  about  150  cubic  centimeters  of  water,  add  one  or 
two  drops  of  saturated  common  salt  solution,  and  then,  whilst 


344  ELECTRO-DEPOSITION    OF,  METALS. 

constantly  stirring  the  fluid  in  the  beaker,  allow  to  flow  in  from 
the  burette  silver  nitrate  solution  so  long  as  the  precipitate 
formed  dissolves  rapidly. 

When  solution  becomes  sluggish,  add,  stirring  constantly? 
silver  nitrate  solution  drop  by  drop,  waiting  after  the  addition 
of  each  drop  until  the  fluid  has  again  become  clear.  When 
the  fluid  does  not  become  clear  after  adding  the  last  drop,  and 
it  shows  a  slight  turbidity,  no  more  free  potassium  cyanide  is 
present.  By  multiplying  the  cubic  centimeters  of  decinormal 
solution  of  silver  nitrate  used  by  2.6  the  content  of  potassium 
cyanide  per  liter  of  bath  is  found. 

Suppose,  for  instance,  for  5  cubic  centimeters  of  bath,  2.2 
cubic  centimeters  of  silver  solution  have  been  used,  then  1 
liter  of  the  bath  contains  2.2  X  2.6  =  5.72  grammes  of  free 
potassium  cyanide,  because  1  cubic  centimeter  of  silver  solu- 
tion corresponds  to  0.013  grammes  of  potassium  cyanide, 
therefore  2.2  cubic  centimeters  =  2.2  X  0.013  =  0.0286 
grammes,  from  which  results  by  calculation 

5  :  0.0286  =  100  :  x 


x  =  5.72  grammes. 

If  now  the  initial  content  of  free  potassium  cyanide  in  the 
freshly  prepared  bath  has  been  determined,  a  later  determina- 
tion will  show  the  deficiency  of  it  which  has  come  about.  It 
must,  however,  be  taken  into  consideration  that  the  potassium 
formate  formed  by  the  decomposition  of  the  potassium  cyanide 
may,  up  to  a  certain  degree,  apparently  fill  the  role  of  the 
potassium  cyanide,  in  so  far  as  it  decreases  the  conducting  re- 
sistance of  the  bath,  but  it  does  not  contribute  to  the  solution 
of  the  anodes.  Hence,  if  the  established  deficiency  of  potas- 
sium cyanide  would  be  replaced  by  equally  large  quantities  of 
the  salt,  there  would  be  danger  of  too  much  of  it  getting  into 
the  bath,  and  the  latter  would  conduct  too  readily,  which 
would  result  in  the  deposit  precipitating  too  rapidly  and 
turning  out  less  adherent. 


DEPOSITION    OF    COPPER,  BRASS    AND    BRONZE.  345- 

Hence  it  is  evident  that  analytical  methods  alone  are  not 
sufficient  for  maintaining  entirely  constant  baths  containing 
potassium  cyanide,  and  practical  experience  and  a  good  fac- 
ulty of  observation  are  required  if  the  results  of  analysis  are 
to  be  utilized  for  the  correction  of  the  baths.  The  potassium 
formate  can  neither  be  removed  from  the  bath  nor  can  it  be 
quantitatively  determined,  and  since  its  action  in  the  bath  i& 
not  accurately  known,  it  can  only  be  stated  from  practical 
experience,  that  under  normal  conditions  only  about  60  per 
cent,  of  the  deficiency  of  free  potassium  cyanide  in  a  copper 
bath  should  be  replaced  by  pure  potassium  cyanide. 

Determination  of  copper.  This  may  be  effected  by  electro- 
lytic or  volumetric  analysis. 

For  the  determination  of  copper  by  electrolysis,  measure  off  by 
means  of  the  pipette,  10  cubic  centimeters  of  the  copper  bath,, 
and  allow  the  fluid  to  run  into  a  porcelain  dish  having  a  ca- 
pacity of  150  to  200  cubic  centimeters.  Add  10  cubic  centi- 
meters of  pure,  strong  hydrochloric  acid,  cover  the  dish  with  a 
watch-glass  and  heat  upon  the  water-bath.  When  evolution  of 
gas  ceases,  carefully  remove  the  watch-glass,  rinse  off  adhering 
drops  with  a  small  quantity  of  distilled  water  into  the  dish,  and 
evaporate  the  contents  of  the  latter  nearly  to  dryness.  Now  add 
about  1  cubic  centimeter  of  strong  nitric  acid,  swing  the  dish  to 
and  fro  so  that  all  portions  of  the  residue  are  moistened  by  the 
acid,  heat  for  a  short  time,  and  then  add  32  cubic  centimeter& 
of  pure  dilute  sulphuric  acid  (1  part  acid,  2  parts  water),  with 
which  the  contents  of  each  dish  are  heated,  until  every  trace  of 
odor  of  hydrochloric  and  nitric  acids  has  disappeared.  Now 
pour  the  copper  solution  into  the  platinum  dish  serving  for 
electrolysis,  rinse  the  porcelain  dish  with  distilled  water,  add- 
ing the  wash-water  to  the  contents  of  the  platinum  dish,  fill 
the  latter  up  to  within  1  centimeter  of  the  rim  with  water, 
add  2  cubic  centimeters  of  pure  concentrated  nitric  acid,  and 
electrolyze  with  a  current-strength  of  ND  100  =  1  ampere,  i.  e.r 
1  ampere  for  100  square  centimeters  surface  of  the  platinum 
dish  which  serves  as  cathode. 


346  ELECTRO-DEPOSITION    OF    METALS. 

The  copper  separates  with  a  bright  red  color,  adhering 
firmly  to  the  platinum  dish,  which  is  connected  with  the  neg- 
ative pole  of  the  source  of  current.  That  the  separation  of 
copper  is  finished  is  recognized  by  a  narrow  strip  of  platinum 
sheet,  when  suspended  in  the  platinum  dish,  showing  in  15 
minutes  no  trace  of  coppering ;  or  by  a  few  drops  of  the  solu- 
tion when  brought  together  with  a  drop  of  yellow  prussiate  of 
potash  solution,  producing  no  red  coloration. 

When  by  one  of  the  above-mentioned  means  the  complete 
separation  of  the  copper  has  been  ascertained,  the  platinum 
dish  is  washed,  without  interruption  of  the  current,  the  water 
removed  by  rinsing  the  dish  with  absolute  alcohol,  and  the 
latter  removed  by  rinsing  with  ether.  Dry  for  a  short  time  in 
an  air-bath  at  212°  F.,  and  weigh  the  dish  together  with  the 
precipitate  of  copper.  By  deducting  the  weight  of  the  dish, 
the  weight  of  the  copper  is  obtained,  and,  since  10  cubic  centi- 
meters of  the  bath  were  electrolyzed,  the  weight  of  the  copper 
multiplied  by  100  gives  the  contents  of  copper  in  grammes  in 
1  liter  of  copper  bath. 

The  volumetric  determination  of  copper  is  based  upon  the 
principle  that  solution  of  sulphate  or  chloride  of  copper  forms 
with  potassium  iodide,  copper  iodide,  whilst  free  iodine  is  at 
the  same  time  formed,  one  atom  of  liberated  iodine  corres- 
ponding to  one  molecule  of  copper  salt.  This  free  iodine  is 
determined' by  titration  with  a  solution  of  sodium  hyposulphite 
of  known  content,  and  the  content  of  copper  is  calculated  from 
the  number  of  cubic  centimeters  of  the  solution  used.  For  the 
recognition  of  the  final  reaction,  the  blue  coloration,  which 
originates  when  starch  solution  combines  with  free  iodine,  is 
utilized.  There  are  required  a  decinormal  iodine  solution 
which  contains  per  liter  exactly  12.7  grammes  of  re-sublimated 
iodine  dissolved  in  potassium  iodide,  and  a  decinormal  solu- 
tion of  sodium  hyposulphite,  of  which  10  cubic  centimeters 
diluted  with  water  and  compounded  with  a  small  quantity 
of  starch  solution  must  exactly  use  10  cubic  centimeters  of 
iodine  solution  to  give  a  permanent  blue  coloration  by  the 
formation  of  iodine-starch. 


DEPOSITION    OF    COPPER,   BRASS    AND    BRONZE.  347 

The  mode  of  operation  is  as  follows :  Heat  in  a  porcelain 
-dish  10  cubic  centimeters  of  the  copper  bath  with  10  cubic 
centimeters  of  strong  hydrochloric  acid,  evaporate  nearly  to 
dryness  with  1  cubic  centimeter  of  strong  nitric  acid  and  2 
cubic  centimeters  of  hydrochloric  acid,  and  heat  upon  the 
water-bath  until  the  nitric  acid  is  entirely  removed.  The  resi- 
due is  dissolved  in  water  with  the  addition  of  a  small  quantity 
of  dilute  hydrochloric  acid.  The  clear  solution  is  brought  into 
a  measuring  flask  holding  100  cubic  centimeters,  the  dish  is 
rinsed  with  water,  the  free  acid  neutralized  by  the  addition  of 
dilute  soda  lye  until  a  precipitate  of  bluish  copper  hydrate 
commences  to  separate,  which  after  vigorous  shaking  does  not 
disappear.  Now  add,  drop  by  drop,  hydrochloric  acid  until 
the  precipitate  just  dissolves,  fill  the  flask  up  to  the  100-centi- 
meter mark  with  water,  and  mix  by  shaking.  Of  this  solu- 
tion bring  by  means  of  the  pipette,  10  cubic  centimeters  into 
a  glass  of  100  cubic  centimeters  capacity,-  and  provided  with 
#  glass  stopper,  add  10  cubic  centimeters  of  a  10  per  cent, 
potassium  iodide  solution,  dilute  with  a  small  quantity  of 
water,  close  the  glass  with  the  stopper,  and  let  it  stand  for  10 
•minutes.  Now  add  from  a  burette,  decinormal  solution  of 
sodium  hyposulphite  until  the  iodine  solution  has  become 
-colorless,  and  then  add  a  few  cubic  centimeters  more.  Next 
bring  into  the  flask  a  few  drops  of  starch  solution,  and  then 
add  from  another  burette,  decinormal  iodine  solution  until  a 
blue  coloration  is  just  perceptible.  By  deducting  the  cubic 
centimeters  of  iodine  solution  used  from  the  cubic  centimeters 
-of  sodium  hyposulphite  solution,  it  will  be  known  how  many 
•cubic  centimeters  of  the  latter  solution  have  been  used  for 
fixing  the  iodine  liberated  by  the  reciprocal  action  between 
•copper  solution  and  potassium  cyanide  solution.  Since  1  cubic 
•centimeter  of  a  sodium  hyposulphite  solution,  which  is  equiva- 
lent to  the  decinormal  iodine  solution,  corresponds  to  0.0063 
gramme  of  copper,  therefore,  as  1  cubic  centimeter  of  the  bath 
has  been  titrated,  the  number  of  cubic  centimeters  found  has 
to  be  multiplied  by  6.3  to  find  the  content  of  copper  per  liter 
of  copper  bath. 


348  ELECTRO-DEPOSITION    OF    METALS. 

Suppose  to  10  cubic  centimeters  of  the  copper  solution 
mixed  with  potassium  iodide  has  been  added  2.8  cubic  centi- 
meters of  sodium  hyposulphite  solution,  and  for  titrating  back 
the  excess  0.7  cubic  centimeters  of  iodine  solution  had  been 
used  up  to  the  appearance  of  the  blue  coloration,  then  2.8  — 
0.7  =  2.1  centimeters  have  been  used,  which  multiplied  by 
6.3  gives  13.23  grammes  as  the  content  of  copper  per  liter  of 
bath. 

If  now  a  deficiency  of  copper  has  been  established  by  one 
or  the  other  method,  the  original  content  of  copper  can  be 
readily  restored  by  the  addition  of  crystallized  potassium- 
copper  cyanide.  This  salt,  when  pure,  contains  about  30  per 
cent,  copper. 

Suppose,  when  first  prepared,  the  bath  contained  15  grammes- 
of  copper  per  liter,  and  it  has  been  shown  by  analysis  that  it 
now  contains  only  13.3  grammes,  then  a  deficiency  of  1.7 
grammes  of  copper  has  to  be  made  up.  Since  100  grammes 
of  potassium-copper  cyanide  contain  30  grammes  of  copper, 
then 

3  :  100  =  1.7  ix 
x  =  3.57 

and  hence  3.57  grammes  of  potassium-copper  cyanide  per  liter 
have  to  be  dissolved  in  the  bath.  It  is  advisable  to  electro- 
lytically  determine  in  the  previously  described  manner,  after 
first  destroying  the  cyanogen  combinations,  the  content  of 
copper  in  the  potassium-copper  cyanide  to  be  used  for  strength- 
ening the  bath,  so  that  in  case  the  salt  shows  a  smaller  con- 
tent of  copper,  the  proper  quantity  of  it  may  be  added. 

2.   DEPOSITION  OF  BRASS. 

Brass  is  an  alloy  of  copper  and  zinc,  whose  color  depends 
on  the  quantitative  proportions  of  both  metals.  The  alloys 
known  as  yellow  brass,  red  brass  (similar,  tombac),  consist  es- 
sentially of  copper  and  zinc,  while  those  known  as  bell  metal} 
gun  metal,  and  the  bronzes  of  the  ancients  are  composed  of  copper 
and  tin.  Modern  bronzes  contain  copper,  zinc  and  tin. 


DEPOSITION    OF    COPPER,  BRASS    AND    BRONZE.  349 

The  behavior  of  brass  towards  acids  is  nearly  the  same  as 
that  of  copper.  It  oxidizes,  however,  less  rapidly  in  the  air, 
is  harder  than  copper,  malleable,  and  can  be  rolled  and  drawn 
into  wire. 

Brass  baths.  In  accordance  with  the  plan  pursued  in  this 
work  only  the  most  approved  formulas,  the  greater  portion  of 
which  has  been  practically  tested,  will  be  given.  More  recent 
propositions  which  cannot  be  recognized  as  improvements 
over  the  older  directions,  will  be  critically  commented  upon. 
There  is  a  large  number  of  receipts  for  brass  baths  which 
show  such  remarkable  difference  in  the  proportions  of  the  two 
metals  that,  on  more  closely  examining  them,  even  the  layman 
can,  at  the  first  glance,  discover  the  doubtful  result.  Thus, 
for  instance,  Russell  and  Woolrich  recommend  a  bath  in 
which  the  quantity  of  copper  salt  to  zinc  salt  is  in  the  pro- 
portion of  10:1.  Other  authors  give  the  following  propor- 
tions :  Copper  1  to  zinc  8  (Heeren) ;  copper  1  to  zinc  2  (Sal- 
zede,  Kruel);  copper  2  to  zinc  1  (Newton).  These  examples 
will  show  the  difference  of  opinion  regarding  the  suitable 
composition  of  brass  baths. 

An  electro-plater  understanding  all  the  conditions  and  the 
effect  of  the  current-strength  might  possibly  obtain  a  deposit 
of  brass  even  from  baths  which  show  such  abnormal  propor- 
tions of  mixture  as  those  made  up  according  to  the  directions 
by  Russell,  Heeren,  and  others,  but  how  many  conditions  have 
thereby  to  be  taken  into  consideration  will  be  shown  later  on. 
We  share  the  opinion  of  Roseleur  that  a  brass  bath  containing 
•copper  and  zinc  salts  in  nearly  equal  proportions  is  the  most 
suitable  and  least  subject  to  disturbances.  A  brass  bath  is  to 
be  considered  as  a  mixture  of  solutions  of  copper  cyanide  and 
zinc  cyanide,  or  of  other  copper-zinc  salts,  in  the  most  suitable 
solvent.  Now,  since  a  solution  of  copper  cyanide  requires  a 
•different  current-strength  from  one  of  zinc  salt,  it  will  be  seen 
that  according  to  the  greater  or  smaller  current-strength,  now 
more  of  the  one,  and  now  more  of  the  other,  metal  is  depos- 
ited, which,  of  course,  influences  the  color  of  the  deposit. 


350  ELECTRO-DEPOSITION    OF    METALS. 

Hence  the  proper  regulation  of  the  current  is  the  chief  condi- 
tion for  obtaining  beautiful  deposits,  let  the  bath  be  composed, 
as  it  may. 

For  all  baths  containing  more  than  one  metal  in  solution,  it 
may  be  laid  down  as  a  rule  that  the  less  positive  metal  is  first 
deposited.  In  a  brass  bath,  copper  is  the  negative,  and  zinc 
the  positive  metal ;  and  hence  a  weaker  current  deposits  more 
copper,  in  consequence  of  which  the  deposit  becomes  redder, 
while,  vice  versa,  a  more  powerful  current  decomposes,  in  addi- 
tion to  the  copper  solution,  also  a  larger  quantity  of  zinc  solu- 
tion, and  reduces  zinc,  the  color  produced  being  more  pale 
yellow  to  greenish.  By  bearing  this  in  mind  it  is  not  difficult 
to  obtain  any  desired  shades  within  certain  limits. 

I.  Brass  bath  according  to  Roseteur. — Blue  vitriol  and  zinc 
sulphate  (white  vitriol),  of  each  5J  ounces,  and  crystallized 
carbonate  of  soda  15}  ounces.  Crystallized  carbonate  of 
soda  and  bisulphite  of  soda  in  powder,  of  each  7  ounces,  98 
per  cent,  potassium  cyanide  8f  ounces,  arsenious  acid  30f 
grains,  water  10  quarts. 

Electro-motive  force  at  10  cm.  electrode-distance,  2.6.  to  2.8 
volts. 

Current-density,  0.32  ampere. 

The  bath  is  prepared  as  follows  :  In  5  quarts  of  warm  water 
dissolve  the  blue  vitriol  and  the  zinc  sulphate ;  and  in  the 
other  5  quarts  the  15  j  ounces  of  carbonate  of  soda  ;  then  mix 
both  solutions,  stirring  constantly.  A  precipitate  of  car- 
bonate of  copper  and  carbonate  of  zinc  is  formed,  which  is 
allowed  quietly  to  settle  for  10  to  12  hours,  when  the  super- 
natant clear  fluid  is  carefully  poured  off,  so  that  nothing  of 
the  precipitate  is  lost.  Washing  the  precipitate  is  not  neces- 
sary. The  clear  fluid  poured  off  is  of  no  value  and  is  thrown 
away.  Now  add  to  the  precipitate  so  much  water  that  the 
resulting  fluid  amounts  to  about  6  quarts,  and  dissolve  in  it, 
with  constant  stirring,  the  carbonate  and  bisulphite  of  soda, 
adding  these  salts,  however,  not  at  once,  but  gradually,  in 
small  portions,  to  avoid  foaming  over  by  the  escaping  car- 


DEPOSITION    OP    COPPER,  BRASS    AND    BRONZE.  351 

bonic  acid.  Dissolve  the  potassium  cyanide  in  4  quarts  of 
cold  water  and  add  this  solution,  with  the  exception  of  about 
J  pint  in  which  the  arsenious  acid  is  dissolved  with  the  assist- 
ance of  heat,  to  the  first  solutions,  and  finally  add  the  solution 
of  arsenious  acid  in  the  J  pint  of  water  retained,  when  the 
bath  should  be  clear  and  colorless.  If  after  continued  stir- 
ring, particles  of  the  precipitate  remain  undissolved,  carefully 
add  somewhat  more  potassium  cyanide  until  solution  is 
complete. 

The  addition  of  a  small  quantity  of  arsenious  acid  is  claimed 
to  make  the  brassing  brighter  ;  but  the  above-mentioned  pro- 
portion of  30f  grains  for  a  10-quart  bath  must  not  be  ex- 
ceeded, as  otherwise  the  color  of  the  deposit  would  be  too 
light  and  show  a  gray  tone. 

II.  Crystallized  carbonate  of  soda  10J  ounces,  pulverized 
bisulphite  of  soda  7  ounces,  neutral  copper  acetate  4.4  ounces, 
pulverized  chloride  of  zinc  4.4  ounces,  98-per  cent,  potassium 
cyanide  14.11  ounces,  arsenious  acid  30f  grains,  water  10 
quarts. 

Electro-motive  force  at  10  cm.  electrode-distance  2.6  to  2.8 
volts. 

Current  density  0.32  ampere. 

The  preparation  of  this  bath  is  more  simple  than  that  of  the 
preceding. 

Dissolve  the  carbonate  and  bisulphite  of  soda  in  4  quarts  of 
water,  then  mix  the  acetate  of  copper  and  chloride  of  zinc  with 
2  quarts  of  water,  and  gradually  add  this  mixture  to  the  solu- 
tion of  the  soda  salts.  Next  dissolve  the  potassium  cyanide  in 
4  quarts  of  water,  and  add  this  solution  to  the  first,  retaining, 
however,  a  small  portion  of  it,  in  which  dissolve  the  arsenious 
acid  with  the  assistance  of  heat.  Finally  add  the  arsenious 
acid  solution,  when  the  bath  will  become  clear.  If,  however, 
the  solution  should  not  be  clear  and  colorless,  or  at  least  wine- 
yellow,  after  adding  the  potassium  cyanide,  an  additional 
small  quantity  of  the  latter  may  be  used,  avoiding,  however, 
a  considerable  excess. 


352  ELECTRO-DEPOSITION    OF    METALS. 

For  brassing  iron  in  this  bath,  the  quantity  of  carbonate  of 
soda  may  be  increased  up  to  35  ozs.  for  a  10-quart  bath.  This 
is  also  permissible,  when  in  plating  zinc  articles  with  a  heavy 
deposit  of  brass,  frequent  scratch-brushing  is  to  be  avoided. 
It  would  seem  that  a  large  content  of  carbonate  of  soda  in  the 
bath  retards  to  a  considerable  extent  the  brass  color  from 
changing  into  a  discolored  brown,  though  the  brilliancy  of  the 
deposit  appears  to  suffer  somewhat.  When  boiled  for  1  to  2 
hours,  or  worked  through  with  the  current  for  10  to  12  hours, 
the  bath  prepared  according  to  formula  If.  works  very  well. 

Cupro-cupric  sulphide  and  cuprous  oxide  may  also  be  ad- 
vantageously used  for  the  preparation  of  brass  baths.  Suitable 
formulas  for  them  are  as  follows : 

Ila.  Pure  crystallized  zinc  sulphate  (zinc  vitriol  or  white 
vitriol)  5J  ozs.,  crystallized  carbonate  of  soda  7  ozs.,  pulverized 
bisulphite  of  soda  4J  ozs.,  ammonium-soda  5J  ozs.,  99  per 
cent,  potassium  cyanide  10 J  ozs.,  cupro-cupric  sulphide  3-J- 
ozs.,  water  10  quarts. 

Electro-motive  force  at  10  cm.  electrode-distance,  2.8  volts. 

Current- density,  0.5  ampere. 

The  bath  is  prepared  as  follows :  Dissolve  the  zinc  sulphate 
in  5  quarts  of  water  and  the  crystallized  carbonate  of  soda  in 
4  quarts  of  warm  water,  and  mix  the  two  solutions.  When 
the  precipitate  of  zinc  carbonate,  whiclV  is  formed,  has  com- 
pletely settled,  siphon  off  the  supernatant  fluid  as  much  as 
possible,  and  throw  the  lye  away. 

Dissolve  the  bisulphite  of  soda,  the  ammonium-soda,  and 
the  potassium  cyanide  in  5  quarts  of  water,  add  the  cupro- 
cupric  sulphide,  stirring  constantly,  and  when  solution  is  com- 
plete, add  the  precipitate  of  zinc  carbonate. 

This  bath  yields  beautiful  pale  yellow  deposits  of  a  warm 
brass  tone. 

116.  Potassium  cyanide  10J  ozs.,  cuprous  oxide  3  ozs.,  zinc 
chloride  2}  ozs.,  bisulphite  of  soda  7  ozs.,  water  10  quarts. 

Dissolve  the  potassium  cyanide  in  5  quarts  of  water,  add 
the  cuprous  oxide  and  stir  until  solution  is  complete.  Dis- 


DEPOSITION    OF    COPPER,   BRASS    AND    BRONZE.  353 

solve  the  bisulphite  of  soda  and  the  zinc  chloride  in  the  other  5 
quarts  of  water,  and  mix  the  two  solutions,  stirring  vigorously. 
If  metallic  cyanides  are  to  be  used  for  the  preparation  of 
brass  baths,  the  following  formula  may  be  recommended  : 

III.  Crystallized    carbonate   of  soda   10J   ozs.,   pulverized 
bisulphite  of  soda  7  ozs.,  copper  cyanide  and  zinc  cyanide  of 
each  3J  ozs.,  water  10  quarts,  and  enough  98  per  cent,  potas- 
sium cyanide  to  render  the  solution  clear. 

To  prepare  the  bath  dissolve  the  carbonate  and  bisulphite 
of  soda  in  2  or  3  quarts  of  water,  rub  in  a  porcelain  mortar 
the  copper  cyanide  and  zinc  cyanide  with  a  quart  of  water  to 
a  thin  paste,  add  this  paste  to  the  solution  of  the  soda  salts, 
and  finally  add,  with  vigorous  stirring,  concentrated  potas- 
sium cyanide  solution  until  the  metallic  cyanides  are  dissolved. 
Dilute  the  volume  to  10  quarts,  and,  for  the  rest,  proceed  as 
given  for  formulas  I  and  II. 

Brass  baths  may  in  a  still  more  simple  manner  be  prepared 
by  using  the  double  cyanides,  potassium-cupric  cyanide  and 
potassium-zinc  cyanide. 

Ilia.  Potassium-cupric  cyanide  (crystallized)  5J  ozs.,  potas- 
sium-zinc cyanide  (crystallized)  5}  ozs.,  crystallized  bisul- 
phite of  soda  8{  ozs.,  98  per  cent,  potassium  cyanide  11 J 
drachms,  water  10  quarts. 

Electro-motive  force  at  10  cm.  electrode-distance,  3  volts. 

Current- density,  0.3  ampere. 

The  bath  is  prepared  by  simply  dissolving  the  salts  in  warm 
water  of  about  122°  F. 

For  brassing  zinc  exclusively,  Roseleur  recommends  the  fol- 
lowing bath  : 

IV.  Dissolve  9f  ozs.  of  crystallized  bisulphite  of  soda  and 
14  ozs.  of  70  per  cent,  potassium  cyanide  in  8  quarts  of  water, 
and  add  to  this  solution  one  of  4  j  ozs.  each  of  neutral  copper 
acetate  and  crystallized  chloride  of  zinc,  5J  ozs.  of  aqua  am- 
monia of  0.910  specific  gravity,  and  2  quarts  of  water. 

For  brassing  wrong  Jit-iron,  cast-iron  and  steel,  Gore  highly 
recommends  the  following  composition  : 
23 


354  ELECTRO-DEPOSITION    OF    METALS. 

IVa.  Dissolve  35 J  ozs.  of  crystallized  carbonate  of  soda,  7 
ozs.  of  pulverized  bisulphite  of  soda,  13J  ozs.  of  98  per  cent, 
potassium  cyanide  in  8  quarts  of  water ;  then  add,  stirring 
constantly,  a  solution  of  fused  chloride  of  zinc  3J  ozs.,  and 
neutral  copper  acetate  4J  ozs.,  in  2  quarts  of  water.  Boil  and 
filter.  The  bath  works  well,  best  with  an  electro-motive  force 
of  3.75  volts,  and  also  takes  readily  on  cast-iron. 

A  solution  for  transferring  any  copper-zinc  alloy  which  serves  as 
anode,  is  composed,  according  to  Hess,  as  follows : 

V.  Sodium  bicarbonate,  14|  ozs.,  crystallized  ammonium 
chloride  9J  ozs.,  98  per  cent,  potassium  cyanide  2J  ozs.,  water 
10  quarts. 

Cast  metal  plates  are  to  be  used  as  anodes.  Transfer  begins 
after  a  current  of  medium  strength  has  for  a  few  hours  passed 
through  the  bath. 

This  bath  is  also  well  adapted  for  the  deposition  of  tombac 
with  the  use  of  tombac  anodes.  Most  suitable  electro-motive 
force,  3  to  3.5  volts. 

Fresh  brass  baths  work,  as  a  rule,  more  irregularly  than  any 
other  baths  containing  cyanide,  the  deposit  being  either  too 
red  or  too  green  or  gray,  while  frequently  one  side  of  the  ob- 
ject is  coated  quite  well,  and  the  other  not  at  all.  To  force 
the  bath  to  work  correctly  it  must  be  thoroughly  boiled,  the 
water  which  is  lost  by  evaporation  being  replaced  by  the  ad- 
dition of  distilled  water  or  pure  rain  water.  If  boiling  is  to 
be  avoided,  the  bath,  as  previously  mentioned,  is  worked 
through  for  hours,  and  even  for  days,  with  the  current,  until 
an  object  suspended  in  it  is  correctly  brassed. 

Prepared  brass  salts.  Regarding  these  salts,  we  refer  to  what 
has  been  said  in  reference  to  coppering  salts,  p.  332.  For  a 
100-quart  brass  bath,  with  92.59  grains  of  brass,  use  6.6  Ibs. 
of  double  brass  salt  and  7  ozs.  of  98  to  99  per  cent,  potassium 
cyanide,  and  for  a  100-quart  brass  bath  with  138.88  grains  of 
brass  per  quart  9.9  Ibs.  of  brass  double  salt  and  7  ozs.  of  98  to 
99  per  cent,  potassium  cyanide. 

As  for  copper  baths  prepared  with  double  salts,  an  addition 


DEPOSITION    OF    COPPER,  BRASS    AND    BRONZE.  355 

of  30  to  46  grains  of  potassium  cyanide  per  liter  and  of  a  suit- 
able conducting  salt  (neutral  sodium  sulphite)  may  be  recom- 
mended. 

Tanks  for  brass  baths.  What  has  been  said  on  this  subject 
under  tanks  for  copper  cyanide  baths  (p.  335)  applies  also  to 
brass  baths. 

Brass  anodes.  Sheets  of  brass,  annealed  and  pickled  bright, 
not  rolled  too  hard  and  of  as  nearly  as  possible  the  same  com- 
position and  color  as  the  deposit  is  to  have,  are  used  as  anodes. 

Cast  anodes  have  the  advantage  of  being  more  readily  solu- 
ble, and  therefore  keep  the  content  of  metal  in  the  bath  more 
constant  than  rolled  brass  anodes.  However,  the  latter  answer 
very  well  if  care  is  taken  to  from  time  to  time  increase 
the  content  of  metal  in  the  bath.  The  anode-surface  in  the 
bath  should  be  as  large  as  possible,  since  with  slight  anode 
current-densities  the  formation  of  slime  on  the  anodes  is  less 
than  when  the  contrary  is  the  case. 

Execution  of  brassing.  As  previously  mentioned,  the  color 
of  the  deposits  depends  on  the  quantitative  proportions  of  the 
two  metals  deposited,  a  weaker  current  depositing  predomi- 
nantly copper,  and  a  stronger  current  more  zinc.  Hence  by 
the  use  of  a  rheostat  it  is  in  the  power  of  the  operator  to  effect 
within  the  limits  which  are  given  by  the  resistances  of  the 
rheostat,  deposits  of  brass  alloys  of  a  redder  or  more  pale 
yellow  to  greenish  color,  according  to  whether  the  resistance 
is  increased  or  decreased. 

However,  according  to  the  composition  of  the  brass  bath, 
and  especially  with  baths  which  have  for  a  long  time  been  in 
use,  a  determined  color  of  the  alloy  to  be  deposited  cannot  be 
produced  with  the  assistance  of  the  rheostat.  In  such  case  the 
content  of  metal  in  the  bath  which  is  required  and  lacking  for 
the  production  of  a  determined  color,  must  be  augmented  by 
the  addition  of  solution  of  the  respective  metallic  salts,  or  in 
the  form  of  double  salt. 

Suppose  a  bath  which  originally  contained  copper  and  zinc 
salts  in  equal  proportions  has  been  long  in  daily  use.  Now, 


356  ELECTRO-DEPOSITION    OF    METALS. 

since  brass  contains  more  copper  than  zinc  the  deposit  will  be 
richer  in  copper,  and  it  is  evident  that  more  of  the  latter  will 
be  withdrawn  from  the  bath  than  of  zinc,  and  finally  a  limit 
will  be  reached  when  the  bath  with  a  current  suitable  for  the 
decomposition  of  the  solution  will  deposit  a  greenish  or  gray 
brass,  and  with  a  weaker  current  produce  no  deposit  whatever. 
The  only  remedy  in  such  a  case  is  the  addition  of  sufficient 
solution  of  copper  cyanide  in  potassium  cyanide,  so  that,  even 
with  quite  a  powerful  current,  a  deposit  of  a  beautiful  brass 
color  is  produced,  the  shades  of  which  can  then  again  be  con- 
trolled with  the  assistance  of  the  rheostat.  Instead  of  dissolv- 
ing copper  cyanide  in  potassium  cyanide,  it  is  better  to  directly 
use  crystallized  potassium-copper  cyanide.  However,  it  must 
not  be  forgotten  that  every  addition  of  a  metallic  salt  momen- 
tarily irritates  the  brass  bath,  making  it,  so  to  say,  sick,  and  to 
confine  this  feature  to  the  narrowest  limit,  an  addition  of  car- 
bonate and  bisulphite  of  soda,  or  only  of  neutral  bisulphite  of 
soda,  should  at  the  same  time  be  made,  and  the  bath  be 
worked  thrpugh  with  the  current  as  previously  described,  until 
a  test  shows  that  it  works  in  a  regular  manner.  The  effect  of 
the  addition  cannot  be  controlled  in  any  other  way,  and  more 
might  be  added  than  is  required  and  desirable.  If,  however, 
the  quantity  of  the  addition  is  shown  not  to  be  sufficient,  the 
operation  is  continued  till  the  object  is  attained. 

As  in  the  copper  bath,  an  abundant  formation  of  slime  on 
the  anodes  indicates  the  want  of  potassium  cyanide  in  the  bath. 
In  this  case  the  evolution  of  gas-bubbles  on  the  objects  is  very 
slight,  and  the  deposit  forms  slowly.  This  is  remedied  by  an 
addition  of  potassium  cyanide.  However,  in  brass  baths  con- 
taining the  standard  excess  of  free  potassium  cyanide,  the  for- 
mation of  slime  has  also  a  disturbing  effect,  when  the  baths 
are  for  a  longer  time  worked  without  interruption.  The  solu- 
tion by  the  potassium  cyanide  of  the  bath  of  the  metallic 
cyanides  formed  on  the  anodes  takes  place  more  slowly  than 
their  formation.  If  the  operation  of  the  bath  is  for  some  time 
interrupted,  gradual  solution  takes  place  and  the  greater  part 


DEPOSITION    OF    COPPER,  BRASS    AND    BRONZE.  357 

r 

of  the  slime  on  the  anodes  disappears.  However,  with  an  un- 
interrupted use  of  the  bath,  the  layer  of  slime  frequently  in- 
creases to  such  an  extent  that  the  current  cannot  flow  through 
the  anodes  into  the  bath.  In  such  a  case,  the  further  increase 
of  the  content  of  potassium  cyanide  would  not  be  advisable, 
since  it  would  exceed  the  limit  admissible  for  a  dense  deposit  ; 
frequent  mechanical  cleaning  of  the  anodes  is  then  the  best 
remedy.  A  particularly  dense  slime  on  the  anodes  is  yielded 
by  baths  which  contain  small  quantities  of  conducting  salts, 
such,  for  instance,  as  are  prepared  from  the  double  and  triple 
salts.  By  giving  such  baths  additions  of  sulphites  or  chlorides 
a  less  compact  slime  is  formed  which  is  favorable  for  solution 
in  potassium  cyanide.  This  effect  is  without  doubt  due  to  the 
anions  of  the  conducting  salts  appearing  on  the  anodes. 

The  sluggish  formation  of  the  deposit,  however,  may  also  be 
due  to  a  want  of  metallic  salts.  In  this  case  not  only  potassium 
cyanide,  but  also  solution  of  copper  cyanide  and  zinc  cyanide 
in  potassium  cyanide,  has  to  be  added.  For  this  purpose  pre- 
pare a  concentrated  solution  of  potassium  cyanide  in  water, 
and  a  solution  of  equal  parts  of  blue  vitriol  and  zinc  sulphate 
in  water.  From  the  latter,  precipitate  the  copper  and  zinc  as 
carbonates  with  a  solution  of  carbonate  of  soda  as  given  in 
formula  I.  After  allowing  the 'precipitate  to  settle,  pour  off 
the  clear  supernatant  fluid,  and  add  to  the  precipitate,  stirring 
vigorously,  of  the  potassium  cyanide  solution  until  it  is  dis- 
solved ;  if  heating  takes  place  thereby,  add  from  time  to  time 
a  little  cold  water.  Add  this  solution  with  a  small  excess  of 
potassium  cyanide,  and  the  addition  of  carbonate  or  bisulphite 
of  soda,  to  the  bath,  and  boil  the  latter  or  work  it  through 
with  the  current.  A  more  simple  method  is  to  procure  cop- 
per cyanide  and  zinc  cyanide,  or  concentrated  solutions  of 
these  combinations,  from  a  dealer  in  such  articles.  In  the 
first  case,  rub  in  a  mortar  equal  parts  of  zinc  cyanide  and 
copper  cyanide  with  water  to  a  thinly-fluid  paste.  Pour  this 
paste  into  a  potassium  cyanide  solution,  containing  about  7 
ozs.  of  potassium  cyanide  to  the  quart,  as  long  as  the  metallic 


358  ELECTRO-DEPOSITION    OF    METALS. 

cyanides  dissolve  quite  rapidly  by  stirring.  When  solution 
takes  place  but  slowly,  stop  the  addition  of  paste.  A  still 
more  simple  way  is  to  buy  crystallized  potassium-copper  cya- 
nide and  potassium-zinc  cyanide,  dissolve  these  salts  in  suit- 
able quantitative  proportions,  and  add  the  solution  to  the 
bath. 

When  a  brass  bath  contains  too  great  an  excess  of  potassium 
cyanide,  a  very  vigorous  evolution  of  gas  takes  place  on  the 
objects,  but  the  deposit  is  formed  slowly  or  not  at  all ;  besides? 
the  deposit  formed  has  a  tendency  to  peel  off  in  scratch-brush- 
ing. In  this  case  the  injurious  excess  has  to  be  removed, 
which  is  effected  by  pouring,  whilst  stirring  vigorously,  a 
quantity  of  the  above-mentioned  thinly-fluid  paste  of  zinc 
cyanide  and  of  copper  cyanide  into  the  bath.  The  addition 
of  metallic  cyanides  is  continued  only  so  long  as  they  dissolve 
with  rapidity,  so  as  not  to  fix  all  the  free  potassium  cyanide 
of  the  bath. 

When  a  brass  bath  has  not  been  used  for  some  time  a  white 
film  frequently  forms  on  its  surface.  This  is  best  removed  by 
pushing  it  by  means  of  a  piece  of  twisted  paper  into  one  corner 
of  the  bath,  and  lifting  it  off  with  a  shallow  dish.  It  may 
then  be  dissolved,  eventually  by  heating,  in  a  small  quantity 
of  potassium  cyanide  and  the  solution  added  to  the  bath. 

To  avoid  unnecessary  repetition  we  refer,  as  regards  the 
production  of  thick  deposits,  scratch-brushing  and  polishing 
of  the  plated  articles,  to  what  has  been  said  under  "  Execution 
of  Coppering,"  the  directions  given  there  being  also  valid  for 
brassing. 

The  deposition  of  several  metals  from  a  common  solution  is 
not  an  easy  task,  and  requires  attention  and  experience.  If, 
however,  the  directions  given  in  this  chapter  are  followed,  the 
operator  will  be  able  to  conduct,  after  short  experience,  the 
brassing  process  with  the  same  success  as  one  in  which  but  one 
metal  is  deposited. 

Special  attention  must  be  paid  to  frequent  thorough  mixing 
of  the  contents  of  the  bath,  so  that  the  fluids  are  renewed  on 


DEPOSITION    OF    COPPER,  BRASS    AND    BRONZE.  359 

the  cathodes,  because  otherwise,  by  reason  of  the  fluid  becom- 
ing poor  in  metal,  the  deposit  would  show  different  composi- 
tions, and  consequently  other  colors. 

For  the  production  of  deposits  of  brass  which  are  to  show  a 
tone  resembling  gold,  it  has  been  recommended  to  add  to  the 
brass  bath  an  aluminium  salt,  such  as  aluminium  chloride, 
•aluminium  sulphate,  etc.  Such  baths  have  been  offered  to  lay- 
men as  aluminium-bronze  baths,  with  the  assurance  that  the 
•deposit  obtained  from  them  consists  of  an  alloy  of  aluminium 
and  brass,  and  possesses  the  same  power  of  resisting  atmospheric 
influences  as  aluminium-bronze.  Although  these  commenda- 
tions are  evidently  misleading,  because,  notwithstanding,  in- 
numerable receipts  for  the  production  of  electro-deposits  of 
aluminium,  the  reduction  of  this  metal  from  solutions  of  its 
salts  has  thus  far  not  been  successfully  accomplished.  De- 
posits produced  in  such  brass  baths,  compounded  with  alu- 
minium salts,  were  subjected  to  examination,  and  in  no  case 
was  it  possible  to  establish  even  the  slightest  trace  of  alu- 
minium in  the  deposit.  However,  notwithstanding  that  a 
reduction  of  aluminium  does  not  take  place,  the  influence  of 
an  addition  of  an  aluminium  salt  to  brass  baths,  as  regards 
the  result  of  the  brass  tone,  cannot  be  denied,  but  up  to  the 
present  time  it  has  been  impossible  to  find  an  explanation  of 
this  fact.  If  a  brass  bath,  prepared  according  to  the  formulas 
given  above,  be  compounded  with  35  to  40  grains  of  alu- 
minium chloride  per  quart  of  bath,  the  resulting  deposit 
shows  a  warmer,  more  sad  brass  tone  than  that  yielded  by  a 
bath  without  such  an  addition,  and  if  the  bath  is  somewhat 
rich  in  copper,  the  color  of  the  deposit  almost  resembles  red 
gold.  However,  greater  power  of  resisting  atmospheric  influ- 
ence could  not  be  noticed,  neither  can  such  be  expected,  since 
the  deposit  consists  solely  of  zinc  and  copper. 

It  remains  to  be  mentioned  that  in  brassing,  the  distance  of 
the  objects  to  be  plated  from  the  anodes  is  of  considerable 
importance.  If  objects  with  deep  depressions"  or  high  reliefs 
are  suspended  in  the  brass  bath,  it  will  be  found  that,  with  the 


360  ELECTRO-DEPOSITION    OF    METALS. 

customary  distance  of  3|  to  5}  inches  from  the  anodes,  the 
brassing  of  the  portions  in  relief  nearest  to  the  anodes  will  turn 
out  a  lighter  color  than  that  of  the  depressed  portions,  which 
will  show  a  redder  deposit,  the  reason  for  this  being  that  the 
current  acts  more  strongly  upon  the  portions  in  relief,  and  con- 
sequently deposits  more  zinc  than  the  weaker  current  which 
strikes  the  depressions.  To  equalize  this  difference  the  objects 
have  to  be  correspondingly  further  removed  from  the  anodes, 
with  lamp-feet  up  to  9|  inches,  and  even  more,  when  a  deposit 
of  the  same  color  will  be  everywhere  formed. 

The  brassing  of  unground  iron  castings  is  especially  trouble- 
some, and  in  order  to  obtain  a  beautiful  and  clean  deposit  the 
preliminary  scratch-brushing  has  to  be  executed  with  special 
care;  but  even  then  the  color  of  the  brass  deposit  will  some- 
times be  found  to  possess  a  disagreeable  gray  tone.  This  is 
very  likely  largely  due  to  the  quality  of  the  iron  itself,  and  it 
is  advisable  first  to  give  the  casting  a  thin  coat  of  nickel  or 
or  tin,  upon  which  a  deposit  of  brass  of  the  usual  brilliancy 
can  be  produced.  In  baths  serving  for  brassing  iron  articles, 
a  large  excess  of  potassium  cyanide  must  be  avoided.  It  is, 
however,  an  advantage  to  increase  the  content  of  carbonate  of 
soda. 

Inlaying  of  brassed  objects  with  black  is  done  in-  the  same 
manner  as  described  under  "  Deposition  of  Copper." 

Brassing  by  contact  will  be  referred  to  in  the  chapter  "  Depo- 
sitions by  Contact." 

For  oxidizing,  patinizing  and  coloring  of  brass,  see  special 
chapter. 

Examination  of  brass  paths.  The  characteristic  indications 
by  which  a  deficiency,  and  too  large  an  excess  of  potassium 
cyanide  in  the  bath,  as  well  as  an  insufficient  content  of  metal, 
may  be  recognized,  have  already  been  discussed,  and  it  is  here 
only  necessary  to  refer  to  the  quantitative  determination  of  the 
separate  constituents. 

Free  potassium*  cyanide  and  the  content  of  copper  are  deter- 
jtnined  in  the  same  manner  as  described  under  copper  baths 


DEPOSITION    OF    COPPER,  BRASS    AND    BRONZE.  361i 

containing  potassium  cyanide.     Hence  only  the  determination 
of  zinc  has  here  to  be  considered.     For  making  this  deter- 
mination it  is  necessary  to  destroy  the  cyanide  combinations,, 
and  entirely  to  remove  the  copper.     For  this  purpose  bring  by 
means  of  the  pipette  10  cubic  centimeters  of  the  brass  bath; 
into  a  porcelain  dish,  and  proceed  in  the  same  manner  as  given. 
on   page  345  for  the  determination  of  copper  by  electrolysis. 
Dissolve  the  evaporated  residue  in  the  dish  in  water,  adding 
a  few  drops  of  pure  hydrochloric  acid.     Then  bring  the  solu- 
tion into  a  capacious  beaker,  dilute  with  water  to  about  250 
cubic  centimeters,  and  heat  to  boiling.     Now  add   about  10- 
cubic  centimeters  of  pure  dilute  sulphuric  acid   (1  :  10)  and 
stirring  constantly,  mix  with  a  solution  of  2.5  grammes  of 
crystallized  sodium.     Copper  sulphide  is  separated  while  the 
sulphurous  acid  escapes.     Cover  the  beaker  with  a  watch-glass, 
let  it  stand  for  15  minutes,  and  then  filter  off  the  precipitate. 
Wash  the  filter  thoroughly  with  sulphuretted  hydrogen  water,, 
and   evaporate  the  filtrate  together  with  the  wash  waters  to 
about  100  to  150  cubic  centimeters.     The  solution  contains  all. 
the  zinc,  and  can  be  at  once  titrated  (see  below). 

For  the  determination  of  zinc  by  electrolysis,  heat  the  solu- 
tion to  boiling,  mix  it  with  solution  of  sodium  carbonate  in 
excess,  and  after  the  precipitate  of  basic  zinc  carbonate  has 
settled,  filter  it  off.  Dissolve  the  precipitate  in  the  filter  with 
pure  dilute  sulphuric  acid,  bring  the  filtrate,  together  with  the 
waters  used  for  thoroughly  washing  the  filter,  into  a  clean, 
beaker,  and  neutralize  accurately  with  sodium  carbonate. 

Now  bring  into  the  platinum  dish,  previously  coppered,  5. 
grammes  of  potassium  oxalate  and  2  grammes  of  potassium 
sulphate  dissolved  in  a  small  quantity  of  water,  fill  the  plati- 
num dish  up  to  within  1  centimeter  from  the  rim  with  distilled 
water,  and  electrolyze  with  a  current-density  of  ND  100  =  0.5 
ampere.    The  dull,  bluish-white  deposit  of  zinc  is  treated  with 
water,  then   with  alcohol  and   ether,  dried   in  the  exsiccator 
over  sulphuric  acid  and  weighed.     The  determined  weight  oF 
the  zinc  deposit  multiplied  by  100  gives  the  content  of  zinc  in 
grammes  per  liter  of  brass  bath. 


362  ELECTRO-DEPOSITION    OF    METALS. 

For  the  volumetric  determination  of  the  zinc,  about  100  to  150 
cubic  centimeters  of  the  zinc  solution  resulting  after  the  pre- 
cipitation of  the  copper  are  used.  The  determination  is  based 
upon  the  principle  that  potassium  ferrocyanide  solution  pre- 
cipitates the  zinc  from  the  solution,  and  that  complete  precip- 
itation is  indicated  by  an  excess  of  potassium  ferrocyanide, 
yielding  a  brown  coloration  with  uranium  acetate.  If  now  the 
content  of  the  potassium  ferrocyanide  solution  is  known,  the 
•quantity  of  it  used  gives  the  content  of  zinc.  It  is  best  to  use 
a  solution  which  contains  per  liter  32.45  grammes  of  pure 
crystallized  potassium  ferrocyanide,  every  cubic  centimeter  of 
this  solution  corresponding  to  0.01  gramme  of  zinc.  Add, 
; stirring  constantly,  from  a  burette  potassium  ferrocyanide 
solution  to  the  zinc  solution  in  a  beaker  until  a  drop  of  the 
fluid  brought  upon  a  strip  of  filtering  paper  previously  satu- 
rated with  uranium  acetate  solution  and  again  dried  just 
shows  the  commencement  of  a  brown  coloration. 

Since  10  cubic  centimeters  of  the  brass  bath  were  used  for 
the  determination,  the  number  of  cubic  centimeters  of  potas- 
sium ferrocyanide  solution  consumed  gives  the  quantity  of 
zinc  in  grammes  per  liter  of  brass  bath.  Suppose  6  cubic 
centimeters  of  solution  have  been  consumed,  they  would  cor- 
respond to  0.06  gramme  zinc  (0.01  X  6).  Hence  since  in  10 
cubic  centimeters  of  bath  0.06  gramme  of  zinc  is  present,  the 
bath  contains  6  grammes  (0.06  X  100)  of  zinc  per  liter. 

If  thus  a  deficiency  of  zinc  in  the  bath,  due  to  long-continued 
working,  has  been  determined  the  initial  content  can  be  readily 
restored  by  the  addition  of  pure  potassium  zinc  cyanide.  The 
latter  contains  26  per  cent,  of  zinc,  and  the  quantity  required 
to  be  added  is  determined  in  the  same  manner  as  with  a  copper 
bath  (see  p.  348). 

Deposits  of  tombac,  i.  e.,  deposits  having  the  color  of  tombac, 
are  obtained  by  increasing  the  content  of  copper  in  the  brass 
baths. 

The  following  formula  gives  a  tombac  bath  which  works 
well : 


DEPOSITION    OF    COPPER,  BRASS    AND    BRONZE.  363 

Crystallized  potassium  copper  cyanide  7  ozs.,  crystallized 
potassium-zinc  cyanide  3J  ozs.,  crystallized  neutral  bisulphite 
of  soda  8}  ozs.,  potassium  cyanide  f  oz.,  water  10  quarts. 

Electro-motive  force  at  10  cm.  electrode  distance,  3  volts. 

Current-density,  0.3  ampere. 

It  is  of  special  advantage  for  the  deposition  of  tombac  to 
heat  the  bath  to  between  86°  and  95°  F.,  the  resulting  de- 
posits being  of  a  more  uniform  color  than  at  the  ordinary 
temperature. 

For  tombac  deposits  the  transferring  solution,  according  to 
Hess  (see  "  Deposition  of  Brass,"  Formula  V),  may  also  be 
employed,  tombac  sheets  being  used  as  anodes. 

Deposits  of  bronze.  Plating  of  metallic  objects  with  bronze, 
i.  e.,  a  copper-tin  alloy,  or  an  alloy  of  copper,  tin  and  zinc,  is 
but  seldom  practiced,  the  bronze  tone  being  in  most  cases 
imitated  by  a  brass  deposit  with  a  somewhat  larger  content  of 
-copper. 

For  coating  wrougJit  and  cast-iron  with  bronze,  Gountier 
recommends  the  following  solution  : 

Yellow  prussiate  of  potash  10 J-  ozs.,  cuprous  chloride  5£ 
ozs.,  stannous  chloride  (tin  salt)  14  ozs.,  sodium  hyposulphite 
14  ozs.,  water  10  quarts. 

According  to  Ruolz.  a  bronze  bath  is  prepared  as  follows : 
Dissolve  at  122°  to  140°  P.,  copper  cyanide  2.11  ozs.,  and 
oxide  of  tin  0.7  ozs.,  in  10  quarts  of  potassium  cyanide  solu- 
tion of  4°  Be.  The  solution  is  to  be  filtered. 

Eisner  prepares  a  bronze  bath  by  dissolving  21  ozs.  of  blue 
vitriol  in  10  quarts  of  water,  and  adding  a  solution  of  2J  ozs. 
of  chloride  of  tin  in  potash  lye. 

Salzede  recommends  the  following  bath,  which  is  to  be 
used  at  between  86°  and  95°  F.  :  Potassium  cyanide  3J  ozs., 
carbonate  of  potash  35J  ozs.,  stannous  chloride  (tin  salt)  0.42 
oz.,  cuprous  chloride  J  oz.,  water  10  quarts. 

Weiil  and  Newton  claim  to  obtain  beautiful  bronze  deposits 
from  solutions  of  the  double  tartrate  of  copper  and  potash  and 
the  double  tartrate  of  the  protoxide  of  tin  and  potash,  with 
caustic  potash,  but  fail  to  state  the  proportions. 


364  ELECTRO-DEPOSITION    OF    METALS. 

The  above  formulae  are  here  given  with  all  reserve,  since 
experiments  with  them  failed  to  give  satisfactory  results. 
With  Gountier's,  Ruolz's  and  Eisner's  baths  no  deposit  was 
obtained,  but  only  a  strong  evolution  of  hydrogen,  while  even 
with  a  strong  current,  Salzede's  bath  did  not  yield  a  bronze 
deposit,  but  simply  one  of  tin. 

The  following  method  of  preparing  a  bronze  bath  may  be 
recommended:  Prepare,  each  by  itself,  solutions  of  phosphate 
of  copper  and  stannous  chloride  (tin  salt)  in  sodium  pyropbos- 
phate.  From  a  blue  vitriol  solution  precipitate,  with  sodium 
phosphate,  phosphate  of  copper,  allow  the  latter  to  settle,  and 
after  pouring  off  the  clear  supernatant  fluid,  bring  it  to  solu- 
tion by  concentrated  solution  of  sodium  pyrophosphate.  On 
the  other  hand,  add  to  a  saturated  solution  of  sodium  pyro- 
phosphate, solution  of  tin  salt,  as  long  as  the  milky  precipi- 
tate formed  dissolves.  Of  these  two  metallic  solutions,  add  to 
a  solution  of  sodium  pyrophosphate,  which  contains  about  If 
ozs.  of  the  salt  to  the  quart,  until  the  precipitate  appears- 
quickly  and  of  the  desired  color.  For  anodes,  use  cast  bronze- 
plates,  which  dissolve  well  in  the  bath.  Some  sodium  phos- 
phate has  from  time  to  time  to  be  added  to  the  bath,  and  if 
the  color  becomes  too  light,  solution  of  copper,  and  if  too* 
dark,  solution  of  tin. 

For  nickel-bronze,  see  p.  315. 


CHAPTER  VII. 

DEPOSITION    OF    SILVER. 

Silver  (Ag  — 107.88  parts  by  weight)  and  its  properties. — 
Pure  silver  is  the  whitest  of  all  known  metals.  It  takes  a  fine 
polish,  is  softer  and  less  tenacious  than  copper,  but  harder  and 
more  tenacious  than  gold.  It  is  very  malleable  and  ductile, 
and  can  be  made  into  exceedingly  thin  leaves  and  fine  wire. 
Its  specific  gravity  is  10.48  to  10.55,  according  to  whether  it  is 
<jast  or  hammered.  It  melts  at  about  1832°  F.  It  is  unacted 
upon  by  the  air,  but  in  the  atmosphere  of  towns  it  gradually 
becomes  coated  with  a  film  of  silver  sulphide.  It  is  rapidly 
dissolved  by  nitric  acid,  nitrogen  dioxide  being  evolved. 
Hydrochloric  acid  has  bub  little  action  upon  it  even  at  a  boil- 
ing heat ;  when  heated  with  concentrated  sulphuric  acid  it 
yields  sulphur  dioxide  and  silver  sulphate. 

Chlorine  acts  upon  silver  at  the  ordinary  temperature. 
Silver  has  great  affinity  for  sulphur,  and  readily  fuses  with  it 
to  silver  sulphide.  Sulphuretted  hydrogen  blackens  silver, 
brown-black  silver  sulphide  being  formed  (tarnishing  of  silver 
in  rooms  in  which  gas  is  burned).  Such  tarnishing  is  most 
readily  removed  by  potassium  cyanide  solution. 

Concentrated  sulphuric  acid  combines  at  a  boiling  point  with 
•silver  to  silver  sulphate,  sulphurous  acid  escaping.  Nitric  acid 
readily  dissolves  silver  at  a  gentle  heat,  and  at  a  higher  tem- 
perature with  considerable  violence,  silver  nitrate  (lunar  caus- 
tic) being  formed,  while  nitrogen  dioxide  escapes.  Watery 
chromic  acid  converts  silver  into  red  silver  chromate,  and  this 
conversion  is  made  use  of  as  a  test  for  silvering.  By  touch- 
ing silver  or  genuine  silver-plating  with  a  drop  of  a  solution 
•obtained  by  dissolving  potassium  dichromate  in  nitric  acid  of 
1.2  specific  gravity,  a  red  stain  is  formed. 

(365) 


366  ELECTRO-DEPOSITION    OF    METALS. 

Electro-plating  with  silver  was,  of  all  electro-metallurgical 
processes,  the  first  which  was  carried  on  on  a  large  scale  and 
has  reached  enormous  proportions.  Large  quantities  of  silver 
are  annually  consumed  for  this  purpose,  and  it  is  to  be  re- 
gretted that  no  accurate  statistics  regarding  this  consumption 
are  available. 

Silver  baths.  The  longer  an  electro-plating  process  has  been 
carried  on,  the  greater,  as  a  rule,  the  number  of  existing  for- 
mulae for  baths  will  be;  but  silver  baths  are  an  exception  to  this 
rule.  If  it  is  taken  into  consideration  that  silver-plating  has 
been  practically  carried  on  for  more  than  seventy  years,  the 
number  of  formula?  might  be  expected  to  be  at  least  equal  to 
those  for  nickel-plating,  which  is  of  much  more  recent  origin. 
Such,  however,  is  not  the  case,  and  chiefly  for  the  reason  that 
the  attempts  to  improve  the  silver  baths,  which  were  made 
either  with  a  view  to  banish  the  poisonous  potassium  cyanide 
from  the  silver-plating  industry,  or  otherwise  to  advance  the 
plating  process,  could  absolutely  show  no  better  results  than 
the  baths  used  by  the  first  silver-platers.  However,  that 
attempts  to  make  such  improvements  have  not  been  entirely 
abandoned  is  shown  by  Zinin's  proposition  to  substitute  solu- 
tion of  silver  iodide  in  potassium  iodide  for  a  solution  contain- 
ing potassium  cyanide,  or  by  Jordis'  proposition  to  use  silver 
lactate  baths.  While  the  bath  according  to  Ziniri  yields  bad 
results  as  compared  with  the  old  baths  containing  potassium 
cyanide,  quite  good  silvering  is  obtained  with  a  bath  accord- 
ing to  Jordis,  but  independent  of  the  fact  that  the  bath  con- 
tains no  potassium  cyanide,  no  special  advantages  could  be 
established.  Hence  there  is  no  good  reason  for  including 
other  directions  for  silver  baths  in  this  work,  which  is  pri- 
marily intended  for  practical  use,  and  only  formulae  for  the 
most  approved  baths  will  be  given. 

However,  before  describing  the  preparation  of  the  baths,  a 
few  words  may  be  said  in  regard  to  the  old  dispute,  whether  it 
is  preferable  to  use  silver  cyanide  or  silver  chloride.  Without 
touching  upon  all  the  arguments  advanced,  it  may  be  asserted, 


DEPOSITION    OF    SILVER.  367 

by  reason  of  conscientious  comparative  experiments,  that  the 
results  are  the  same,  and  that  the  life  of  the  bath  is  also  the 
same,  whether  one  or  the  other  salt  has  been  used  in  its 
orginal  preparation.  From  the  chemical  view-point,  pre- 
ference had  to  be  given  to  silver  cyanide,  but  in  practice,, 
baths  prepared  with  silver  chloride  were  found  to  possess 
certain  advantages,  and  theory  has  furnished  an  explanation 
of  them. 

One  of  these  advantages  is  found  in  the  fact  that  by  reason 
of  the  potassium  chloride  formed,  the  resistance  of  a  bath 
prepared  with  silver  chloride  is  considerably  less  than  that  of 
a  silver  cyanide  bath,  and,  with  the  same  current-density,  the 
latter,  therefore,  requires  a  greater  electro-motive  force. 

Theoretically,  preference  has  further  to  be  given  to  silver 
chloride,  because  a  portion  of  the  potassium  chloride  formed 
is  dissociated,  and  potassium-ions  and  chlorine-ions  thus  get 
into  the  solution.  These  potassium-ions  augment  the  potas- 
sium-ions which  are  present  as  a  result  of  the  dissociation  of 
the  potassium  cyanide  and  silver  cyanide  and  thus  increase 
the  efficiency.  On  the  other  hand,  in  addition  to  cyanogen- 
ions,  chlorine-ions  are  separated  on  the  anodes  and  augment 
the  supply  of  silver-ions  in  the  electrolytes.  Furthermore,  the 
presence  of  potassium  chloride  facilitates  the  conversion  of  the 
silver  cyanide  formed  on  the  anodes  into  potassium  silver 
cyanide,  according  to  the  following  equation  : 

2AgCy       +       KC1  KAgCya       +      AgCl 

Silver  cyanide.     Potassium  chloride.     Potassium  silver        Silver  chloride. 

cyanide. 

While,  according  to  this,  preference  may  be  given  to  silver 
chloride  for  the  preparation  of  silver  baths,  and  the  more  so  as 
it  is  more  easily  prepared  than  silver  cyanide,  yet  for  refresh- 
ing the  baths,  which  becomes  from  time  to  time  necessary  to 
increase  their  content  of  silver,  recourse  must  be  had  to  silver 
cyanide,  because  with  the  use  of  silver  chloride  for  this  pur- 
pose, the  baths  would  become  thick  in  consequence  of  a  con- 


-368       •  ELECTRO-DEPOSITION    OP    METALS. 

slant  supply  of  further  quantities  of  potassium  chloride,  and 
•the  silver  separate  with  a  coarse  structure. 

Silver-bath  for  a  heavy  deposit  of  silver  (silvering  by  weight). 

I.  98  to  99  per  cent,  potassium  cyanide  14  ozs.,  fine  silver 
-as  silver  chloride  Sf  ozs.,  distilled  water  10  quarts. 

Electro-motive  force  a,t  10  cm.  electrode-distance,  0.75  volt. 

Current  density,  0.3  ampere. 

la.  98  to^99  per  cent,  potassium  cyanide  8f  ozs.,  fine  silver 
-as  silver  cyanide  8}  ozs.,  distilled  water  10  quarts. 

Electro-motive  force  at  10  cm.  electrode-distance,  1  volt. 

Current  density,  0.3  ampere. 

Preparation  of  bath  L  with  silver  chloride.  Dissolve  14  ozs. 
•of  chemically  pure  nitrate  of  silver,  best  the  crystallized,  and 
not  the  fused  article,  in  5  quarts  of  water,  and  add  to  the 
solution  pure  hydrochloric  acid,  or  common  salt  solution,  with 
vigorous  stirring  or  shaking,  until  a  sample  of  the  fluid  filtered 
through  a  paper  filter  forms  no  longer  a  white  caseous  pre- 
cipitate of  silver  chloride  when  compounded  with  a  drop  of 
hydrochloric  acid.  These,  as  well  as  the  succeeding  opera- 
tions, until  the  silver  chloride  is  ready,  have  to  be  performed 
in  a  darkened  room,  as  silver  chloride  is  partially  decomposed 
by  light.  Now  separate  the  precipitate  of  silver  chloride  from 
the  solution  by  filtering,  using  best  a  large  bag  of  close  felt, 
-and  wash  the  precipitate  in  the  felt  bag  with  fresh  water. 
•Continue  the  washing  until  blue  litmus  paper  is  no  longer 
reddened  by  the  wash-water,  if  hydrochloric  acid  was  used 
for  precipitating,  or,  if  common  salt  solution  was  used,  until 
-a  small  quantity  of  the  wash-water,  on  being  mixed  with  a 
drop  of  lunar  caustic  solution,  produces  only  a  slight  milky 
turbidity  and  no  precipitate.  Now  bring  the  washed  silver 
-chloride  in  portions  from  the  felt  bag  into  a  porcelain  mortar, 
rub  it  with  water  to  a  thin  paste,  and  pour  the  latter  into  the 
potassium  cyanide  solution  consisting  of  14  ozs.  of  98  per 
•cent,  potassium  cyanide  in  5  quarts  of  water,  in  which,  by 
vigorous  stirring,  the  silver  chloride  gradually  dissolves.  All 
the  precipitated  silver  chloride  having  been  brought  into 


DEPOSITION    OF    SILVER.  369 

solution,  dilute  with  water  to  10  quarts  of  fluid,  and  boil  the 
bath,  if  possible,  for  an  hour,  replacing  the  water  lost  by 
evaporation.  A  small  quantity  of  black  sediment  containing 
.silver  thereby  separates,  from  which  the  colorless  fluid  is 
filtered  off.  This  sediment  is  added  to  the  silver  residues, 
-and  is  worked  together  with  them  for  the  recovery  of  the 
silver  by  one  of  the  methods  to  be  described  later  on. 

Preparation  of  bath  la  with  silver  cyanide.  Dissolve  14 
ounces  of  chemically  pure  crystallized  nitrate  of  silver  in  5 
quarts  of  water,  and  precipitate  the  silver  with  prussic  acid, 
adding  the  latter  until  no  more  precipitate  is  produced  by  the 
addition  of  a  few  drops  of  prussic  acid  to  a  filtered  sample  of 
the  fluid.  Now  filter,  wash,  and  proceed  for  the  rest  exactly 
as  stated  for  the  bath  with  silver  chloride,  except  that  only  8f 
ounces  of  potassium  cyanide  are  taken  for  dissolving  the  silver 
cyanide.  In  working  with  prussic  acid  avoid  inhaling  the 
vapor  which  escapes  from  the  liquid  prussic  acid,  especially 
in  the  warm  season  of  the  year ;  and  be  careful  the  acid  does 
not  come  in  contact  with  cuts  on  the  hands.  It  is  one  of  the 
most  rapidly  acting  poisons. 

Silver  cyanide  may  also  be  prepared  as  follows  :  Dissolve 
14  ounces  of  chemically  pure  crystallized  nitrate  of  silver  in  5 
quarts  of  water,  and  add  moderately  concentrated  potassium 
cyanide  solution  until  no  more  precipitate  is  formed,  avoid- 
ing, however,  an  excess  of  the  precipitating  agent,  as  it  would 
again  dissolve  a  portion  of  the  silver  cyanide.  The  precipi- 
tated silver  cyanide  is  filtered  off,  washed  and  dissolved  in 
potassium  cyanide,  as  above  described. 

The  preparation  of  the  silver  bath  according  to  the  above 
formulae  is  more  conveniently  effected  by  using  pure  crystal- 
lized potassium-silver  nitrate  in  the  following  proportions : 

16.  98-per  cent,  potassium  cyanide,  6J  to  7  ozs.  ;  crystal- 
lized potassium-silver  cyanide.  17J  ozs.  ;  distilled  water,  10 
quarts. 

Electro-motive  force  and  current-density  as.  for  la. 

The  salts  are  simply  dissolved  in  the  cold  water. 
24 


370  ELECTRO-DEPOSITION    OF    METALS. 

The  baths  prepared  according  to  formulae  I,  la  or  Ib  serve 
chiefly  for  the  production  of  a  heavy  deposit  upon  German 
silver  articles,  especially  table  and  other  household  utensils. 
Of  course,  they  may  also  be  used  for  plating  other  metals  by 
weight. 

Silver  bath  for  ordinary  electro-silvering.  II.  98-per  cent, 
potassium  cyanide,  6|  to  7  ounces ;  fine  silver  (as  silver 
nitrate  or  chloride),  3|  ounces ;  distilled  water,  10  quarts. 

Electro-motive  force,  for  silver  chloride,  at  10  cm.  electrode- 
distance,  1.25  volts. 

Current-density,  0.3  ampere. 

To  prepare  the  bath  dissolve  5J  ounces  of  chemically  pure- 
crystallized  nitrate  of  silver  in  5  quarts  of  distilled  water  ;  in 
the  other  5  quarts  of  water  dissolve  the  potassium  cyanide,  and 
mix  both  solutions.  Or  if  chloride  of  silver  is  to  be  used,  pre- 
cipitate the  solution  of  3J  ounces  of  the  silver  salt  in  the  same 
manner  as  given  for  formula  I ;  wash  the  precipitated  chloride 
of  silver,  and  dissolve  it  in  the  potassium  cyanide  solution. 

Ila.  98-per  cent,  potassium  cyanide  If  ozs.,  crystallized 
potassium-silver  cyanide  7  ozs,,  distilled  water  10  quarts. 

Dissolve  the  salts  in  the  cold  water. 

For  the  preparation  of  silver  baths  double  and  triple  silver 
salts  are  brought  into  commerce  by  some  manufacturers. 

Such  salts  require  simply  dissolving  in  water.  However, 
they  offer  no  special  advantages,  since  the  preparation  of  baths 
according  to  formulas  Ib  and  Ila  can  scarcely  be  surpassed  as 
regards  simplicity. 

Tanks  for  silver  baths.  As  receptacles  for  silver  baths,  tanks 
of  stoneware  and  enameled  iron  tanks,  as  well  as  wood  tanks 
lead-lined  and  coated  or  lined  with  celluloid  can  only  be  used. 

Treatment  of  the  silver  baths. — Silver  anodes.  Frequently  the 
error  is  committed  of  adding  too  much  potassium  cyanide 
to  the  bath.  A  certain  excess  of  it  must  be  present,  and  in 
the  formulas  given,  this  has  been  taken  into  consideration. 
For  dissolving  the  silver  cyanide  prepared  from  14  ounces  of 
nitrate  of  silver,  as  given  in  formula  la,  only  about  5J  ounces 


DEPOSITION    OP    SILVER.  371 

of  potassium  cyanide  are  required,  and  the  consequence  of 
working  with  such  a  bath,  devoid  of  all  excess,  would  be  that, 
on  the  one  hand,  the  bath  would  offer  considerable  resistance 
to  the  current,  and,  on  the  other,  that  the  deposit  would  not 
be  uniform  and  homogeneous,  and  the  anodes  would  be  coated 
with  silver  cyanide.  Hence,  with  the  use  of  a  normal  current, 
about  0.35  to  0.42  oz.  more  of  potassium  cyanide  is  added 
per  quart  of  bath.  However,  when  working  with  a  stronger 
current,  this  excess  would  already  be  too  large,  and  the 
deposit  would  not  adhere  properly,  and  rise  up  in  scratch- 
brushing.  And,  again,  with  a  very  weak  current,  the  baths 
can  without  disadvantage  stand  a  larger  excess.  As  a  rule, 
however,  the  proportions  between  fine  silver  and  potassium 
cyanide  given  in  the  above  formulas  may  be  considered  as 
normal,  and  with  the  current-densities  prescribed,  a  deposit 
of  fine  structure,  which  adheres  firmly,  will  result. 

By  reason  of  the  slight  electro-motive  force  required  for 
silvering,  in  plating  larger  object-surfaces  the  cells  are  not 
coupled  one  after  the  other  for  electro-motive  force,  but  in 
parallel.  In  no  case  must  an  evolution  of  hydrogen  be  per- 
ceptible on  the  objects,  and  the  current  must  be  the  more 
weakened,  the  larger  the  excess  of  potassium  cyanide  in  the 
bath. 

In  the  silver  baths  prepared  according  to  the  formulas  given 
above,  the  excess  of  potassium  cyanide  amounts  to  0.35  to 
0.42  oz.  per  quart,  and  is  only  increased  in  silver  baths  which 
are  to  serve  for  the  direct  silvering  of  tin  and  of  alloys  with  a 
large  content  of  nickel,  as  will  be  shown  later  on.  Baths  for 
ordinary,  as  well  as  light,  silvering,  with  0.35  oz.  of  silver  per 
quart,  would  only  require  an  excess  of  0.17  oz.  of  potassium 
cyanide.  However,  since  the  larger  excess  of  0.35  oz.  is  no 
disadvantage,  and  allows  of  working  with  less  electro-motive 
force,  it  is  generally  preferred.  The  electro-motive  force  given 
for  the  separate  formulas  is  applicable  only  when  the  anode- 
surface  is  of  the  same  size,  or  approximately  so,  as  the  object- 
surface.  If,  for  reasons  of  economy,  the  work  is  carried  on 


372  ELECTRO-DEPOSITION    OF    METALS. 

with  considerably  smaller  anode-surfaces,  the  electro-motive 
force  has  to  be  adequately  increased  in  order  to  conduct  into 
the  bath  a  quantity  of  current  corresponding  to  the  normal 
current-density. 

Whether  too  much,  or  not  enough,  potassium  cyanide  is 
present  in  the  bath  is  indicated  by  the  appearance  of  the 
plated  objects  and  the  properties  of  the  deposit,  as  well  as  by 
the  behavior  of  the  anodes  in  the  bath  during  and  after  silver- 
ing. It  may  be  accepted,  as  a  rule,  that  with  a  moderate 
current  the  object  should,  in  the  course  of  10  to  15  minutes, 
be  coated  with  a  thin,  dead-white  film  of  silver.  If  this  be 
not  the  case,  and  the  film  of  silver  shows  a  meager  bluish- 
white  tone,  potassium  cyanide  is  wanting.  However,  if,  on 
the  other  hand,  the  dead-white  deposit  forms  within  2  or  3 
minutes,  and  shows  a  crystalline  structure,  or  a  dark  tone 
playing  into  gray-black,  the  content  of  potassium  cyanide  in 
the  bath  is  too  large,  provided  the  current  is  not  excessively 
strong.  If  copper  and  brass  become  coated  with  silver  with- 
out the  co-operation  of  the  current,  the  bath  contains  too 
much  potassium  cyanide. 

In  silver-plating,  even  if  the  objects  are  to  be  only  thinly 
coated,  insoluble  platinum  anodes-should  never  be  used,  but 
only  anodes  of  fine  silver,  which  are  capable  of  maintaining 
the  content  of  silver  in  the  bath  quite  constant.  From  the 
behavior  and  appearance  of  the  anodes,  a  conclusion  may  also 
be  drawn  as  to  whether  the  content  of  potassium  cyanide  in 
the  bath  is  too  large  or  too  small.  If  the  anodes  remain 
silver-white  during  plating,  it  is  a  sure  sign  that  the  bath 
contains  more  potassium  cyanide  than  is  necessary  and  de- 
sirable ;  but,  if  they  turn  gray  or  blackish,  and  retain  this 
color  after  plating,  when  no  current  is  introduced  into  the 
bath  for  a  quarter  of  an  hour  or  more,  potassium  cyanide  is 
wanting.  On  the  other  hand,  the  correct  content  of  potassium 
cyanide  is  present,  when  the  anodes  acquire  during  the  plat- 
ing process  a  gray  tone,  which,  after  the  interruption  of  the 
current,  gradually  changes  back  to  pure  white. 


DEPOSITION    OF    SILVER.  373 

The  use  of  steel  sheets  as  anodes  for  silver  baths  in  place  of 
silver  anodes,  as  has  been  proposed,  cannot  be  approved, 
especially  when  chloride  of  silver  has  been  used  for  the 
preparation  of  the  bath,  or  other  chlorides  are  present  in 
it.  The  chloride-ions  would  bring  iron  into  solution  and 
this  would  form  potassium-ferrocyanide  with  the  potassium 
cyanide. 

If  it  is  shown  by  the  process  of  silvering  itself,  or  by  the 
appearance  of  the  articles,  or  of  the  anodes,  that  potassium  cya- 
nide is  wanting  in  the  bath,  it  should  be  immediately  added, 
though  never  more  than  30  to  37J  grains  per  quart  of  bath  at 
one  time,  so  as  to  avoid  going  to  the  other  extreme.  Too  large 
a  content  of  potassium  cyanide  is  remedied  by  adding  to  the 
bath,  stirring  constantly,  a  small  quantity  of  cyanide  or  chlo- 
ride of  silver  rubbed  with  water  to  a  thinly-fluid  paste,  whereby 
the  excess  is  rendered  harmless  in  consequence  of  the  formation 
of  the  double  salt  of  silver  and  potassium  cyanide.  Instead  of 
such  addition,  the  current,  may,  however,  be  used  for  correct- 
ing the  excess.  For  this  purpose  suspend  as  many  silver 
anodes  as  possible  to  the  anode-rods,  but  only  a  single  anode 
as  an  object  to  the  object-rod,  and  allow  the  current  to  pass 
for  a  few  hours  through  the  bath,  whereby  the  excess  of 
potassium  cyanide  is  removed  or  rendered  harmless  by  the 
dissolving  silver. 

The  bath  can  be  kept  quite  constant  by  silver  anodes,  pro- 
vided potassium  cyanide  be  regularly  added  at  certain  inter- 
vals, and  the  anode-surface  is  equal  to  that  of  the  objects  to 
be  plated.  But  since,  on  account  of  the  expense,  a  relatively 
small  anode-surface  is  frequently  used,  the  content  of  silver  in 
a  bath  continuously  worked  will  finally  become  lower,  and 
augmentation,  by  the  addition  of  silver,  will  be  required.  The 
manner  of  effecting  this  augmentation  depends  on  whether  the 
baths  are  used  for  plating  by  weight  or  for  lighter  silvering,  or 
whether  the  baths  are  worked  without  stopping  from  morning 
till  evening.  For  replacing  the  deficiency  in  baths  prepared 
according  to  formula  I  and  la,  it  is  advisable  to  use  exclu- 


374  ELECTRO-DEPOSITION    OF    METALS. 

sively  solution  of  silver  cyanide  in  potassium  cyanide,  or  of 
crystallized  potassium-silver  cyanide  in  water. 

It  has  previously  been  mentioned  that  with  proper  treatment 
baths  made  with  chloride  of  silver  have  the  same  duration  of 
life  as  those  prepared  with  silver  cyanide.  The  chief  feature 
of  such  proper  treatment  is  not  to  use  chloride  of  silver  dis- 
solved in  potassium  cyanide  for  augmenting  the  content  of 
silver,  but  to  employ  silver  cyanide  instead,  since  by  the  use  of 
the  former,  the  bath  thickens  in  consequence  of  the  potassium 
chloride  which  is  simultaneously  introduced.  The  effect  of 
such  thickening  is  that  the  deposits  are  formed  less  homo- 
geneously and  with  coarser  structure. 

A  gradual  thickening  of  the  bath  may  also  take  place  if  po- 
tassium cyanide  containing  potash  is  used,  instead  of  the  prep- 
aration free  from  potash,  and  of  98  to  99  per  cent,  purity.  Even 
pure  fused  potassium  cyanide  produces  a  thickening  of  the 
bath,  which,  however,  progresses  very  slowly.  This  thicken- 
ing is  due  to  a  portion  of  the  excess  of  potassium  cyanide  being 
by  the  action  of  the  air  converted  into  potassium  carbonate, 
and  if  the  quantity  of  the  latter  exceeds  J  oz.  per  quart,  it  has 
to  be  neutralized.  For  this  purpose  prussic  acid  was  formerly 
used  in  order  to  effect  a  conversion  of  the  potassium  carbonate 
into  potassium  cyanide.  It  is,  however,  a  well-known  fact 
that  carbonic  acid  decomposes  the  potassium  cyanide,  potas- 
sium carbonate  and  prussic  acid  being  formed,  and  the  addi- 
tion of  prussic  acid  would  therefore  appear  not  very  suitable 
for  attaining  the  object  in  view. 

It  is  better  to  use  solutions  of  calcium  cyanide  or  barium 
cyanide,  and  add  them  so  long  as  a  precipitate  of  calcium  car- 
bonate or  barium  carbonate  is  formed.  The  solutions  should, 
however,  be  freshly  prepared.  The  precipitate  formed  is 
allowed  to  settle,  when  the  clear  solution  is  siphoned  off,  and 
the  residue  filtered  through  a  paper  filter. 

Since,  as  mentioned  above,  the  proportion  of  excess  of  potas- 
sium cyanide  to  the  content  of  silver  undergoes  changes  ac- 
cording to  the  proportion  of  the  object-surface  to  the  anode- 


DEPOSITION    OF    SILVER.  375 

•surface,  the  temperature  of  the  bath,  etc.,  it  becomes  necessary 
to  add  one  or  the  other  in  order  to  maintain  the  proper  pro- 
portions and  the  effective  working  of  the  bath. 

To  determine  rapidly  whether  the  bath  contains  silver  and 
-excess  of  potassium  cyanide  in  proper  proportions,  the  follow- 
ing methods  may  be  used:  Dissolve  1  gramme  (15.43  grains) 
of  chemically  pure  crystallized  nitrate  of  silver  in  20  grammes 
(0.7  oz.)  of  water  and  gradually  add  this  solution,  whilst  con- 
stantly stirring  with  a  glass  rod,  to  100  grammes  (3.52  ozs.) 
of  the  silver  bath  in  a  beaker,  so  long  as  the  precipitate  of 
silver  cyanide  formed  dissolves  by  itself.  If,  after  adding  the 
entire  quantity  of  silver  solution,  the  precipitate  dissolves  rap- 
idly, too  large  an  excess  of  potassium  cyanide  is  present  in  the 
bath  ;  and  vice  versa,  if  the  precipitate  does  not  completely 
dissolve,  after  stirring,  potassium  cyanide  is  wanting. 

The  quantitative  determination  of  the  content  of  potassium 
-cyanide  and  of  silver  will  be  described  later  on  under  "  Ex- 
amination of  Silver  Baths," 

Agitation  of  silver  baths.  In  heavy  silver-plating,  constant 
agitation  of  the  strata  of  fluid  is  of  decided  advantage,  grooves 
and  blooms  being  otherwise  readily  formed  upon  the  plated 
objects,  especially  when  the  baths  are  over-concentrated  or 
thickened.  The  depressed  grooves  can  only  be  explained  by 
the  fact  that  the  strata  of  fluid  on  the  cathodes  having  become 
specifically  lighter  by  yielding  metal  are  subject  to  a  current 
towards  the  surface ;  the  lower  strata  richer  in  silver  give  rise 
to  heavier  deposits  on  the  lower  cathode  portions,  so  that 
agitation  of  the  bath  becomes  an  actual  necessity. 

With  a  bath  in  constant  agitation  a  greater  current-density 
may  be  used,  the  deposits,  notwithstanding  the  greater  current- 
density,  forming  with  finer  structure  and  in  a  correspondingly 
shorter  time,  which  is  especially  noteworthy  for  heavy  silver- 
ing. To  keep  the  articles  in  gentle  motion  while  in  the  bath? 
•one  method  is  to  connect  the  suspending  rods  to  a  frame  of 
iron  having  four  wheels,  about  3  inches  in  diameter,  connected 
;to  it,  which  slowly  travel  to  and  fro  to  the  extent  of  3  or  4 


376 


ELECTRO-DEPOSITION    OF    METALS. 


inches  upon  inclined  rails  attached  to  the  upper  edge  of  the- 
tank,  the  motion,  which  is  both  horizontal  and  vertical,  being 
given  by  means  of  an  eccentric  wheel  driven  by  steam  power. 
By  another  arrangement,  the  frame  supporting  the  articles 
does  not  rest  upon  the  tank,  but  is  suspended  above  the  bath,, 
and  receives  a  slow  swinging  motion  from  a  small  eccentric  or 
its  equivalent.  In  the  Elkington  establishment  at  Birming- 
ham the  following  arrangement  is  in  use :  All  the  suspending 
rods  of  the  bath  rest  upon  a  copper  mounting,  which,  by  each 
revolution  of  an  eccentric  wheel,  is  lifted  about  £  inch,  and 
then  returned  to  its  position.  The  copper  mounting  is  con- 

FIG.  123. 


nected  to  the  main  negative  wire  of  the  dynamo-machine  by 
a  copper  cable.  The  same  object  may  also  be  attained  by  giv- 
ing the  articles  a  horizontal,  instead  of  a  vertical  motion,  as- 
shown  in  Fig.  123,  in  which  the  motion  is  produced  by  an 
eccentric  wheel  on  the  side. 

With  equal,  if  not  better,  success  the  mechanically  moved 
stirring  apparatus,  which  will  be  described  under  "  Copper 
Galvanoplasty,"  may  be  used.  In  this  apparatus  several  glass- 
rods  movable  around  a  pivot  keep  the  bath  in  constant  motion. 
Where  such  a  stirring  apparatus  cannot  be  conveniently 


DEPOSITION    OF    SILVER.  377 

arranged,  the  motion  of  the  bath  may  be  produced  by  intro- 
ducing, by  means  of  a  pump,  air  on  the  bottom  of  the  tank. 

A  singular  phenomenon  in  regard  to  silver  baths,  which 
has  not  yet  been  explained,  may  here  be  mentioned.  A  small 
addition  of  certain,  and  especially  of  organic,  substances, 
which,  however,  must  not  be  made  suddenly  or  in  too  large 
quantities,  produces  a  fuller  and  better  adhering  deposit  of 
greater  luster  than  can  be  produced  in  fresh  baths.  Elking- 
ton  observed  that  an  addition  of  a  few  drops  of  carbon  disul- 
phide  to  the  bath  made  the  silvering  more  lustrous,  while 
others  claim  to  have  used  with  success  solutions  of  iodine  in 
chloroform,  of  gutta-percha  in  chloroform,  as  well  as  heavy 
hydrocarbons,  tar,  oils,  etc. 

A  silver  bath,  as  shown  by  experience,  becomes  without 
doubt  better  in  the  degree  in  which  it  takes  up  small  quan- 
tities of  organic  substances  from  the  air  and  from  dust ;  but 
numerous  experiments  have  failed  to  confirm  Elkiugton'^ 
observation  that  the  formation  of  the  deposit  or  its  appearance 
is  essentially  influenced  by  the  addition  of  carbon  disulphide 
or  any  of  the  above-mentioned  solutions  of  organic  origin 
either  in  very  small  or  considerable  quantities.  Many  baths 
have  been  entirely  spoiled  by  an  attempt  to  change  them  into 
bright-working  baths  by  the  addition  of  such  ingredients,  and 
hence  it  is  best  to  leave  such  experiments  alone.  It  may, 
however,  be  stated  that  by  the  addition  of  a  few  drops  of  liquid 
ammonia,  fresh  silver  baths  accommodate  themselves  more 
rapidly  to  regular  performance. 

However,  the  use  of  carbon  disulphide  as  an  addition  to 
the  silver  bath  for  bright  plating  is  advocated  by  some  electro- 
platers,  and  some  preparations  for  this  purpose  may  here  be 
given.  The  carbon  disulphide  should  not  be  directly  added 
to  the  bath,  as  in  that  case  it  does  not  intimately  mix  with 
the  bath,  it  settling  on  the  bottom  of  the  vat  and  the  deposit 
would  turn  out  defective.  The  following  plan  has  been  highly 
recommended  for  the  ordinary  silver  bath  prepared  from  chlo- 
ride of  silver  and  potassium  cyanide  :  Add  to  1  quart  of  the- 


-378  ELECTRO-DEPOSITION    OF    METALS. 

.silver  bath  in  a  bottle  10  drops  of  carbon  disulpbide.  Cork 
the  bottle  tightly  and  vigorously  shake  from  time  to  time. 
.Allow  the  bottle  to  stand  over  night  for  the  fluid  to  settle,  and 
then  pour  off  the  supernatant  fluid.  A  residue  of  a  dark  color 
will  be  found  on  the  bottom  of  the  bottle.  The  fluid  thus 
obtained  should  be  perfectly  clear,  and  forms  the  carbon  disul- 
phide solution  to  be  added  to  the  actual  silver  bath. 

For  the  preparation  of  a  bath  for  bright-plating  add  about 
.J  oz.  of  the  carbon  disulphide  solution  to  every  45  quarts  of 
^he  silver  bath,  and  mix  thoroughly.  With  proper  treatment 
the  deposit  will  be  smooth  and  bright. 

If  the  deposit  does  not  show  the  desired  surface  but  is  still 
partly  mat  and  partly  white,  the  bath  does  not  contain  suffi- 
cient carbon  disulphide  solution  and  more  has  to  be  added  to 
obtain  satisfactory  results.  Since  the  carbon  disulphide  is 
consumed  in  plating,  carbon  disulphide  solution  has  of  course 
-to  be  added  from  time  to  time  to  the  silver  bath.  The  want 
of  carbon  disulphide  in  the  bath  is  readily  recognized  by  the 
appearance  of  the  deposit.  Care  must,  however,  be  exercised 
in  making  such  an  addition  since  too  much  of  it  has  an 
injurious  effect  upon  the  deposit.  The  deposit  thus  obtained 
is  smooth  and  has  a  slight  luster.  It  is  considerably  harder 
^than  a  mat  deposit  but  can  be  polished  without  trouble. 

Another  method  of  preparing  a  solution  for  bright-plating  is 
as  follows:  Put  1  quart  of  ordinary  silver-plating  solution  into 
•  a  large  stoppered  bottle.  Now  add  1  pint  of  strong  solution 
of  cyanide,  and  shake  well ;  4  ozs.  of  carbon  disulphide  are 
then  added,  as  also  2  or  3  ozs.  of  liquid  ammonia,  and  the 
bottle  again  well  shaken,  the  latter  operation  being  repeated 
every  two  or  three  hours.  The  solution  is  then  set  aside  for 
about  24  hours,  when  it  will  be  ready  for  use.  About  2  ozs. 
of  the  clear  liquid  may  be  added  to  every  20  gallons  of  plating 
solution,  and  well  mixed  by  stirring.  A  small  quantity  of  the 
brightening  solution  may  be  added  to  the  bath  every  day,  and 
the  liquid  then  gently  stirred.  In  course  of  time  the  disulphide 
^solution  acquires  a  black  color ;  to  modify  this  a  quantity  of 


DEPOSITION    OP    SILVER.  379 

strong  cyanide  solution,  equal  to  the  brightening  liquor  which 
has  been  removed  from  the  bottle,  should  be  added  each  time. 
In  adding  the  disulphide  solution  to  the  plating  bath,  an  ex- 
cess must  be  avoided,  otherwise  the  latter  will  be  spoiled. 
Small  doses  repeated  at  intervals  is  the  safer  procedure,  and 
less  risky  than  the  application  of  larger  quantities,  which  may 
-ruin  the  bath. 

A  very  simple  way  to  prepare  the  brightening  solution  is 
to  put  2  or  3  ozs.  of  carbon  disulphide  into  a  bottle  which 
holds  rather  more  than  half  a  gallon.  Add  to  this  about  3 
pints  of  old  silver  solution  and  shake  the  bottle  well  for  a 
minute  or  so.  Then  nearly  fill  the  bottle  with  a  strong  solu- 
tion of  cyanide,  shake  well  as  before,  and  set  aside  for  at  least 
24  hours.  Add  about  2  ozs.  (not  more)  of  the  brightening 
-liquor,  without  shaking  the  bottle,  to  each  20  gallons  of  solu- 
tion in  the  plating  vat.  Even  at  the  risk  of  a  little  loss  from 
-evaporation,  it  is  best  to  add  the  brightening  liquor  to  the 
bath  the  last  thing  in  the  evening,  when  the  solution  should 
be  well  stirred  so  as  to  thoroughly  diffuse  the  added  liquor. 
The  night's  repose  will  leave  the  bath  in  good  working  order 
for  the  following  morning. 

Yellow  tone  of  silvering.  After  plating,  the  objects  fre- 
quently show,  instead  of  a  pure  white,  a  yellow  tone,  or  they 
become  yellow  in  the  air,  which  is  ascribed  to  the  formation  of 
basic  silver  salts  in  the  deposit.  To  overcome  this  evil  it  has 
been  proposed  to  allow  the  objects  to  remain  in  the  bath  for  a 
few  minutes  after  interrupting  the  current,  whereby  the  basic 
salts  are  dissolved  by  the  potassium  cyanide  of  the  bath  ;  or 
the  same  object  is  attained  by  inverting  the  electrodes  for  a 
few  seconds,  after  plating,  thus  transforming  the  articles  into 
anodes.  The  electric  current  carries  away  the  basic  salt  of 
silver  in  preference  to  the  metal.  This  operation  should,  of 
course,  not  be  prolonged,  otherwise  the  silver  will  be  entirely 
removed  from  the  objects,  and  will  be  deposited  on  the  anodes. 
For  the  same  purpose  some  electro-platers  hold  in  readiness  a 
warm  solution  of  potassium  cyanide,  in  which  they  immerse 
the  plated  articles  for  half  a  minute. 


380  ELECTKO-DEPOSITION    OF    METALS. 

Silver  alloys.  It  has  been  proposed  to  add  to  the  silver 
baths  a  solution  of  nickelous  cyanide  in  potassium  cyanide  in 
order  to  obtain  a  deposit  of  a  silver-nickel  alloy,  which  is 
claimed  to  be  distinguished  by  its  greater  hardness  and  the 
property  of  not  so  readily  turning  dark.  Numerous  experi- 
ments with  solutions  of  cyanide  of  silver  and  nickelous  cyanide 
in  potassium  cyanide  in  all  possible  proportions,  and  with 
various  electro-motive  forces,  and  subsequent  analysis  of  the 
deposits  obtained,  showed,  however,  only  inconsiderable  traces 
of  nickel  in  the  silver  deposit,  which  had  but  a  very  slight 
influence  upon  the  hardness  and  durability  of  the  silver. 

The  London  Metallurgical  Co.  endeavors  to  attain  greater 
hardness  and  power  of  resistance  of  the  silver  by  adding  zinc 
cyanide  or  cadmium  cyanide,  and  has  given  to  this  process 
the  name  of  areas  silver-plating.  According  to  the  patent,  an 
addition  of  20  to  30  per  cent,  of  zinc  or  cadmium  to  the  silver 
prevents  the  tarnishing  of  the  plating,  and  besides  the  deposit 
is  claimed  to  be  lustrous  and  hard.  For  areas  silver-plating 
the  appropriate  quantity  of  zinc  or  cadmium,  or  a  mixture  of 
both  metals,  is  converted  into  potassium-zinc  cyanide  or 
potassium-cadmium  cyanide,  and  this  solution  is  mixed  with 
a  corresponding  quantity  of  solution  of  potassium-silver  cya- 
nide, with  a  small  excess  of  potassium  cyanide.  Sheets  of  a, 
silver-zinc  or  a  silver-cadmium  alloy  are  used  as  anodes. 

This  method  has  been  favorably  commented  upon  by 
Sprague,  Urquart  and  others,  and  some  English  platers  claim 
that  for  many  articles,  especially  bicycle  parts,  areas  silvering 
may  be  substituted  for  nickeling.  However  these  favorable 
opinions  were  not  confirmed  by  the  following  experiments 
made  by  Dr.  Langbein  regarding  the  value  of  this  process  as  a 
substitute  for  silver-plating  instruments  and  articles  of  luxury. 

A  bath  was  prepared  which  contained  per  quart  231J  troy 
grains  of  fine  silver  and  77  troy  grains  cadmium  in  the  form 
of  cyanide  double  salts  with  a  small  excess  of  potassium  cya- 
nide. The  most  suitable  tension  of  current  for  the  decompo- 
sition of  a  pure  potassium-cadmium  cyanide  solution  which 


DEPOSITION    OF    SILVER.  381 

-contained  per  quart  154  troy  grains  of  cadmium  with  the  same 
excess  of  potassium  cyanide  as  the  above-mentioned  mixture 
was  found  to  be  2  volts. 

In  electrolyzing  the  cadmium-silver  bath  with  0.75  volt,  a 
uniform  silver-white  deposit  similar  to  that  of  pure  silver  was 
-at  first  formed.  However,  after  two  hours  the  deeper  places 
of  the  objects  suspended  in  the  bath  showed  crystalline  excres- 
cences which  felt  sandy,  and  could  be  rubbed  off  with  the 
.fingers.  After  scratch-brushing  the  articles  and  again  sus- 
pending them  in  the  bath,  these  sandy,  non-adhering  metallic 
deposits  were  rapidly  reformed.  An  analysis  of  the  deposit 
separated  from  the  articles  showed  96.4  per  cent,  silver  and 
3.2  per  cent,  cadmium.  This  deposit  could,  without  difficulty, 
be  polished  with  the  steel  like  a  pure  silver  deposit,  and  hence 
its  hardness  would  not  seem  greater  than  that  of  pure  silver. 
Its  capability  of  resisting  hydrogen  sulphide  as  compared  with 
pure  silver  was  scarcely  greater. 

In  another  experiment  electrolysis  was  effected  with  1.25 
volts.  The  deposit  showed  from  the  start  a  coarser  structure, 
and  the  formation  of  the  sandy  non-adhering  deposit  took 
place  much  more  rapidly.  But,  on  the  other  hand,  the  hard- 
ness of  the  reduced  coherent  metal  was  greater  than  that  of 
pure  silver,  and  also  its  power  of  resisting  hydrogen  sulphide. 
An  analysis  of  the  deposit  showed  92.1  per  cent,  silver  and 
7.8  per  cent,  cadmium.  In  both  cases  the  deposit  was  dull 
like  that  of  pure  silver. 

With  a  greater  electro-motive  force  the  quantity  of  cad- 
mium in  the  deposit  increased,  and  the  hardness  of  the  latter 
became  correspondingly  greater.  However,  these  deposits 
could  not  be  considered  serviceable  for  the  above-mentioned 
purpose,  because  they  could  not  be  made  of  sufficient  thick- 
ness as  required  for  solid  silver-plating  of  forks  and  spoons. 

In  Dr.  Langbein's  opinion,  the  decomposition-pressures  of  a 
solution  of  potassium-silver  cyanide  and  of  one  of  potassium- 
•cadmium  cyanide  lie  too  far  apart  to  obtain  without  delay 
deposits  of  even  composition  and  of  sufficient  density  and 
thickness. 


382  ELECTRO-DEPOSITION    OF    METALS. 

Execution  of  silver-plating — A.  Silver-plating  by  weight. — 
Copper,  brass,  and  all  other  copper  alloys  may  be  directly 
plated  after  amalgamating  (quicking),  whilst  iron,  steel,  nickel, 
zinc,  tin,  lead,  and  Britannia  are  first  coppered  or  brassed,  and< 
then  amalgamated. 

The  mechanical  and  chemical  preparation  of  the  objects  for 
the  silver-plating  process  is  the  same  as  described  on  page  188 
et  seq.  To  obtain  well-adhering  deposits  great  care  must  be 
exercised  in  freeing  the  objects  from  grease,  and  in  pickling. 
As  a  rule,  objects  to  be  silver-plated  are  ground  and  polished. 
However,  polishing  must  not  be  carried  too  far,  since  the  de- 
posit of  silver  does  not  adhere  well  to  highly  polished  surfaces; 
and  in  case  such  highly  polished  objects  are  to  be  silvered  it 
is  best  to  deprive  them  of  their  smoothness  by  rubbing  with 
pumice  powder,  emery,  etc.,  or  by  pickling. 

The  treatment  of  copper  and  its  alloys,  German  silver  and 
brass,  which  have  chiefly  to  be  considered  in  plating  by 
weight  is,  therefore,  as  follows  : 

1.  Freeing  from  grease  by  hot  potash  or  soda  lye  (1  part  of 
caustic  alkali  to  8  to  10  parts  of  water),  or  by  brushing  with 
the  lime-paste  mentioned  on  page  229. 

2.  Pickling  in  a  mixture  of  1  part,  by  weight,  of  sulphuric 
acid  of  66°   Be.    and  10  of  water.     This   pickling   is  only 
required  for  rough  surfaces  of  castings,  ground  articles  being 
immediately  after  freeing  from  grease  treated  according  to  3. 

3.  Rubbing  with  a  piece  of  cloth  dipped  in  fine  pumice- 
powder  or  emery,  after  which  the  powder  is  to  be  removed  by 
washing. 

4.  Pickling  in  the  preliminary  pickle,  rinsing  in  hot  wateiv 
and  quickly  drawing  through  the  bright-dipping  bath  (page 
223),  and  again  thoroughly  rinsing  in  several  waters. 

5.  Amalgamating  (quicking)  by  immersion  in  a  solution  of 
mercury,  called  the  quicking  solution.     This  consists  of  a  solu- 
tion of  0.35  ounce  of  nitrate  of  mercury  in  1  quart  of  water,, 
to  which,  while  constantly  stirring,  pure  nitric  acid  in  small 
portions  is  added  until  a  clear  fluid  results.     A  weak  solution 


DEPOSITION    OF    SILVER.  383 

of  potassium-mercury  cyanide  in  water  is,  however,  to  be  pre- 
ferred, because  the  acid  quicking  solution  mentioned  above 
makes  the  metals  brittle.  A  quicking  solution  for  silver- 
plating  by  weight  consists  of:  Potassium-mercury  cyanide,  14 
drachms  to  1  oz.  ;  99-per  cent,  potassium  cyanide,  14  drachms; 
water,  1  quart.  Care  must  be  taken  to  bring  the  quicked 
objects  into  the  bath  as  rapidly  as  possible,  otherwise  thin 
objects  are  liable  to  become  brittle.  The  amalgam  formed 
upon  the  surface  penetrates  to  the  interior  of  thin  sheets  if 
this  action  is  not  prevented  by  an  immediate  deposition  of 
silver  and  the  formation  of  silver  amalgam.  In  the  quicking 
solution  the  objects  remain  only  long  enough  to  acquire  a 
uniform  white  coating,  when — 

6.  They  are  rinsed  in  clean  water,  and  gone  over  with  a 
soft  brush  in  case  the  quicking  shows  a  gray  instead  of  a 
white  tone. 

The  articles  are  now  brought  into  the  silver  bath,  and 
secured  to  the  object-rods  by  slinging  wires  of  pure 
copper  or,  still  better,  of  pure  silver.  The  latter 
have  the  advantage  that  when  by  reason  of  a  de- 
posit of  considerable  thickness  having  been  formed 
upon  them  they  have  become  useless  for  suspend- 
ing the  articles,  they  can  be  directly  converted  into 
silver  nitrate  by  dissolving  in  nitric  acid,  and  used 
for  the  preparation  of  fresh  baths,  or  for  strengthen- 
ing old  baths. 

When  certain  objects,  for  instance,  forks  and 
spoons,  are  to  be  plated,  copper  wires  may  be  bent  in  the  man- 
ner shown  in  Fig.  124.  To  prevent  the  deposition  of  silver 
upon  the  portions  of  the  wire  which  do  not  serve  for  the  pur- 
pose of  contact,  they  are  coated  with  fused  ebonite  mass  or 
gutta-percha,  only  the  loop  in  which  the  fork  or  spoon  is  hung 
and  the  upper  end  for  suspending  to  the  object-rod  being  left 
free.  Silver  wires  are  also  better  for  this  purpose. 

In  order  to  secure  an  extra  heavy  coating  of  silver  on  the 
convex  surfaces  of  spoons  and  forks  which,  being  subject  to 


384  ELECTRO-DEPOSITION    OF    METALS. 

greater  wear  than  the. other  parts,  require  extra  protection, 
some  plating  establishments  use  a  frame  in  which  the  articles 
supported  therein  by  their  tips  are  placed  horizontally  in  a 
shallow  silver  bath  and  immersed  just  deep  enough  to  allow 
the  projecting  convexities  to  dip  into  the  bath.  By  this  arti- 
fice these  portions  are  given  a  second  coating  of  silver  of  any 
desired  thickness.  This  mode  of  procedure,  which  is  termed 
;<  sectional  "  plating,  accomplishes  the  intended  purpose  nicely 
and  satisfactorily.  In  some  establishments  the  silvered  forks 
and  spoons  are  placed  between  plates  of  gutta-percha  of  corre- 
sponding shape,  and  held  together  by  rubber  bands.  In  these 
plates  the  portions  to  be  provided  with  an  extra  coating  of 
silver  are  cut  out.  By  suspending  the  forks  and  spoons  thus 
protected  in  the  bath,  the  unprotected  places  receive  a  further 
layer  of  silver,  the  outlines  of  which  are  later  on  smoothed 
down  with  burnishers.  The  second  object  may  also  be  at- 
tained by  coating  the  places  which  are  to  receive  no  further 
deposit  with  "  stopping-off "  varnish  (see  later  on). 

According  to  German  patent  No.  76975,  sheets  of  celluloid 
or  similar  substances  are  suspended  as  shields  between  the 
inside  portions  of  spoons  and  the  anodes.  By  this  means  the 
deposit  of  silver  on  these  portions,  which  are  subject  to  less 
wear,  is  only  slightly  augmented,  while  the  outside  portions 
acquire  a  heavier  deposit. 

To  attain  the  same  object,  J.  Buck  *  suspends  a  frame  in 
such  a  manner  that  every  two  spoons  are  turned  with  their 
inside  portions  towards  each  other,  and  anodes  are  arranged 
only  on  the  outside  portions. 

When  commencing  the  operation  of  silver-plating,  intro- 
duce into  the  bath  at  first  a  somewhat  more  powerful  current, 
so  that  the  first  deposition  of  silver  takes  place  quite  rapidly } 
and  after  3  minutes  regulate  the  current  so  that  in  10  to  15 
minutes  the  objects  are  coated  with  a  thin,  dull  film  of  silver. 
At  this  stage  take  them  from  the  bath,  and  after  seeing  that 

*  German  patent  126053  (expired). 


DEPOSITION    OF    SILVER.  385 

all  portions  are  uniformly  coated,  scratch-brush  them  with  a 
brass  brush,  which  should,  however,  not  be  too  fine.  In 
doing  this  the  deposit  must  not  raise  up.  If  at  this  stage  the 
objects  stand  thorough  scratch-brushing,  raising  of  the  deposit 
in  burnishing  later  on  need  not  be  feared. 

Any  places  which  show  no  deposit  are  vigorously  scratch- 
brushed  with  the  use  of  pulverized  tartar,  then  again  carefully 
cleansed  by  brushing  with  lime-paste  to  remove  any  impuri- 
ties due  to  touching  with  the  hands,  pickled  by  dipping  in 
potassium  cyanide  solution,  again  rinsed,  quicked,  and  after 
careful  rinsing  returned  to  the  bath.  Special  care  must  be 
taken  not  to  contaminate  the  bath  with  quick  ing  solution  as 
this  would  soon  spoil  it. 

The  objects  now  remain  in  the  bath  at  a  normal  current- 
density  until  the  deposit  has  acquired  a  weight  corresponding 
to  the  desired  thickness.  Knives,  forks  and  spoons  receive  a 
deposit  of  2.11  to  3.52  ozs.  of  silver  per  dozen. 

Considerable  difficulty  is  sometimes  experienced  in  silver 
plating  the  steel  blades  of  table  knives  as  the  silver  will  strip 
or  pull  off  of  the  blade  after  it  has  been  in  use  a  short  time. 
According  to  Mr.  Charles  H.  Proctor*  this  difficulty  is  due  to 
unsatisfactory  conditions  at  the  time  of  deposition.  The  coat- 
ing of  the  knives  with  copper  previous  to  silver  plating  will 
not  improve  matters;  in  fact  this  method  has  been  discarded 
as  a  failure  by  all  the  manufacturers  of  silver-plated  steel- 
knives  and  forks  years  ago.  The  most  satisfactory  method  to 
pursue  is  to  reduce  all  the  silver  from  the  surface  of  the  knives 
by  the  aid  of  a  strong  cyanide  solution  and  a  strong  reversed 
current  of  five  to  six  volts  or  more.  For  cathodes  use  carbon 
and  arrange  the  positive  pole,  upon  which  the  knives  are 
placed,  so  that  the  carbon  cathodes  will  be  placed  on  either 
side  of  the  knives,  as  in  a  regular  bath,  so  that  the  metal  is 
reduced  uniformly.  After  the  silver  is  removed  the  surface  is 
washed,  dried  and  polished  and  then  the  knives  should  be 

*The  Metal  Industry,  December,  1912. 
25 


386  ELECTRO-DEPOSITION    OF    METALS. 

boiled  out  in  any  of  the  usual  alkaline  solutions  of  potash  or 
soda.  Then  immerse  them  in  undiluted  hydrochloric  acid 
and  wash  and  scour  on  a  tampico  wheel,  using  sodium  carbon- 
ate in  the  water  to  prevent  rusting  after  scouring. 

The  articles  are  now  ready  for  the  bath.  Frame  up,  wash 
in  clean  water,  immerse  in  a  50  per  cent,  solution  of  hydro- 
chloric acid  and  water,  rewash  and  immerse  directly  in  the 
strike  solution.  This  strike  should  consist  of:  Potassium 
cyanide  8  ozs.,  silver  chloride  \  oz.,  water  1  gallon. 

The  voltage  should  be  from  one  to  one  and  one-half  volts 
with  the  full  amperage  of  the  dynamo,  and  the  immersion 
from  fifteen  to  thirty  seconds.  The  knives  should  then  be 
placed  in  the  regular  silver  bath.  This  bath  should  have 
very  little  free  cyanide  and  should  be  run  at  a  voltage  not 
exceeding  one  and  one-half.  The  amperage  should  be  about 
three  per  dozen  of  knives,  or  four  amperes  per  square  foot  of 
exposed  surface.  This  is  the  method  used  by  the  majority  of 
the  large  concerns. 

Some  platers  use  a  first  and  second  strike.  In  this  case  the 
first  solution  consists  of  a  solution  of  cyanide  in  the  propor- 
tion of  six  to  eight  ounces  per  gallon  and  one-eighth  to  one- 
quarter  ounce  of  silver  in  the  form  of  chloride.  Two  copper 
anodes  are  used,  about  three  by  eight  inches,  and  two  small 
silver  anodes,  about  one-fourth  the  dimensions  of  the  copper 
anodes.  No  deposit  shows  on  the  steel  after  the  immersion  in 
this  strike.  The  knives  are  then  immersed  directly  in  the 
second  strike,  as  before  mentioned,  and  then  into  the  bath. 
No  copper  should  show  from  the  copper  and  silver  strike,  and 
as  soon  as  any  becomes  observable  on  the  knives,  more  cya- 
nide should  be  added  to  the  bath.  This  is  practically  only 
an  electric  cleaner.  For  the  deposit  of  silver,  by  following 
the  above  instructions  carefully,  no  trouble  with  peeling  of 
the  deposit  will  be  experienced. 

Determination  of  weight.  In  order  to  control  the  weight  of 
the  deposit,  proceed  as  follows  :  Remove  one  of  the  pans  of  a 
sensitive  beam  balance  and  substitute  for  it  a  brass  rod  which 


.DEPOSITION    OF    SILVER. 


387 


keeps  the  other  pan  in  equilibrium.  Under  this  rod  place  a 
vessel  filled  with  pure  water,  and  of  sufficient  diameter  and 
depth  to  allow  of  the  article  suspended  to  the  rod  dipping 
entirely  into  the  water  without  touching  the  sides  of  the  vessel. 
Suppose  now  that  several  dozen  spoons  of  the  same  size  and 
shape  are  at  the  same  time  to  be  provided  with  a  deposit  of 

FIG.  125. 


a  determined  weight,  it  suffices  to  control  the  weight  of  the 
deposit  of  a  single  spoon,  and  when  this  has  acquired  the 
necessary  deposit  all  the  other  spoons  will  also  be  coated  with 
a  deposit  of  silver  of  the  same  thickness  as  the  test  spoon.  The 
spoons  having  been  quicked  and  carefully  rinsed,  one  of  them 
is  suspended  to  the  brass  rod  of  the  balance  so  that  it  dips  en- 


338 


ELECTRO-DEPOSITION    OF    METALS. 


FIG.  126. 


tirely  under  water.  The  equilibrium  is  then  re-established  by 
placing  lead  shot  upon  the  pan  of  the  scale,  and  adding  the 
weight  corresponding  to  the  deposit  the  spoon  is  to  receive. 
Now  bring  the  weighed  spoon  together  with  the  rest  into  the 
bath,  and  proceed  with  the  silvering  process  in  the  ordinary 
manner.  After  some  time  the  weighed  spoon  is  taken  from 
the  bath,  rinsed  in  water,  and  hung  to  the  brass  rod  of  the 
scale.  If  it  does  not  restore  the  equilibrium  of  the  latter,  it  is 
returned  to  the  bath,  and  after  some  time  again  weighed,  and 
so  on  until  its  weight  corresponds  to  that  of  the  lead  shot  and 
weight  placed  in  the  pan  of  the  scale,  when  it  is  assumed  that 
the  other  objects  have  also  received  their  proper  quantity  and 
that  the  operation  is  complete. 

A  more  complete  weighing  apparatus  is  the  metallometric 
balance  first  used  by  Brandely,  and  later  on  improved  by 
Roseleur.  The  apparatus,  which  is  shown  in  Fig.  125,  is 
designed  for  obtaining  deposits  of  silver  "  with- 
out supervision  and  with  constant  accuracy, 
and  which  spontaneously  breaks  the  current 
when  the  operation  is  terminated."  It  is 
manufactured  in  various  sizes,  suitable  for 
small  or  large  operations. 

It  consists  of:  1.  A  wooden  vat,  the  upper 
edge  of  which  carries  a  brass  winding-rod  hav- 
ing a  binding  screw  at  one  end  to  receive  the 
positive  conducting  wire  of  the  battery.  From 
this  rod  the  anodes  are  suspended,  which  are 
entirely  immersed  in  the  solution,  and  com- 
municate with  brass  cross-rods  by  means  of 
platinum  wire  hooks.  These  cross-rods  are 
flattened  at  their  ends  so  that  they  may  not 
roll,  and  at  the  same  time  have  a  better  contact  with  the 
11  winding-rod."  2.  A  cast-iron  column  screwed  at  its  base 
to  the  side  of  the  vat,  and  which  carries  near  the  top  two  pro- 
jecting arms  of  cast-iron,  the  extremities  of  which  are  vertical 
and  forked,  and  may  be  opened  or  closed  by  iron  clamps. 


DEPOSITION    OF    SILVER.  389 

These  forks  are  intended  for  sustaining  the  beam  and  prevent- 
ing the  knives  from  leaving  their  bearings  under  the  influ- 
ence of  too  violent  oscillations.  In  the  middle  of  the  two 
arms  are  two  wedge-shaped  recesses  of  polished  steel  to  receive 
the  knife  edges  of  the  beam.  One  of  the  arms  of  the  column 
carries  at  its  end  a  horizontal  ring  of  iron  in  which  is  fixed 
a  heavy  glass  tube  supporting  a  cup  of  polished  iron  which  is 
insulated  from  the  column  (Fig.  126). 

This  cup  has  at  its  lower  part  a  small  pocket  of  lamb-skin 
or  of  India  rubber,  which  by  means  of  a  screw  beneath  may 
be  raised  or  lowered.  This  flexible  bottom  allows  the  opera- 
tor to  lower  or  raise  at  will  the  level  of  the  mercury  intro- 
duced afterwards  into  the  iron  cup.  Another  lateral  screw 
permits  connection  to  be  made  with  the  negative  electrode. 
3.  A  cast-iron  beam  carrying  in  the  middle  two  sharp  knife 
edges  of  the  best  steel  hardened  and  polished.  At  each  ex- 
tremity there  are  two  parallel  bearings  of  steel  separated  by  a 
notch,  and  intended  for  the  knife-edges  of  the  scale-pan  that 
receives  the  weights,  and  those  of  the  frame  supporting  the 
articles  to  be  plated.  One  of  the  arms  of  the  beam  is  pro- 
vided with  a  stout  platinum  wire,  placed  immediately  above 
and  in  the  center  of  the  cup  of  mercury.  According  as  the 
beam  inclines  one  way  or  the  other,  this  wire  plays  in  or  out 
of  the  cup.  4.  A  scale-pan  for  weights,  with  two  knife-edges 
of  cast  steel,  which  is  attached  to  four  chains  supporting  a 
wooden  pan  for  the  reception  of  weights.  A  smaller  pan 
above  is  intended  for  the  weights  corresponding  to  that  of  the 
silver  to  be  deposited.  5.  The  frame  for  supporting  the 
articles  to  be  plated,  which  is  also  suspended  from  two  steel 
knife-edges,  and  the  rod  of  which  is  formed  of  a  stout  brass 
tube  attached  below  to  the  brass  frame  proper,  which  last  is 
equal  in  dimensions  to  the  opening  of  the  vat,  and  supports 
the  rods  to  which  the  articles  are  suspended. 

It  must,  however,  be  borne  in  mind  that  the  weight  of  a 
body  immersed  in  water  is  less  than  when  weighed  in  the  air, 
it  being  as  much  less  as  the  weight  of  the  volume  of  fluid  dis- 


390  ELECTRO-DEPOSITION    OF    METALS. 

placed  by  it.  The  specific  gravity  of  silver  is  10.5,  hence  1 
cubic  centimeter  of  silver  weighs  10.5  more  than  1  cubic 
centimeter  of  water,  so  that  10.5  grammes  of  silver  weighed 
in  the  air  weigh  only  10.5  —  1  =  9.5  grammes  when  im- 
mersed in  water.  Since  the  specific  gravity  of  the  silver  bath 
Is  greater  than  that  of  water — of  fresh  baths  about  5°  Be  = 
1.035  — 10.5  grammes  of  silver,  while  immersed  in  the  silver 
.bath,  weigh  only  10.5  —  1.035  =  9.465  grammes.  Hence  for 
the  determination  of  the  weight  to  be  placed  in  the  scale-pan, 
which  corresponds  to  the  actual  weight  of  the  silver  deposit, 
the  desired  weight  of  the  deposit  has  to  be  multiplied  by  9.465 
and  divided  by  10.5,  or  what  amounts  to  the  same  thing, 
multiplied  by  0.901.  Suppose  300  grammes  of  silver  are  to 
be  deposited  upon  forks,  knives  and  spoons,  not  300  grammes, 
but  only  300  X  0.901  =  270.3  grammes  have  to  be  placed  in 
the  scale-pan.  The  weight  of  the  articles  themselves  is  not 
taken  into  account  as  the  objects  are  tared  under  the  solution 
and  remain  in  the  same  bath-fluid  to  the  end  of  the  process. 
Hence,  according  to  the  above  calculation,  the  weight,  to  be 
placed  in  the  scale-pan  should,  in  round  figures,  be  10  per 
cent,  less  than  the  desired  weight  of  silver.  However,  as 
silver  also  deposits  on  the  slinging  wires,  it  has  been  shown 
that  a  reduction  of  4  to  5  per  cent,  of  the  weight  is  about  the 
right  thing. 

Fig.  127  shows  a  metallometric  balance  in  operation,  as 
coupled  with  the  rheostat,  voltmeter,  and  the  silver  bath,  and 
will  be  understood  without  further  explanation.  These  metal- 
lometric balances  must  of  course  be  very  carefully  constructed 
so  as  to  render  possible  accurate  weighings  with  a  load  of 
about  11  Ibs.  They  are  used  by  most  large  silver-plating 
establishments  for  forks,  knives  and  spoons.  They  may  also 
be  employed  to  advantage  in  plating  coffee-pots,  tea-pots, 
sugar  bowls,  etc.,  but  with  such  articles  special  attention  has 
to  be  paid  to  the  anode  arrangement  in  order  to  obtain  a 
deposit  of  uniform  thickness  upon  all  portions.  It  is  evident 
that  with  the  use  of  straight  silver  anodes  the  portions  of 


DEPOSITION    OP    SILVER. 


391 


round  vessels  nearest  to  the  anodes  will  receive  a  thicker  de- 
posit of  silver  than  the  portions  at  a  greater  distance  from 
them.  However,  this  also  happens  in  every  silver  bath  in 
operation  not  connected  with  a  metallometric  balance,  the 
latter  indicating  of  course  only  the  total  weight  of  deposit 
upon  all  the  articles  in  the  bath,  and  means  for  the  formation 

FIG.  127. 


of  a  uniform  deposit  on  all  portions  must  therefore  be  pro- 
vided. This  is  effected  by  the  use  of  curved  anodes  suspended 
around  the  objects  at  equal  distances;  further  by  frequently 
•changing  the  position  of  the  objects  so  as  to  bring  the  more 
remote  portions  nearer  to  the  anodes. 

For  the  determination  of  the  weight  of  the  deposit,  Pfan- 


392  ELECTRO-DEPOSITION    OF    METALS. 

hauser  Jr.  uses  a  voltametric  balance,*  a  combination  of  a 
voltameter  with  a  balance,  the  principle  of  which,  according 
to  Ferchland,f  is  similar  to  Edison's  registering  voltameter, 
and  has  for  some  time  been  practically  utilized  by  Prof. 
Domalip  J  in  Prague. 

A  copper  voltameter  is  an  apparatus  which  allows  of  the 
determination  of  the  quantity  of  current  conducted  in  a  cer- 
tain time  through  an  acid  copper  sulphate  solution  (water  35 
ozs.,  copper  sulphate  7  ozs.,  concentrated  sulphuric  acid  If 
ozs.,  alcohol  J  oz.)  by  the  quantity  of  copper  electrolytically 
separated  on  the  cathode.  Two  copper  anodes  dip  into  the 
solution  and  between  them  is  a  copper  cathode.  The  weight 
of  the  latter  is  exactly  determined,  and  after  the  current  has 
for  an  accurately  measured  time  passed  through  the  volta- 
meter, is  washed  with  water,  rinsed  with  alcohol,  dried  and 
again  weighed.  From  the  increase  in  weight  the  quantity  of 
current  which  has  passed  through  the  voltameter  can  be 
readily  calculated,  since  one  ampere  deposits  in  one  hour 
1.1858  grammes  of  copper. 

Now  by  placing  such  a  copper  voltameter  in  the  current- 
conductor  of  a  silver  bath  so  that  the  current  passes  through 
the  bath  and  the  voltameter  one  after  the  other,  the  same 
quantity  of  current  must  pass  through  the  bath  as  well  as  the 
voltameter  since,  according  to  KirchhofFs  law,  the  current- 
strength  is  equally,  great  in  all  points  of  a  current-circuit. 
According  to  Faraday's  law,  the  quantities  of  metals  de- 
posited are  proportional  to  their  electro-chemical  equivalents 
and  hence  the  quantity  of  copper  separated  will  be  to  the 
quantity  of  silver  deposited  as  1.858  :  4.0248  ;  thus  when  the 
quantity  of  copper  separated  is  known,  the  weight  of  the  silver 
deposit  can  be  readily  calculated. 

In  Pfanhauser's  voltameter  balance  the  copper  cathode  is 

*  German  patent  120843. 

f  Zeitschrift  fur  Elektrochemie,  1891,  No.  71. 

J  Ahrens,  Handbuch  der  Elektrochemie,  ii,  Aufl.  S.  151, 


DEPOSITION    OF    SILVER.  393 

by  means  of  a  conductor  suspended  to  the  metal-beam  of  a 
smaller  balance,  the  equilibrium  being  restored  by  placing 
weights  or  shot  in  the  scale-pan  on  the  other  end  of  the  beam. 
Now  in  order  to  determine  the  weight  adequate  to  the  desired 
deposit  in  the  silver  bath,  the  weight  has  to  be  multiplied  by 
1.1858  and  divided  by  4.0248,  The  number  of  grammes 
found  is  the  weight  the  copper-deposit  in  the  copper  volta- 
meter must  attain  to  correspond  to  the  desired  weight  of  the 
deposit  in  the  silver  bath.  The  weight  thus  determined  has 
to  be  placed  in  the  pan  of  the  scale.  When  the  deposit  has 
acquired  the  desired  weight  the  current  is  automatically  in- 
terrupted by  a  contrivance  similar  to  that  described  when 
speaking  of  the  metallometric  balance. 

As  compared  with  the  metallometric  balance,  the  voltametric 
balance  possesses  advantages  and  disadvantages,  the  latter 
being  chiefly  that  besides  the  swelling-up  of  the  deposit  in  the 
voltameter,  which  has  to  be  taken  into  consideration,  the  re- 
duction of  the  weight  of  silver  to  be  deposited  to  the  weight  of 
the  copper  deposit  to  be  placed  in  the  scale-pan  may  readily 
lead  to  errors  if  left  to  the  ordinary  workman.  To  be  sure, 
this  can  be  avoided  by  consulting  tables  which  are  furnished 
with  the  balance. 

It  must  furthermore  be  borne  in  mind  that  the  voltametric 
balance  gives  reliable  results  only  when  the  current-output  of 
the  silver  bath  remains  constant  and  is  exactly  equal  to  that  of 
the  copper  solution  in  the  voltameter,  a  third  correction  of  the 
weight  being  otherwise  required.  The  current-output  in  the 
voltameter  is  100,  but  that  of  fresh  silver  baths  does  not  reach 
this  height.  According  to  numerous  determinations  by  Friess- 
ner,  executed  in  Dr.  G.  Langbein  &  Co.'s  electro-chemical 
laboratory,  the  current-output  in  cyanide  silver  baths  varies 
according  to  whether  the  bath  is  at  rest- or  in  motion,  the  cur- 
rent-output with.  0.3  ampere  current-density  being  in  a  bath 
which  contains  per  liter  25  grammes  of  silver  as  silver  cya- 
nide and  27  grammes  99-percent  potassium  cyanide,  99.63  per 
cent,  without  agitation  of  the  bath,  and  99.18  per  cent,  with 
agitation,  hence  0.45  per  cent,  less  in  the  latter  case. 


394  ELECTRO-DEPOSITION    OF    METALS. 

The  increased  electro-motive  force  when  a  voltametric  bal- 
ance is  placed  in  the  current-circuit  must  also  not  be  lost 
sight  of.  Since  the  voltameter  solution  and  the  silver  bath 
are  coupled  one  after  the  other,  about  double  the  electro- 
motive force  is  required,  and  this  greater  performance  of  work 
increases  the  cost  of  current.  However,  this  is  not  of  sufficient 
importance  to  prevent  the  use  of  voltametric  balances. 

The  advantages  of  a  voltametric  balance  consist  in  that  it 
is  not  necessary  to  place  it  in  the  vicinity  of  the  bath.  It  may 
be  located  in  a  special  dry  room  where  it  is  not  exposed  to  the 
effects  of  the  damp  atmosphere  of  the  work-room.  However, 
these  effects  are  as  a  rule  over-estimated,  since  metallometric 
balances  with  knife-edges  of  specially  prepared  steel,  which 
quite  well  resists  the  action  of  rust,  working  in  agate  bearings, 
have  been  known  to  work  with  great  accuracy  after  having 
been  in  use  for  fifteen  years.  The  slighter  load  of  the  beams 
is  also  in  favor  of  metallometric  balances,  so  that  they  can  be 
of  lighter  construction. 

Metallometric  as  well  as  voltametric  balances  have  the 
drawback  that  the  current  must  pass  through  the  beam  and 
other  sensitive  parts  to  reach  the  bath.  To  prevent  corrosion 
on  the  contacts  and  avoid  large  sparks  on  the  sensitive  por- 
tions, special  protective  measures  are  required  which  render 
the  construction  both  more  complicated  and  more  expensive. 

The  advantage  of  metallometric  balances,  namely,  simple 
-attendance  and,  when  due  care  is  observed,  absolute  certainty 
of  results,  may  be  advantageously  utilized,  together  with  the 
advantages  of  voltametric  balances,  i.  e.,  slighter  load  and 
location  at  any  desired  distance  from  the  bath,  by  the  follow- 
ing combination  devised  by  Neubeck. 

If  in  front  of  the  silver  bath  be  placed  a  smaller  controlling 
bath  of  exactly  the  same  composition  as  the  silver  bath  in 
operation,  or  in  other  words,  is  taken  from  the  latter,  the  cur- 
rent-output of  both  these  baths  must  be  the  same,  provided 
the  current-density  is  the  same.  Now  by  using  as  cathodes 
ifor  this  controlling  bath  very  thin  silver  sheets — 0.05  to  0.1 


DEPOSITION    OF    SILVER. 


395 


millimeter  thick — with  a  total  surface  approximately  equal  to 
that  of  the  objects  in  the  bath,  the  weight  of  the  cathodes  will, 
on  the  other  hand,  be  materially  less  than  that  of  the  articles 
in  the  bath,  for  instance,  of  an  equally  large  surface  repre- 
sented by  spoons,  and  consequently  the  balance  can  be  of 
lighter  construction,  while,  on  the  other  hand,  the  current- 
density  in  the  controlling  bath  will  be  approximately  equal 
to  that  in  the  silver  bath. 

One  dozen  spoons  weigh  on  an  average  540  to  550  grammes 
-and  have  a  surface  of  about  13.2  square  decimeters.     The  same 

FIG.  128. 


surface  in  silver  sheet,  0.1  millimeter  thick,  weighs  about  70 
grammes,  and  in  silver  sheet,  0.05  millimeter  thick,  about  35 
•grammes.  Hence  the  load  of  the  ware  is,  in  the  commence- 
ment, 1\  to  15  times  less  than  with  the  metallometric  balance 
and  when,  on  attaining  a  thickness  of  about  \  millimeter,  the 
cathodes  are  reversed,  always  only  half  as  great. 

Now  by  allowing  the  current  to  pass  through  the  control- 
ling bath  and  then  through  the  silver  bath,  exactly  the  same 
quantity  of  silver  is  deposited  in  the  former  as  in  the  latter ; 


396  ELECTRO-DEPOSITION    OF    METALS. 

thus  by  connecting  the  cathodes  of  the  controlling  bath  with 
a  balance,  the  quantity  of  metal  deposited  in  the  silver  bath 
upon  the  objects  can  be  accurately  determined. 

These  considerations  led  to  the  construction  of  the  volta- 
metric  controlling  apparatus,  Fig.  128,  which  can  be  connected 
with  any  kind  of  cheap  beam-balance.  The  apparatus  *  con- 
structed by  Dr.  G.  Langbein  &  Co.  is  arranged  as  follows  : 

The  screw  1  secured  to  the  anode-frame  (Fig.  128)  is  directly 
connected  with  the  anode  wire.  Upon  the  anode-frame  of 
copper  sit  the  conducting  rods  9,  9,  9,  etc.,  for  the  anodes,  the 
latter  being  secured  to  them  by  means  of  platinum  wire.  To 
the  rod  16  is  secured  the  movable  cathode  from  7,  to  which 
the  thin  cathode  sheets  are  suspended  by  means  of  platinum 
wire.  The  current  enters  the  bath  through  the  binding-post 
1,  the  anode-rods  9,  and  the  anodes,  passes  to  the  cathodes, 
and  returns  through  the  cathode-frame  7  to  the  source  of  cur- 
rent so  long  as  the  screw  2  fixed  to  the  support  17  dips,  by 
reason  of  the  load  of  the  balance,  into  the  mercury  vessel  3, 
The  latter  is  secured  to  the  anode-frame  7  and  conductively 
connected  with  it.  The  celluloid  disk  10  serves  the  purpose 
of  protecting  the  bath  from  mercury,  which  may  be  spilled  by 
careless  handling,  passing  into  it. 

When  the  cathodes  have  attained  the  required  weight  the 
flow  of  current  to  the  bath  is  interrupted  by  the  beam  of  the 
balance  tilting  over.  The  two  steel  pins  4  and  5,  which  are 
insulated  from  the  mercury  vessel  3,  dip  thereby  into  the  mer- 
cury cups  6  fixed  below  them  on  the  movable  arm  of  the 
support  17  and  insulated  one  from  the  other,  the  short-circuit 
of  the  bell  wire  being  thus  effected.  The  wire  11  leads  direct 
to  the  bell  13,  while  a  second  wire  12  leads  through  the  spirals 
14  to  the  support  17  and  from  there  through  spiral  15  to  the 
bell.  When  the  pins  4  and  5  dip  into  the  mercury  cups,  6,  a 
second  connection  with  the  bell  is  made  and  the  latter  rings 
so  long  as  the  pins  4  and  5  dip  into  the  mercury. 

*  German  patent. 


DEPOSITION    OF    SILVER.  397 

Contrary  to  the  principle  of  the  metallometric  and  the  volta- 
metric  balances,  the  beam  and  other  portions  of  the  balance 
are  here  entirely  excluded  from  the  current-circuit.  Hence, 
any  ordinary  beam-balance  can  be  used  and  no  corrosion  of 
sensitive  portions  of  the  balance  by  sparks  takes  place. 

When  the  cathodes  of  the  controlling  bath  have  attained  a 
thickness  approximately  the  same  as  that  possessed  by  the 
silver  anodes  of  the  bath  in  the  commencement  of  the  opera- 
tion, they  are  used  as  anodes  by  suspending  them  to  the 
anode-rods,  while  the  anodes  which  have  become  thinner  are 
suspended  as  cathodes. 

With  this  arrangement  there  is  to  be  sure,  the  same  draw- 
back as  with  the  voltametric  balance,  namety,  that  by  reason 
of  the  baths  being  coupled  one  after  the  other,  double  the 
electro-motive  force  than  that  used  for  a  silver  bath  connected 
with  a  metallometric  balance  is  required.  The  interest,  which, 
however,  amounts  to  very  little,  on  the  dead  metallic  silver  in 
the  controlling  bath  may  also  be  called  a  disadvantage.  On 
the  other  hand,  the  controlling  apparatus  has  the  advantage 
that  two  or  more  silver  baths  of  the  same  composition  can  be 
connected  with  it  when  the  same  quantity  of  silver  is  to  be 
deposited  upon  approximately  the  same  object -surface  in  each 
bath. 

The  case  is  somewhat  different  when  the  baths  in  operation 
are  of  considerable  size  and  furnished  with  many  object-rods. 
In  order  to  obtain  the  same  current-density  in  the  actual  silver 
bath  as  in  the  controlling  bath,  the  latter  would  have  to  be  of 
quite  large  dimensions  and  require  so  much  electrode-material 
as  to  cause  considerable  expense  for  providing  it.  In  such  a 
•case  the  advantages  presented  by  the  same  composition  of  the 
operating  bath  and  the  controlling  bath  have  to  be  abandoned 
and  the  controlling  bath  has  to  be  used  as  a  copper  voltameter. 
Since  in  the  copper  solution  depositions  can  be  made  with  cur- 
rent-densities up  to  1.5  amperes  per  square  decimeter  only  one- 
fifth  part  of  the  object-surface  in  the  operating  bath  is  required 
as  cathode  surface  in  the  controlling  copper  bath.  Of  course 


398  ELECTRO-DEPOSITION    OF    METALS. 

the  weight  of  the  desired  silver  deposit,  reduced  to  copper,, 
which  is  found  from  tables  furnished  with  the  apparatus,  has- 
to  be  placed  in  the  scale-pan.  The  tables  are  calculated  for 
current-outputs  of  from  98  to  99.6  per  cent,  in  TV  per  cent,  for 
baths  for  silvering  by  weight  with  25  grammes  of  fine  silver 
as  silver  cyanide  and  25  grammes  of  99-percent  potassium 
cyanide,  and  a  current-density  of  0.3  ampere  per  square  deci- 
meter. Hence  the  current-output  of  the  bath  to  be  used  has 
to  be  determined,  and  the  weights  of  copper  corresponding  to 
the  silver  deposit  are  then  found  in  the  table  for  the  deter- 
mined current-output.  As  the  current-output  is  subject  to 
change  by  the  bath  becoming  gradually  contaminated  by  for- 
eign metals,  which  cannot  be  avoided  in  silvering  metals 
soluble  in  potassium  cyanide,  for  instance,  zinc  and  copper, 
it  will  be  necessary  to  determine  the  current-output  at  least 
twice  a  year. 

As  previously  mentioned,  the  current-output  is  materially 
smaller  when  the  bath  is  agitated  than  when  it  is  at  rest,  and 
hence  the  controlling  silver  bath  cannot  be  used  for  agitated 
baths  because,  in  order  to  obtain  accurate  weighing  results, 
agitation  of  the  controlling  bath  has  to  be  avoided.  In  this 
case  the  copper  solution  (see  p.  392)  has  also  to  be  used 
with  reference  to  the  tables  for  the  respective  current-output. 
However,  when  the  controlling  apparatus  works  with  the  cop- 
per solution,  it  still  has  the  advantage  of  no  current  passing 
through  sensitive  portions  of  the  balance,  and  thus  they  are 
not  subject  to  wear. 

Calculation  of  the  weight  of  the  silver  deposit  from  the  current- 
strength  used.  This  can  be  done  if  the  current  conducted  into 
the  bath  during  silvering  be  constantly  kept  at  the  same 
strength,  and  the  current-output  of  the  bath  be  taken  into 
consideration.  According  to  the  table  on  p.  61,  one  ampere 
deposits  in  1  hour  4.0248  grammes  of  silver,  hence  after  t 
hours  with  a  current-strength  i :  4.0248  X  i  X  t  grammes  of 
silver  will  be  deposited,  if  the  current-output  amounts  to  100. 
However,  the  latter  is,  as  a  rule,  only  98  to  99  per  cent.,  and 


DEPOSITION    OF    SILVER.  399' 

the  value  obtained  is  therefore  to  be  multiplied  by  the  frac- 
tion -n)-0-  or  -£fe,  in  order  to  determine  the  actual  weight  of  the 
deposit. 

Attention  must,  however,  be  drawn  to  the  fact  that  it  is- 
very  difficult  to  keep  the  current-strength  quite  constant  for  a 
longer  time,  especially  where  numerous  baths  are  connected 
to  a  common  circuit,  and  for  this  reason  a  calculation,  based 
upon  the  measurement  of  the  current-strength,  will  very  likely 
be  in  most  cases  impracticable. 

For  the  calculation  of  the  time  which  has  been  consumed 
for  depositing  a  certain  weight  of  silver  when  the  current- 
strength  is  known,  the  desired  weight  of  the  deposit  has  to  be 
divided  by  the  product  from  current-strength  times  chemical 
equivalent  of  the  silver,  and  the.  value  found  multiplied  by 


nr  ±0.0. 

U1       99- 


If,  for  instance,  50  grammes  of  silver  are  to  be  deposited 
upon  one  dozen  spoons,  and  the  current-strength  be  3.2: 
amperes  and  the  current-output  99  per  cent.,  the  time  is  found 
from  the  following  calculation  : 

50  X  100  5000 

_  =  3.92  hours  =  3  hours  55 


3.2  X  4.0248  X  99         1275.05 
minutes. 

If  the  current-strength  is  to  be  calculated,  which  is  required 
to  produce  in  a  given  time  a  determined  thickness  of  deposit, 
the  product  from  the  desired  thickness  in  millimeters,  times 
the  object-surface  in  square  decimeters,  times  the  specific 
gravity  of  the  metal  to  be  deposited,  times  1000,  has  to  be 
divided  by  the  product  from  time,  times  electro-chemical 
equivalent,  times  current-output.  Suppose,  for  instance,  the 
desired  thickness  of  the  deposit  is  to  be  0.1  millimeter,  the 
object-surface  1.5  square  decimeter,  the  specific  gravity  10.5, 
the  time  4  hours,  the  electro-chemical  equivalent  4.025,  and 
the  current-output  98  per  cent.,  then  the  current-strength 
required  is: 

0.1  X  1.5  X  10.0  X  100  1575 

4  X  4.02481058-     =  1677^2 


400  ELECTRO-DEPOSITION    OF    METALS. 

When  the  articles  have  received  a  deposit  of  the  required 
weight,  they  are  treated  for  the  prevention  of  subsequent  yel- 
lowing according  to  one  of  the  methods  given  on  p.  379,  then 
scratch-brushed  bright  with  the  use  of  decoction  of  soap-root, 
plunged  in  hot  water  and  dried  in  sawdust. 

Mat  silver. — Articles  which  are  to  retain  the  beautiful  crys- 
talline dead  white  with  which  they  come  from  the  bath  are, 
without  touching  them  with  the  fingers  or  knocking  them 
against  the  sides  of  the  vessel,  rinsed  thoroughly  in  clean 
water,  plunged  into  very  hot,  distilled  water,  and  then  sus- 
pended free  to  dry.  Immediately  after  drying  they  are  to  be 
provided  with  a  thin  coat  of  transparent  lacquer  to  protect  the 
dead-white  coating,  which  readily  turns  yellow,  and,  more- 
over, is  very  sensitive. 

Frosting  silver  is  affected  by  means  of  scratch-brushes.  They 
take  different  forms,  according  to  the  kind  of  work  to  be 
frosted.  They  are  made  of  several  strengths,  that  is,  the 
wires  of  them  are  especially  prepared  of  several  thicknesses, 
and  when  a  very  fine  satin  finish  is  required,  a  brush  of  very 
fine  wire  is  taken,  and  so  on.  A  brush  with  wires  thicker 
and  thicker  in  proportion  is  taken  as  a  more  extended  rough- 
ness is  desired.  These  wire  brushes  are  fixed  upon  a  hori- 
zontal spindle  in  the  lathe.  Frosting  requires  great  speed  to 
do  the  work  nicely.  The  wires  of  the  scratch-brush  must  be 
even  on  the  surface,  all  of  the  same  length,  and  always  kept 
straight  at  the  points,  otherwise  the  frosting  will  not  be 
regular.  Sometimes  the  little  hand  scratch-brushes  are 
employed  for  coarser  work;  four  of  them  are  taken,  and  firmly 
secured  in  four  corresponding  grooves  in  a  circular  chuck, 
which  screws  into  the  lathe.  The  ends  of  the  four  little 
brushes  are  repeated ly  cut  off  as  occasion  requires  in  order  to 
present  a  straight  surface  for  continual  contact  with  the  work, 
without  which  it  would  not  present  a  uniform  appearance. 

According  to  Gee,  the  following  mixture  may  also  be  used 
for  frosting  silver:  Sulphuric  acid  1  oz.,  water  1  oz.,  saltpetre 
2  dwts.  Add  the  sulphuric  acid  to  the  water  and  afterwards 


DEPOSITION    OF    SILVER.  401 

put  in  the  saltpetre  in  a  state  of  fine  powder.  The  mixture  is 
•used  in  the  boiling  state  and  takes  a  few  minutes  to  accom- 
plish the  desired  object. 

PoUshing  the  -deposits. — The  silvered  articles  having  been 
•scratch-brushed,  must  finally  be  polished,  which  may  be 
-effected  upon  a  fine  felt  wheel  with  the  use  of  rouge,  but  im- 
parting high  luster  by  burnishing  is  to  be  preferred,  the  de- 
posit being  first  treated  with  the  steel  burnisher,  and  then 
with  the  stone  burnisher,  as  explained  on  p.  216. 

In  some  establishments  in  which  plated  table-ware  in  large 
^quantity  is  turned  out,  ingeniously-devised  burnishing  ma- 
chines driven  by  power  are  in  use,  by  which  much  of  the 
manual  labor  is  saved.  The  knife,  spoon,  etc.,  each  supported 
by  its  tips  in  a  suitable  holder,  are  very  slowly  rotated,  while 
the  burnishing-tool  moves  quickly  over  the  surface,  perform- 
ing the  work  rapidly  and  satisfactorily. 

When  burnishing  is  completed,  the  surface  is  wiped  off  lon- 
gitudinally with  an  old,  soft  calico  rag.  Sawdust,  hard  cloth, 
>and  tissue  paper  produce  streaks. 

B.  Ordinary  silver-plating. — Objects  which  are  to  receive  a 
•deposit  of  less  thickness  have  to  undergo  exactly  the  same 
operations  described  under  plating  by  weight,  the  only  differ- 
ence being  that  for  quicking  a  weaker  solution  (15  to  31 
grains  of  nitrate  of  mercury  to  1  quart  of  water),  or  very 
•dilute  solution  of  potassium-mercury  cyanide  (77  grains  of 
potassium-mercury  cyanide  and  77  grains  of  potassium  cya- 
nide to  1  quart  of  water)  is  used,  and  that  the  objects  remain 
-a  shorter  time  in  the  bath. 

Direct  silvering  of  Britannia,  tin,  German  silver.  As  pre- 
viously mentioned,  iron,  steel,  zinc  and  tin  should  first  be 
coppered  or  brassed.  However,  tin  and  Britannia  may  also 
be  directly  plated,  but  the  bath  must  be  rich  in  silver  and 
contain  a  large  excess  of  potassium  cyanide.  Further,  the 
current  should  be  so  strong  that  the  articles  acquire  a  blue- 
gray  color.  They  are  then  suspended  in  the  silver  bath  of 
normal  composition,  and  plating  is  finished  with  a  normal 
current. 
26 


402  ELECTRO-DEPOSITION    OF    METALS. 

The  same  process  is  also  suitable  for  plating  articles  of  Ger- 
man silver  rich  in  nickel.  In  polishing  such  articles  it  is  fre- 
quently observed  that  the  deposit  rises,  but  by  plating  in  the 
above-mentioned  preparatory  bath,  and  finishing  in  the  nor- 
mal bath,  the  deposit  will  very  well  bear  polishing  with  the 
steel. 

For  silver-plating  Britannia  ware  and  articles  of  tin,  Gore 
recommends  the  following  process.  Boil  the  articles  in  caustic 
potash  solution,  scratch-brush  them,  and  plate  them  prepara- 
tively  with  a  strong  current  and  the  use  of  large  anode- 
surfaces  in  a  hot  silver  bath  (194°  F.),  and  then  finish  depo- 
sition to  the  desired  thickness  in  the  ordinary  cold  silver  bath. 

According  to  an  Australian  patent,  the  following  process  is 
claimed  to  yield  good  results  in  directly  silver-plating  iron  and 
steel :  The  article  to  be  plated  having  first  been  dipped  in  hot 
dilute  hydrochloric  acid  is  brought  into  solution  of  mercury 
nitrate  and  then  connected  with  the  zinc  pole  of  a  Bunsen 
element.  It  becomes  quickly  coated  with  a  la}^er  of  mercury, 
when  it  is  taken  out,  washed  and  brought  into  an  ordinary 
silver  bath.  When  covered  with  a  layer  of  silver  of  sufficient 
thickness,  it  is  heated  to  572°  F.,  the  mercury  evaporating  at 
this  temperature.  It  is  claimed  that  silver  deposited  in  this 
manner  adheres  more  firmly  than  by  any  other  process,  but 
it  is  doubtful  whether  for  solid  silver-plating  this  method  can 
replace  previous  coppering. 

Stopping  off.  If  certain  parts  of  a  metallic  article  are  not  to 
receive  a  deposit,  as  for  instance,  when  a  contrast  is  to  be 
effected  by  depositing  different  metals  upon  the  same  object, 
these  parts  are  covered,  or  "  stopped-off,"  with  a  varnish. 
Stopping-off  varnish  is  prepared  by  dissolving  asphalt  or  dam- 
mar with  an  addition  of  mastic  in  oil  of  turpentine.  Apply 
with  a  brush,  and  after  thoroughly  drying  the  articles  in  the 
drying-chamber,  place  them  for  an  hour  in  very  cold  water, 
whereby  the  varnish  hardens  completely.  After  plating,  the 
varnish  is  removed,  best  with  benzine,  the  articles  plunged  in 
hot  water  and  dried  in  sawdust. 


DEPOSITION    OF    SILVER.  403 

For  a  varnish  that  will  resist  the  solvent  power  of  the  hot 
alkaline  gilding  liquid,  Gore  recommends  the  following  com- 
position :  Translucent  rosin  10  parts,  yellow  beeswax  6,  extra- 
fine  red  sealing-wax  4,  finest  polishing  rouge  3. 

Quick-drying,  stopping-off  varnishes,  which  harden  imme- 
diately at  the  ordinary  temperature  and  resist  cyanide  baths, 
are  now  found  in  commerce. 

Special  applications  of  electro- silvering. — It  remains  to  men- 
tion a  few  special  applications  of  electro-silvering  as  well  as 
processes  of  decorating  with  silver  by  electrical  and  chemical 
means. 

Silvering  of  fine  copper  wire  is  effected  in  an  apparatus,  which 
is  described  and  illustrated  in  Chapter  IX,  "  Deposition  of 
Gold,"  where  further  details  will  be  found.  Luster  is  im- 
parted to  the  silvered  wire  by  drawing  through  a  draw-plate. 

Incrustations  with  silver  (and  gold,  and  other  metals). — By  in- 
crusting  is  understood  the  inlaying  of  depressions,  produced  by 
engraving  or  etching  upon  a  metallic  body,  with  silver,  gold 
and  other  metals,  such  as  Japanese  incrustations,  which  are 
made  by  mechanically  pressing  the  silver  or  gold  into  the  de- 
pressions. Such  incrustations,  however,  can  also  be  produced 
by  electro-deposition,  the  process  being  as  follows:  The  design 
which  is  to  be  incrusted  upon  a  metal  is  executed  with  a  pig- 
ment of  white-lead  and  glue-water  or  gum-water.  The  portion 
not  covered  by  the  design  is  then  coated  with  stopping-off 
varnish.  The  article  is  next  placed  in  dilute  nitric  acid, 
whereby  the  pigment  is  first  dissolved,  and  next  the  surface 
etched,  which  is  allowed  to  progress  to  a  certain  depth. 
Etching  being  finished,  the  article  is  washed  in  an  abundance 
of  water  and  immediately  brought  into  a  silver  or  gold  bath, 
in  which,  by  the  action  of  the  current,  the  exposed  places 
are  filled  up  with  metal.  This  being  done,  the  stopping-off 
varnish  is  removed  with  benzine,  the  surface  ground  smooth, 
and  polished.  In  this  manner  one  article  may  be  incrusted 
with  several  metals;  for  instance,  brass  may  be  incrusted  with 
copper,  silver  and  gold,  and  by  oxidizing  or  coloring  portions 


404  ELECTRO-DEPOSITION    OF    METALS. 

of  the  copper  beautiful  effects  can  be  produced.  The  prin- 
cipal requisites  for  these  incrustations  are  manual  skill  and 
•much  patience.  Expensive  apparatus  is  not  required,  every 
skilled  electro-plater  being  able  to  execute  the  work. 

Imitation  of  niel  or  nielled  silvering.  By  nielling  is  under- 
stood the  inlaying  of  designs  produced  either  by  engraving  or 
stamping,  with  a  black  mixture  of  metallic  sulphides.  The 
nielliug  powder  is  prepared  by  melting  silver  20  parts  by 
weight,  copper  90  parts  and  lead  150  parts.  To  the  liquid 
metallic  mass  add  26  J  ozs.  of  sulphur  and  }  oz.  of  ammonium 
•chloride,  quickly  cover  the  crucible  and  continue  heating  until 
the  excess  of  sulphur  is  volatilized.  Then  pour  the  contents 
of  the  crucible  into  another  crucible,  the  bottom  of  which  is 
covered  about  J  inch  deep  with  flowers  of  sulphur,  cover  the 
crucible  and  allow  the  mixture  to  cool.  When  cold  bring  the 
contents  once  more  to  the  fusing  point,  and  pour  the  fused 
mass  in  a  thin  stream  into  a  bucket  filled  with  water,  whereby 
granulated  metal  is  formed,  which  can  be  readily  reduced  in 
a  mortar  to  a  fine  powder.  This  powder  is  mixed  with  am- 
monium chloride  and  gum-water  to  a  thin  paste.  This  paste 
is  brought  into  the  designs  produced  by  engraving  or  stamp- 
ing, and  after  drying  burnt-in  in  a  muffle.  When  cold,  any 
roughness  is  removed  by  grinding,  and  after  polishing  a 
sharp,  black  design  in  white  silver  is  obtained. 

To  imitate  niel  by  electro-deposition,  the  design  is  executed 
upon  the  surface  with  a  pigment  consisting  of  white  lead  and 
glue-  or  gum-water.  The  portions  which  are  to  remain  free 
are  coated  with  stopping-off  varnish,  and  the  design  is  un- 
covered by  etching  with  very  dilute  nitric  acid.  The  article 
is  then  brought  as  the  anode  into  dilute  solution  of  ammonium 
sulphide,  while  a  small  sheet  of  platinum  connected  to  the 
negative  pole  is  dipped  into  the  solution.  Sulphide  of  silver 
being  formed,  the  design  becomes  rapidly  black-gray,  and 
after  removing  the  stopping-off  varnish  with  benzine,  stands 
out  in  sharp  contrast  from  the  white  silver. 

Upon    brass,   nielling    may   be   imitated    by   silvering   the 


DEPOSITIONS7    OF    SILVER.  405 

article  and  then  engraving  the  design,  by  which  the  silver 
is  removed  and  the  brass  uncovered.  The  article  is  then 
brought  into  the  black  bright-dip,  by  which  the  uncovered 
brass  is  colored  black  while  the  silvered  portions  remain  un- 
changed. If  portions  in  relief  are  to  be  made  black,  the  sil- 
vering is  removed  by  grinding,  the  article  dipped  into  cream 
of  tartar  solution,  and  then  brought  into  the  black  bright-dip. 
This  process  is  largely  employed  by  manufacturers  of  buttons 
when  silvered  buttons  are  to  be  supplied  with  the  name  of  the 
firm  and  the  quality  number  in  black. 

Old  (antique)  silvering. — To  give  silvered  articles  an  antique 
appearance  coat  them  with  a  thin  paste  of  6  parts  graphite,  1 
red  ochre  and  sufficient  spirits  of  turpentine.  After  drying, 
gentle  rubbing  with  a  soft  brush  removes  the  excess  of  powder, 
and  the  reliefs  are  set  off  (discharged)  by  means  of  a  rag 
dipped  into  alcohol. 

A  tone  resembling  antique  silvering  is  also  obtained  by 
brushing  the  silvered  articles  with  a  soft  brush  moistened  with 
very  dilute  alcoholic  solution  of  chloride  of  platinum. 

In  order  to  impart  the  old  silver  tinge  to  small  articles, 
such  as  buttons,  rings,  etc.,  they  are  agitated  in  the  above- 
mentioned  paste,  and  then  "  tumbled  "  with  a  large  quantity 
of  dry  sawdust  until  the  desired  shade  is  obtained. 

With  the  use  of  the  electric  current  and  carbon  anodes, 
antique  silver  may  be  produced  as  follows  :  Bring  the  silvered 
articles,  previously  thoroughly  freed  from  grease,  into  the 
silver  bath  at  an  electro-motive  force  of  4  to  5  volts,  and  allow 
them  to  remain  for  a  few  minutes  until  they  become  covered 
with  a  uniform  blue-gray  deposit.  They  are  then  thoroughly 
rinsed  in  water,  and  the  raised  portions  rubbed  with  very  fine 
pumice,  to  lay  bare  the  silver.  If  surfaces  are  to  appear  in 
antique  silver,  the  deposit  is  only  sufficiently  removed  with 
pumice  for  the  silver  to  shine  through,  and  the  surface  to 
show  the  proper  antique-silver  tone. 

Oxidized  silvering.  This  term  is  incorrect,  as  silver  oxide 
does  not  form  the  coloring  film  or  at  least  only  to  a  very 


406  ELECTRO-DEPOSITION    OF    METALS. 

slight  extent,  the  coloration  being  due  to  the  formation  of 
silver  sulphide  or  silver  chloride  upon  the  objects.  This  pro- 
cess of  coloring  silver  is  frequently  employed  to  obtain  dec- 
orative contrasts.  Solution  of  pentasulphide  of  potassium 
(liver  of  sulphur  of  the  shops)  is  generally  used  for  the  pur- 
pose. Dissolve  liver  of  sulphur  1  oz.,  and  ammonium  car- 
bonate 2  ozs.,  in  1  gallon  of  water  heated  to  176°  F.  Immerse 
the  objects  in  the  solution  and  allow  them  to  remain  until  they 
have  acquired  the  desired  dark  tone.  Immediately  after  im- 
mersion the  articles  become  pale  gray,  then  darker,  and 
finally  deep  black  blue.  For  coloring  in  this  manner,  the 
silvering  should  not  be  too  thin.  For  objects  with  a  very 
thick  deposit  of  silver,  solution  of  double  the  strength  may  be 
used.  Very  slightly  silvered  objects  cannot  be  colored  in  this 
manner,  as  the  bath  would  remove  the  silvering,  or  under  the 
most  favorable  conditions  produce  only  a  gray  color.  If  the 
operation  is  not  successful,  and  the  objects  come  from  the 
bath  stained  or  otherwise,  dip  them  in  warm  potassium 
cyanide  solution,  which  rapidly  dissolves  the  silver  sulphide 
formed. 

A  bath  which  produces  the  same  effect  as  potassium  sul- 
phide solution  may  be  cheaply  prepared  as  follows :  Pour  1 
quart  of  water  over  13  ozs.  of  unslaked  lime  and  22J  ozs. 
flowers  of  sulphur.  The  mixture  becomes  quickly  heated 
and  thick.  Dilute  it  with  1  quart  hot  water  and  boil  half  an 
hour.  The  resulting  liquor  is  now  ready  for  use  and  is  best 
employed  very  hot.  If,  whilst  boiling  the  solution,  1|  ozs.  of 
antimonious  sulphide  or  1}  ozs.  of  arsenious  sulphide  be  added, 
an  agreeable  bluish-gray  coloration  is  obtained  which,  with 
the  use  of  antimonious  sulphide  passes  later  on  into  a  beauti- 
ful gray-brown. 

A  beautiful  brown  tone  is  imparted  to  silver  objects  by  im- 
mersion in  the  following  solution  :  Copper  sulphate  10  ozs., 
saltpetre  5  ozs.,  ammonium  chloride  10  ozs. 

Another  process  is  as  follows :  Place  the  objects  in  a  porce- 
lain dish,  cover  them  with  ammonium  sulphide,  and  heat 


DEPOSITION    OF    SILVER.  407 

gradually.  When  the  objects  have  acquired  a  blue-black 
<?olor,  take  them  from  the  dish,  place  them  in  soap- water  and, 
so  long  as  they  remain  in  the  latter,  rub  them  with  a  soft 
brush. 

A  yellow  color  is  imparted  to  silvered  articles  by  immersion 
in  a  hot  saturated  solution  of  copper  chloride,  rinsing  and 
•drying. 

For  silvering  by  contact,  boiling  and  friction,  see  special  chap- 
ter "  Depositions  by  Contact." 

Stripping  silvered  articles. — When  a  silvering  operation  has 
failed,  or  the  silver  is  to  be  stripped  from  old  silvered  articles, 
different  methods  have  to  be  used  according  to  the  nature  of 
the  basis-metal.  Silvered  iron  articles  are  treated  as  the  anode 
in  potassium  cyanide  solution  in  water  (1  : 20),  the  iron  not 
being  attacked  by  potassium  cyanide.  As  cathode  suspend 
in  the  solution  a  few  silver  anodes  or  a  copper-sheet  rubbed 
with  an  oily  rag ;  the  silver  precipitates  upon  the  copper 
sheet  but  does  not  "adhere  to  it.  Articles,  the  basis  of  which 
is  copper,  are  best  stripped  by  immersion  in  a  mixture  of 
equal  parts  of  anhydrous  (fuming)  sulphuric  acid  and  nitric 
•acid  of  40°  Be.  This  mixture  makes  the  copper  passive,  it 
not  being  attacked  while  the  silver  is  dissolved.  Care  must, 
however,  be  had  not  to  introduce  any  water  into  the  acids, 
nor  to  let  them  stand  without  being  hermetically  closed,  since 
by  absorbing  moisture  from  the  air  they  become  dilute,  and 
may  then  exert  a  dissolving  effect  upon  the  copper.  The 
fuming  sulphuric  acid  may  also  be  highly  heated  in  a  shallow 
pan  of  ^enameled  cast  iron.  Then  at  the  moment  of  using  it 
pinches  of  dry  and  pulverized  nitrate  of  potassium  (saltpeter) 
are  thrown  into  it,  and  the  article,  held  with  copper  tongs,  is 
plunged  into  the  liquid.  The  silver  is  rapidly  dissolved, 
while  the  copper  or  its  alloys  is  but  slightly  corroded.  Ac- 
cording to  the  rapidity  of  the  progress  of  solution,  fresh  addi- 
tions of  saltpeter  are  made.  All  the  silver  has  been  dissolved 
when,  after  rinsing  in  water  and  dipping  the  articles  into  the 
•cleansing  acids,  they  present  no  brown  or  black  spots,  that  is 


408  ELECTRO-DEPOSITION    OF    METALS. 

to  say,  when  they  behave  like  new.  In  this  hot  acid  stripping 
proceeds  more  quickly  than  in  the  cold  acid  mixture,  but  the- 
latter  acts  more  uniformly. 

Determination  of  silver-plating. — By  applying  to  genuine- 
silver-plating  a  drop  of  nitric  acid  of  1.2  specific  gravity,  in 
which  red  chromate  of  potash  has  been  dissolved  to  satura- 
tion, a  red  stain  of  chromate  of  silver  is  formed.  According  to- 
Grager,  this  method  may  also  be  used,  to  a  certain  extent  for- 
the  recognition  of  any  other  white  metal  which  may  be  mis- 
taken for  silver.  A  drop  of  the  mixture  applied  to  German, 
silver  becomes  brown,  no  red  stain  appearing  after  rinsing 
with  water;  upon  Britannia  the  drop  produces  a  black  stain;. 
zinc  is  etched  without  a  colored  spot  remaining  behind  ;  upon 
amalgamated  metals  a  brownish  precipitate  is  formed,  which: 
does  not  adhere  and  is  washed  away  by  water;  upon  tin  the 
drop  also  acquires  a  brownish  color,  and  by  diluting  with, 
water  a  yellow  precipitate  is  formed  ;  upon  lead  a  beautiful  yel- 
low precipitate  is  formed. 

Custom-house  officers  in  Germany  are  directed  by  law  to 
use  the  following  process  for  the  determination  of  genuine  siK 
ver-plating  :  Wash  a  place  on  the  article  with  ether  or  alco- 
hol, dry  with  blotting  paper,  and  apply  to  the  spot  thus 
cleansed  a  drop  of  a  1  to  2  per  cent,  solution  of  crystallized  bi- 
sulphite of  soda  prepared  by  boiling  1.05  ozs.  of  sodium  sul- 
phite and  2.36  drachms  of  flowers  of  sulphur  with  0.88  oz. 
of  water  until  the  sulphur  is  dissolved,  and  diluting  to  1 
quart  of  fluid.  Allow  the  drop  to  remain  upon  the  article 
about  ten  minutes  and  then  rinse  off  with  water.  Upon  sil- 
ver articles,  a  full,  round,  steel-gray  spot  is  produced.  Other 
white  metals  and  alloys,  with  the  exception  of  amalgamated 
copper,  do  not  show  this  phenomenon,  there  appearing  at  the 
utmost  a  dark  ring  at  the  edge  of  the  drop.  Amalgamated 
copper  is  more  quickly  colored,  and  acquires  a  more  dead- 
black  color  than  silver. 


DEPOSITION    OF    SILVER.  409 

Examination  of  silver  baths. 

For  the  quantitative  examination  of  silver  baths,  the  deter- 
mination of  the  content  of  free  potassium  cyanide  and  of  me- 
tallic silver  as  well  as  of  the  potassium  carbonate  which  is 
formed  by  the  action  of  air,  etc.,  upon  the  potassium  cyanide, 
has  to  be  taken  into  consideration. 

Regarding  the  determination  of  the  free  potassium  cyanide, 
the  reader  is  referred  to  the  method  given  under  "  Examina- 
tion of  copper  baths  containing  potassium  cyanide,"  and  what 
has  been  said  there  in  reference  to  replacing  the  deficiency 
also  applies  here. 

The  potassium  carbonate  which  is  formed  in  constantly  in- 
creasing quantities  in  the  bath,  is  best  removed  by  the  ad- 
dition of  barium  cyanide  solution,  whereby,  in  consequence  of 
reciprocal  decomposition,  potassium  cyanide  is  formed,  while 
barium  carbonate  in  an  insoluble  state  is  separated. 

The  determination  of  the  potassium  carbonate  present  in  the 
bath  is  desirable,  so  as  to  be  able  on  the  one  hand,  to  calcu- 
late the  quantity  of  barium  cyanide  required  for  its  decompo- 
sition and,  on  the  other,  to  become  acquainted  with  the 
quantity  of  free  potassium  cyanide  formed  thereby. 

The  determination  of  the  potassium  carbonate  is  effected  as 
follows:  Bring  by  means  of  the  pipette,  20  cubic  centimeters 
of  silver  bath  into  a  beaker,  dilute  with  50  cubic  centimeters 
of  water,  and  compound  with  barium  nitrate  solution  in  ex- 
cess. Allow  to  settle  for  some  time,  then  filter  through  not 
too  large  a  paper  filter,  taking  care  that  the  entire  precipitate 
reaches  the  filter,  and  wash  the  filter  thoroughly  with  water 
until  a  few  drops  of  the  filtrate,  when  evaporated  upon  a 
platinum,  sheet,  leave  no  residue.  Now  take  the  filter,  to- 
gether with  the  residue,  carefully  from  the  funnel,  bring  it 
into  a  beaker,  and  add  water,  as  well  as  a  carefully  measured 
quantity  of  standard  nitric  acid,  which  should,  however,  be 
somewhat  larger  than  required  for  dissolving  the  barium  car- 
bonate. While  solution  is  being  effected,  keep  the  beaker 


410  ELECTRO-DEPOSITION    OF    METALS. 

-covered  with  a  watch  glass,  and  then  rinse  any  drops  appear- 
ing upon  the  latter  into  the  beaker  by  means  of  distilled 
water.  Add  to  the  solution,  as  an  indicator,  a  few  drops  of 
methyl-orange,  whereby  the  solution  is  colored  red,  and  add, 
while  stirring  constantly,  from  a  burette,  standard  soda  solu- 
tion until  the  red  color  of  the  solution  passes  into  yellow.  By 
now  deducting  the  cubic  centimeters  of  soda  solution  used 
from  the  cubic  centimeters  of  standard  nitric  acid  added  to 
the  solution  of  the  barium  carbonate,  and  multiplying  the 
number  of  the  remaining  cubic  centimeters  of  standard  nitric 
acid  by  3.45,  the  quantity  of  potassium  carbonate  in  grammes 
present  in  1  liter  of  silver  bath  is  obtained. 

Now  the  quantity  of  barium  cyanide  has  to  be  calculated, 
which  is  required  for  the  conversion  of  the  quantity  of  potas- 
sium carbonate  found,  into  potassium  cyanide  with  the  separa- 
tion of  barium  carbonate.     It  is  best  to  use  a  20  J  per  cent, 
barium  cyanide  solution,  and  since  1   gramme  of  potassium 
•carbonate  requires  for  conversion   1.36  grammes  of  barium 
•cyanide,  6.80  grammes  of  20  per  cent,  barium  cyanide  solution 
are  necessary  for  the  purpose,  and  each  gramme  of  potassium 
••carbonate  yields  0.942  gramme  of  potassium  cyanide.     Hence 
for  the  determination  of  the  potassium  cyanide  present  after 
the  destruction  of  the  potassium  carbonate,  there  has  to  be 
added  to  the  potassium  cyanide  found  by  titration,  the  content 
•of  free  potassium  cyanide  calculated  from  the  conversion  with 
barium  cyanide.     If  this  shows  a  deficit  as  compared  with  the 
original   content,  it  is  to  be  made  up  by  adding  only  about 
-one-half  the  quantity,  for  the  same  reason  as  given  in  speak- 
ing of  the  copper  bath,  namely,  because  the  potassium  for- 
•mate,  which  is  at  the  same  time  formed,  performs  the  function 
•of  the  potassium  cyanide. 

To  save  calculation  a  table  by  Steinach  and  Buchner  for 
use  of  a  20J  per  cent,  barium  cyanide  solution  is  here 


DEPOSITION    OF    SILVER. 


411 


For  1  liter  of  silver  bath  have  to  be  added 

Potassium  carbonate  in 
1  liter  of  silver  bath. 

20£  per  cent,  barium  cya- 

Potassium cyanide 

nide  solution. 

formed  thereby. 

1  gramme 

6.7  grammes 

0.95  gramme 

2 

13.4 

t 

1.90 

3 

20.1 

2.85 

4 

26.8 

3.80 

5 

33.5 

4.70 

6 

40.2 

5.70 

7 

46.9 

6.65 

8 

53.6 

7.60 

9 

60.3 

8.55 

10 

67.0 

9.50 

11 

73.7 

10.40 

12 

80.4 

11.40 

13 

87.1 

12.35 

14 

93.9 

13.30 

*     15 

100.5 

14.20 

For  the  determination  of  the  silver,  the  electrolytic  method  is 
the  most  simple  and  suitable  in  so  far  as  the  silver  bath  can 
be  directly  used  for  the  purpose. 

Bring  by  means  of  the  pipette  into  the  platinum  dish  10 
^cubic  centimeters  of  the  silver  bath,  or  20  cubic  centimeters 
if  the  bath  is  weak  ;  add,  according  to  the  greater  or  smaller 
•excess  of  the  potassium  cyanide  present,  J  to  1  gramme  of 
potassium  cyanide  dissolved  in  water,  and  dilute  up  to  1  or  1 J 
centimeters  from  the  edge  of  the  dish.  Heat,  by  means  of  a 
small  flame,  the  contents  of  the  dish  to  from  140°  to  149°  F., 
.and  maintain  this  temperature  as  nearly  constant  as  possible. 
Electrolysis  is  effected  with  a  current-density  ND  100  =  0.08 
ampere.  Complete  precipitation,  which  requires  3  to  3J 
hours,  is  recognized  by  ammonium  sulphide  producing  no 
•dark  coloration  of  the  fluid.  The  dish  is  then  washed,  with- 
•out  interrupting  the  current,  rinsed  ^th  alcohol  and  ether, 
dried  for  a  short  time  at  212°  F.,  and  weighed.  The  weight 
of  the  precipitate  multiplied  by  100  gives  the  content  of  silver 
in  grammes  per  liter  of  bath.  If  20  cubic  centimeters  of  silver 
bath  have  been  electrolyzed,  multiply  only  by  50. 


412  ELECTRO-DEPOSITION    OF    METALS. 

If  the  analysis  has  shown  a  deficit  of  silver  in  the  bath,  it 
can  be  readily  replaced.  For  strengthening  the  bath  it  is  best 
to  use  pure  crystallized  potassium-silver  cyanide,  which  in 
round  numbers  contains  50  per  cent,  of  silver.  Suppose  the 
bath  contains  per  liter  2  grammes  of  silver  less  than  it  should, 
then  for  each  liter  of  bath  (52  :  100  =  2  :  x  ;  x  =  3.8  grammes), 
3.8  grammes  of  pure  crystallized  potassium-silver  cyanide  have 
to  be  added. 

The  more  troublesome  volumetric  analysis  may  be  omitted,, 
it  offering  no  advantage  over  the  electrolytic  method. 

Recovery  of  silver  from  old  silver  baths,  etc. — Old  solutions 
which  contain  silver  in  the  form  of  a  silver  salt  are  easily 
treated.  It  is  sufficient  to  add  to  them,  in  excess,  a  solution 
of  common  salt,  or  hydrochloric  acid,  when  all  the  sijver 
will  be  precipitated  in  the  state  of  chloride  of  silver,  whichr 
after  washing,  may  be  employed  for  the  preparation  of  new 
baths. 

For  the  recovery  of  silver  from  solutions  which  contain  it  as 
cyanide,  the  solutions  may  be  evaporated  to  dry  ness,  the  resi- 
due mixed  with  a  small  quantity  of  calcined  soda  arid  potas- 
sium cyanide,  and  fused  in  a  crucible,  whereby  metallic  silver 
is  formed,  which,  when  the  heat  is  sufficiently  increased,  will 
be  found  as  a  button  upon  the  bottom  of  the  crucible  ;  or  if  it 
is  not  desirable  to  heat  to  the  melting-point  of  silver,  the 
fritted  mass  is  dissolved  in  hot  water,  and  the  solution  con- 
taining the  soda  and  cyanide  quickly  filtered  off  from  the 
metallic  silver.  The  evaporation  of  large  quantities  of  fluid, 
to  be  sure,  is  inconvenient,  and  requires  considerable  time. 
But  the  reducing  process  above  described  is  without  doubt  the 
most  simple  and  least  injurious. 

According  to  the  wet  method,  the  bath  is  strongly  acidulated 
with  hydrochloric  aci<j,  provision  being  made  for  the  effectual 
carrying-off  of  the  hydrochloric  acid  liberated.  Remove  the 
precipitated  chloride  of  silver  and  cyanide  of  copper  by  filtra- 
tion, and,  after  thorough  washing,  transfer  it  to  a  porcelain 
dish  and  treat  it,  with  the  aid  of  heat,  with  hot  hydrochloric 


DEPOSITION    OF    SILVER.  413 

:acid,  which  will  dissolve  the  cyanide  of  copper.  The  result- 
ing chloride  of  silver  is  then  reduced  to  the  metallic  state  by 
inixing  it  with  four  times  its  weight  of  crystallized  carbonate 
of  soda,  and  half  its  weight  of  pulverized  charcoal.  The  whole 
is  made, into  a  homogeneous  paste,  which  is  thoroughly  dried, 
and  then  introduced  into  a  strongly-heated  crucible.  When 
all  the  material  has  been  introduced,  the  heat  is  raised  to  pro- 
mote complete  fusion  and  to  facilitate  the  collection  of  the 
separate  globules  of  silver  into  a  single  button  at  the  bottom 
of  the  crucible,  where  it  will  be  found  after  cooling.  If  gran- 
ulated silver  is  wanted,  pour  the  metal  in  a  thin  stream  and 
from  a  certain  height,  into  a  large  volume  of  water. 

A  very  simple  method  is  as  follows  :  Bring  the  silver  bath 
into  flasks,  mix  the  contents  of  the  flask  with  zinc  dust  (zinc 
in  a  finely-divided  state)  in  the  proportion  of  about  J  oz.  per 
quart  of  bath,  and  shake  thoroughly  5  or  6  times  every  day. 
In  five  days  all  the  silver  is  precipitated.  Decant  the  clear 
liquid  from  the  precipitate,  wash  the  latter  several  times  with 
water,  and  dissolve  the  zinc  contained  in  the  precipitate  in 
pure  hydrochloric  acid.  The  silver  remains  behind  in  a  pul- 
verulent form,  and  may  be  dissolved  in  nitric  acid,  and  worked 
up  into  silver  chloride  or  silver  cyanide.  In  place  of  zinc, 
aluminium  powder  may  be  used  for  precipitation,  the  excess 
of  aluminium  being  then  dissolved  by  caustic  potash,  or 
caustic  soda  solution. 

From  acid  mixtures  used  for  stripping,  the  silver  may  be 
obtained  as  follows  :  Dilute  the  acid  mixture  with  10  to  20 
times  the  quantity  of  water,  and  precipitate  the  silver  as 
chloride  of  silver  by  means  of  hydrochloric  acid.  Interrupt 
the  addition  of  hydrochloric  acid,  when  a  drop  of  it  produces 
no  more  precipitate  of  chloride  of  silver  in  the  clear  fluid. 
The  precipitated  chloride  of  silver  is  filtered  off,  washed,  and 
either  directly  dissolved  in  potassium  cyanide,  or  the  silver  is 
regained  as  metal  by  fusing  the  chloride  of  silver  with  cal- 
•cined  soda  and  wood  charcoal  powder,  previously  thoroughly 
mixed. 


414  ELECTRO-DEPOSITION    OF    METALS. 

Still  more  simple  is  the  reduction  of  the  chloride  of  silver 
by  pure  zinc.  For  this  purpose  suspend  the  chloride  of  silver- 
by  water,  add  hydrochloric  acid,  and  place  pure  zinc  rods  or 
granulated  zinc  in  the  fluid.  While  zinc  dissolves,  metallic- 
silver  is  separated,  which  is  filtered  off,  washed  and  dried. 


CHAPTER  IX. 

DEPOSITION    OF    GOLD. 

GOLD  (Au  =  197.2  parts  by  weight)  is  generally  found  in- 
the  metallic  state.  It  is  one  of  the  metals  possessing  a  yellow 
color.  Precipitated  from  its  solution  with  green  vitriol  (fer- 
rous sulphate)  or  oxalic  acid,  it  appears  as  a  brown  powder 
without  luster,  which  on  pressing  with  the  burnisher  acquires 
the  color  and  luster  of  fused  gold.  Pure  gold  is  nearly  as  soft 
as  lead,  but  possesses  considerable  tenacity.  In  order  to  in- 
crease the  hardness  when  used  for  articles  of  jewelry  and  for 
coinage,  it  is  alloyed  with  silver  or  copper.  The  "fineness  of 
gold,"  or  its  proportion  in  the  alloy,  is  usually  expressed  by 
stating  the  number  of  carats  present  in  24  carats  of  the  mix- 
ture. Pure  gold  is  stated  to  be  24  carats  "fine;  "  standard 
gold  is  22  carats  fine;  18  carat  gold  is  a  mixture  of  18  parts 
of  gold  and  6  of  alloy.  Gold  is  the  most  malleable  and  duc- 
tile of  the  metals.  It  may  be  beaten  out  into  leaves  not  ex- 
ceeding To;Wo  °f  a  millimeter  in  thickness.  When  beaten 
out  into  thin  leaves  and  viewed  by  transmitted  light,  gold 
appears  green;  when  very  finely  divided  it  is  dark  red  or 
black.  The  specific  gravity  of  fused  gold  is  19.35,  and  that 
of  precipitated  gold  powder,  from  19.8  to  20.2.  Pure  gold 
melts  at  about  2016°  F.,  and  in  fusing  exhibits  a  sea  green 
color.  The  melting-points  of  alloyed  gold  vary  according  to 
the  degree  of  fineness.  Thus,  23  carat  gold  melts  at  2012°  F.; 
22  carat  at  2009°  ;  20  carat  at  2002°  ;  18  carat  at  1995°  ;  15 
carat  at  1992°;  13  carat  at  1990°;  12  carat  at  1987°;  10  carat 
at  1982°;  9  carat  at  1979°;  8  carat  at  1973°;  7  carat  at 
I9600.  The  fineness  of  gold  may  be  approximately  estimated 
by  means  of  the  touch-stone,  a  basaltic  stone  formerly  obtained 

(415) 


416  ELECTRO-DEPOSITION    OF    METALS. 

from  Asia  Minor,  but  now  procured  from  Saxony  and 
Bohemia.  The  sample  of  gold  to  be  tested  is  drawn  across 
the  stone,  and  the  streak  of  metal  is  treated  with  dilute  nitric 
acid.  From  the  rapidity  of  the  action  and  the  intensity  of 
the  green  color  produced — due  to  the  solution  of  the  copper,  as 
compared  with  streaks  made  by  alloys  of  known  composition 
— the  assay er  is  enabled  to  judge  of  the  proportion  of  inferior 
metal  which  is  present.  Gold  preserves  its  luster  in  the  air, 
and  is  not  acted  upon  by  any  of  the  ordinary  acids.  Nitric, 
hydrochloric,  or  sulphuric  acid  by  itself  does  not  dissolve 
gold,  but  it  dissolves  in  an  acid  mixture  which  develops 
chlorine,  hence  in  aqua  regia  (nitro-hydrochloric  acid). 

The  gold  found  in  commerce  under  the  name  of  shell-gold 
or  painter's  gold,  which  is  used  in  painting  and  for  repairing 
smaller  defects  in  electro-gilding,  is  prepared  by  triturating 
waste  in  the  manufacture  of  leaf  gold  with  water,  diluted 
honey,  or  gum- water.  Gold  solution  may  also  be  precipitated 
with  antimonic  chloride.  The  resulting  precipitate  is  tritu- 
rated with  barium  hydrate,  extracted  with  hydrochloric  acid, 
and  after  washing,  the  gold  powder  is  triturated  with  gum 
arabic  solution. 

Gold  baths.  Gold-plating  may  be  effected  in  a  hot  or  cold 
bath,  large  objects  being  generally  plated  in  the  latter,  and 
smaller  objects  in  the  former.  The  hot  bath  has  the  advantage 
of  requiring  less  current-strength,  besides  yielding  deposits  of 
greater  density  and  uniformity,  and  of  sadder,  richer  tones. 
Hot  baths  work  with  a  moderate  content  of  gold — 11 J  to  12J- 
grains  per  quart  of  bath — while  cold  baths  should  contain  not 
less  than  54  grains  per  quart. 

Baths  prepared  with  potassium  ferrocyanide  are  preferred 
by  some  authors,  while  others  work  with  a  solution  of  gold 
salt  and  potassium  bicarbonate,  and  others  recommend  a  so- 
lution of  cyanide  of  gold  in  potassium  cyanide.  With  proper 
treatment  of  the  bath,  good  results  may  be  obtained  with  either. 
However,  the  use  of  baths  prepared  with  potassium  ferrocy- 
anide cannot  be  recommended  on  account  of  the  secondary 


DEPOSITION    OF    GOLD.  417 

Decompositions  which  take  place  during  the  operation  of  plat- 
ing, and  because  the  baths  do  not  dissolve  the  gold  anodes. 
Below  only  approved  formulas  for  the  preparation  of  gold 
baths  will  be  given. 

I.  Bath  for  cold  gilding. — Fine  gold  in  the  form  of  fulmi- 
nating gold  54  grains,  98  per  cent,  potassium  cyandide  0.35 
to  0.5  oz.  (according  to  the  current-strength  used),  water  1 
quart. 

Electro-motive  force  at  10  cm.  electrode-distance,  and  with, 
the  use  of  0.35  oz.  of  potassium  cyanide,  1.35  volts ;  with  the 
iuse  of  0.5  oz.  of  potassium  cyanide,  1.2  volts. 

Current-density,  0.15  ampere. 

To  prepare  this  bath,  dissolve  54  grains  of  fine  gold  in  aqua 
regia  in  a  porcelain  dish  heated  over  a  gas  or  alcohol  flame, 
and  evaporate  the  solution  to  dryness.  Continue  the  heating 
until  the  solution  is  thickly-fluid  and  dark  brown,  and  on 
cooling  congeals  to  a  dark  brown  mass.  Heating  too  strongly 
should  be  avoided,  as  this  would  cause  decomposition  and  the 
auric  chloride  would  be  converted  into  aurous  chloride,  and 
•eventually  into  metallic  gold  and  chlorine,  which  escapes. 
The  neutral  chloride  of  gold  formed  in  this  manner  is  dissolved 
in  1  pint  of  water  and  ammonia  added  to  the  solution  so  long 
as  a  yellow-brown  precipitate  is  formed,  avoiding,  however, 
a  considerable  excess  of  ammonia.  The  precipitate  of  fulmi- 
nating gold  is  filtered  off,  washed,  and  dissolved  in  1  quart 
of  water  containing  0.5  oz.  of  potassium  cyanide  in  solution. 
The  solution  is  boiled,  replacing  the  water  lost  by  evaporation, 
until  the  odor  of  ammonia  which  is  liberated  by  dissolving 
the  fulminating  gold  in  potassium  cyanide  disappears,  when 
it  is  filtered.  Instead  of  dissolving  the  gold  and  preparing 
neutral  chloride  of  gold  by  evaporating,  it  is  more  convenient 
to  use  108  grains  of  chemically  pure  neutral  chloride  of  gold 
as  furnished  by  chemical  works,  and  precipitate  the  fulminat- 
ing gold  from  its  solution. 

Too  large  an  excess  of  potassium  cyanide  yields  gold  de- 
posits of  an  ugly,  pale  color.     When  working  with  a  more 
27 


418  ELECTRO-DEPOSITION    OF    METALS. 

powerful  current,  the  excess  of  potassium  cyanide  need  only 
be  slight ;  with  a  weaker  current  it  may  be  larger. 

The  fulminating  gold  must  not  be  dried,  as  in  this  condi- 
tion it  is  highly  explosive,  but  should  be  immediately  dis- 
solved while  in  a  moist  state. 

If  the  cost  of  a  bath  for  cold  gilding  with  such  a  high  con- 
tent of  gold  as  given  in  formula  I  should  appear  too  great,, 
only  27  grains  of  gold  per  quart  may  be  used.  With  a  suit- 
able electro-motive  force,  deposits  of  a  beautiful,  sad-yellow 
color  are  thus  also  obtained.  Such  a  bath  is  yielded  by  the- 
following  formula  : 

la.  Fine  gold  in  the  form  of  neutral  gold  chloride  27  grains^ 
98  to  99  per  cent,  potassium  cyanide  0.26  oz.,  water  1  quart. 

Electro-motive  force  at  10  cm.  electrode-distance,  2.0  volts. 

Current-density,  0.15  ampere. 

For  cold  gilding,  Roseleur  recommends  the  following  bath  : 

II.  Fine  gold  as  neutral  chloride  of  gold,  0.35  oz.;  98  per 
cent,  potassium  cyanide,  0.7  oz.;  water,  1  quart. 

Electro-motive  force  at  10  cm.  electrode-distance,  about  1.5* 
volts. 

Current-density,  0.12  ampere. 

Dissolve  the  gold-salt  from  0.35  oz.  of  fine  gold  or  about 
0.7  oz.  of  neutral  chloride  of  gold  in  J  pint  of  the  water,  and 
the  potassium  cyanide  in  the  other  J  pint  of  water,  and  after 
mixing  the  solutions  boil  for  half  an  hour.  The  preparation 
of  this  bath  is  more  simple  than  that  of  formula  I,  but  the- 
color  of  the  gold  deposit  obtained  with  the  latter  is  warmer 
and  sadder.  The  high  content  of  gold  in  the  bath,  prepared- 
according  to  formula  II,  readily  causes  a  red-brown  gold 
deposit,  and  hence  special  attention  has  to  be  paid  to  the 
regulation  of  the  current. 

For  those  who  prefer  gold  baths  prepared  with  yellow  prus- 
siate  of  potash  instead  of  potassium  cyanide,  the  following 
formula  for  cold-gilding  is  given  : 

III.  Yellow  prussiate  of  potash  (potassium  ferrocyanide), 
0.5  oz.;  carbonate  of  soda,  0.5  oz.;  fine  gold  (as  chloride  of 
gold  or  fulminating  gold),  30.75  grains;  water,  1  quart. 


DEPOSITION    OF    GOLD.  419 

Electro-motive  force  at  10  cm.  electrode-distance,  2  volts. 

Current-density,  0.15  ampere. 

To  prepare  the  bath,  heat  the  solutions  of  the  yellow  prus- 
siate  of  potash  and  of  the  carbonate  of  soda  in  the  water  to  the 
boiling-point,  add  the  gold-salt,  and  boil  J  hour,  or  with  use 
of  freshly-precipitated  fulminating  gold,  until  the  odor  of  am- 
monia disappears.  After  cooling,  the  solution  is  mixed  with  a 
quantity  of  distilled  water,  corresponding  to  the  water  lost  by 
evaporation,  and  filtered.  This  bath  gives  a  beautiful  bright 
gilding  upon  all  metals,  even  upon  iron  and  steel. 

The  yellow  prussiate  of  potash  baths  are  deservedly  popular 
for  decorative  gilding,  when  gold  deposits  of  different  colors 
are  to  be  produced  upon  an  object.  Certain  portions  have 
then  to  be  covered  with  stopping-off  varnish,  the  latter  being 
less  attacked  by  this  bath  than  by  one  containing  an  excess 
of  potassium  cyanide. 

This  bath  is  especially  suitable  for  the  so-called  clock  gild- 
ing. The  articles  are  first  provided  with  a  heavy  deposit  of 
copper  in  the  alkaline  copper  bath,  then  matt-coppered  in  the 
acid  copper  bath,  next  drawn  through  the  bright-pickling 
bath,  thoroughly  rinsed;  and  finally  gilded  in  the  bath  heated 
to  about  122°  F. 

Gold  baths  for  hot  gilding. — IV.  Fine  gold  (as  fulminating 
gold)  15.4  grains,  98  per  cent,  potassium  cyanide  77  grains, 
water  1  quart. 

Electro-motive  force  at  10  cm.  electrode-distance,  1.0  volt. 

Current- density,  0.1  ampere. 

This  bath  is  prepared  in  the  same  manner  as  that  according 
to  formula  I,  from  15.4  grains  of  fine  gold,  which  is  converted 
into  neutral  chloride  of  gold  by  dissolving  in  aqua  regia  arid 
evaporating ;  or  dissolve  directly  29.32  to  30.75  grains  of 
chemically  pure  neutral  chloride  of  gold  in  water,  precipitate 
the  gold  as  fulminating  gold  with  aqua  ammonia,  wash  the 
precipitate,  dissolve  it  in  water  containing  the  potassium  cya- 
nide, and  heat  until  the  odor  of  ammonia  disappears,  replac- 
ing the  water  lost  by  evaporation.  This  bath  yields  a  beau- 


420  ELECTRO-DEPOSITION    OF    METALS. 

tiful  sad  gilding  of  great  warmth.  All  that  has  been  said  in 
regard  to  the  content  of  potassium  cyanide  in  the  bath  pre- 
pared according  to  formula  I  also  applies  to  this  bath.  The 
temperature  should  be  between  158°  and  176°  F.,  and  the 
current-strength  2.0  to  2.5  volts. 

Roseleur  recommends  for  hot  gilding  : 

V.  Chemically  pure  crystallized  sodium  phosphate  2.11  ozs., 
neutral  sodium  sulphite  0.35  oz.,  potassium  cyanide  30.86 
grains,  fine  gold  (as  chloride)  15.43  grains,  distilled  water  1 
quart. 

Electro-motive  force  at  10  cm.  electrode  distance  1.5  volts. 

Current- density,  0.12  ampere. 

If  this  bath  is  to  serve  for  directly  plating  steel,  only  half 
the  quantity  of  potassium  cyanide  is  to  be  used,  and  the  ob- 
jects should  be  covered  with  the  use  of  a  somewhat  greater 
electro-motive  force.  Increasing  the  content  of  neutral  sodium 
sulphite  to  0.5  or  0.7  oz.  also  appears  advisable. 

Dissolve  in  a  porcelain  dish,  with  the  aid  of  moderate  heat, 
the  sodium  phosphate  and  sodium  sulphite,  and  when  the 
solution  is  cold,  add  the  neutral  chloride  of  gold  prepared 
from  15.43  grains  of  gold  =  about  30.86  grains  of  commercial 
chloride  of  gold,  and  the  potassium  cyanide.  For  use,  heat 
the  bath  to  between  158°  and  167°  F. 

For  the  preparation  of  gold  baths  for  hot  and   cold  gild-, 
ing,  double  gold  salts  and  triple  gold  salts,  as  well  as  gold 
solutions,  as  brought  into  commerce  by  some  manufacturers 
may  also  be  used. 

Many  gold-platers  prepare  their  gold  baths  with  the  assist- 
ance of  the  electric  current.  For  this  purpose  prepare  a  solu- 
tion of  3.52  ozs.  potassium  cyanide  (98  to  99  per  cent.)  per 
quart  of  water  and,  after  heating  to  between  122°  and  140°  F., 
conduct  the  current  of  two  Bunsen  cells  through  two  sheets  of 
gold,  not  too  small,  which  are  suspended  as  electrodes  in  the 
potassium  cyanide  solution.  The  action  of  the  current  is 
interrupted  when  the  solution  is  so  far  saturated  with  gold  that 
an  article  immersed  in  it  and  connected  to  the  negative  pole 


DEPOSITION    OF    GOLD.  421 

in  place  of  the  other  gold  sheet,  is  gilded  with  a  beautiful 
warm  tone.  By  weighing  the  sheet  of  gold  serving  as  anode, 
the  amount  of  gold  which  has  passed  into  the  solution  is 
ascertained.  According  to  English  authorities,  a  good  gold 
bath  prepared  according  to  this  method  should  contain  3.52 
ozs.  of  potassium  cyanide  and  0.7  oz.  of  fine  gold  per  quart  of 
water. 

The  only  advantage  of  this  mode  of  preparing  the  bath  is 
that  it  excludes  a  possible  loss  of  gold,  which  may  occur  in 
dissolving  gold,  evaporating  the  gold  solution,  etc.,  by  break- 
ing the  vessel  containing  the  solution.  However,  by  using 
commercial  chemically  pure  chloride  of  gold  such  loss  is 
avoided,  and  the  bath  prepared  according  to  the  formulae 
given  yields  richer  tones  than  a  gold  bath  produced  by  electro- 
lysis. Besides,  the  preparation  of  the  gold  bath  with  the 
assistance  of  the  electric  current  can  only  be  considered  for 
smaller  baths,  since  the  saturation  of  a  larger  volume  of  potas- 
sium cyanide  solution  requires  considerable  time,  and  the 
potassium  cyanide  is  strongly  decomposed  by  long  heating. 

Gold  anodes.  Management  of  gold  baths. — It  is  advisable  to 
keep  the  content  of  gold  in  the  baths  prepared  according  to 
the  different  formulae  as  constant  as  possible,  which  is  best 
effected  by  the  use  of  fine  gold  anodes. 

Insoluble  platinum  anodes  are  better  liked  in  gilding  than 
for  all  other  electro-plating  processes,  partly  because  they  are 
somewhat  cheaper,  and  partly  because  they  are  recommended 
in  most  books  on  the  subject.  However,  a  bath  which  has 
become  low  in  gold  does  not  yield  a  beautiful  gold  color,  and 
has  to  be  frequently  strengthened  by  the  addition  of  chloride 
of  gold  or  concentrated  solution  of  fulminating  gold  in  potas- 
sium cyanide,  the  preparation  of  which  consumes  time  and 
causes  expense,  so  that  the  use  of  gold  anodes  is  the  cheapest 
in  the  end,  especially  with  the  present  high  price  of  platinum. 

The  use  of  steel  anodes  for  cold  and  warm  cyanide  gold 
baths,  advocated  by  some,  cannot  be  recommended.  Every 
gilder  knows  from  experience  that,  when  the  enamel  of  the 


422  ELECTRO-DEPOSITION    OF    METALS. 

tanks  containing  the  gold  baths  becomes  defective,  the  baths 
in  a  short  time  fail.  The  reason  for  this  is  simply  that  the 
iron  on  the  defective  places  of  the  tank  decomposes  the  gold 
-bath,  metallic  gold  being  reduced.  Iron,  in  this  respect,  acts 
like  zinc,  which,  in  a  still  shorter  time,  precipitates  metallic 
gold  from  gold  baths.  Now,  when  iron  anodes  remain  sus- 
pended in  the  baths,  a  reduction  of  gold  takes  place,  while  a 
quantity  of  iron  equivalent  to  the  reduced  gold  is  dissolved, 
and,  in  the  form  of  ferric  oxide,  falls  to  the  bottom  of  the  vat. 

In  hot  gold  baths  this  separation  of  gold  proceeds  still  more 
rapidly  and  the  content  of  potassium  cyanide  in  the  bath  is 
destroyed,  yellow  prussiate  of  potash  being  formed.  The 
argument  made  in  favor*  of  the  use  of  steel  anodes,  that  the 
old  practitioners  often  added  intentionally  yellow  prussiate  of 
potash  to  their  baths  to  heighten  the  gold  tone  is  fallacious. 
A  plater  who  works  with  gold  baths  prepared  with  yellow 
prussiate  of  potash  cannot  expect  to  replace  the  gold  by  the 
solution  of  the  gold  anodes,  and  when  working  with  gold 
cyanide  and  potassium  cyanide  baths  there  is  no  inducement 
for  gradually  changing  the  bath  into  a  yellow  prussiate  of 
potash  bath  by  the  use  of  steel  anodes. 

According  to  one  statement,  a  hot  gold  bath  with  steel 
anodes  showed,  after  being  electrolyzed  for  70  hours,  scarcely 
a  trace  of  iron.  To  ascertain  the  correctness  of  this  statement 
by  an  experiment,  a  gold  bath  prepared  according  to  formula 
IV  was  electrolyzed  at  158°  F.,  with  a  blue  annealed  steel 
anode  weighing  12.092  grammes.  During  the  first  two  hours 
only  a  moderate  yellow-reddish  bloom  of  iron  salt  was  per- 
ceptible on  the  anode,  which  became  detached  from  the  latter 
and  fell  to  the  bottom  of  the  beaker.  The  bloom,  however, 
became  gradually  heavier,  the  bottom  of  the  beaker  was 
covered  with  a  precipitate  of  a  yellow-brown  color,  the  pre- 
viously colorless  bath  acquiring  a  yellow  color  and  after  elec- 
trolyzing  for  five  hours,  the  blue  color  of  the  anode  had  largely 
disappeared.  The  anode  weighed  now  11.832  grammes,  and 
had  consequently  lost  2.2  per  cent.  After  again  suspending 


DEPOSITION    OF    GOLD.  423 

it  in  the  bath  it  was  more  rapidly  attacked  in  consequence  of 
the  destruction  of  the  blue  annealing  color,  which  retarded 
'corrosion.  After  five  more  hours  the  anode  weighed  11.105 
grammes,  the  loss  being  therefore  8.16  per  cent.  The  bath 
now  showed  a  deep  yellow  color,  and  the  precipitate  on  the 
bottom  of  the  beaker  had  increased,  while  small,  lighter  flakes 
of  ferric  hydrate  spun  around  in  the  bath  and  attached  them- 
selves to  the  anode.  Electrolysis  was  now  discontinued,  since 
the  last  mentioned  phenomena  proved  the  uselessness  of  steel 
anodes  for  the  reasons  given  under  "  Deposition  of  Nickel  and 
Cobalt." 

As  regards  the  advantage  claimed  for  the  use  of  steel 
anodes,  that  a  large  anode-surface  corresponding  to  the  object- 
-surface  can  be  rendered  effective  without  taxing  too  severely 
the  pocket-book  of  the  gilder,  it  may  be  said  that  the  same 
object  can  in  a  more  rational  manner  be  attained  by  employ- 
ing carbon  anodes,  which  to  prevent  contamination  of  the 
!bath  by  particles  of  carbon,  are  placed  in  linen  bags.  Crosses 
and  balls  of  unusually  large  dimensions  for  church  towers 
'have  frequently  been  gilded  in  Dr.  Geo.  Langbein  &  Co.'s 
•establishment,  for  which  a  large  anode-surface  was  required 
in  order  to  obtain  a  uniformly  heavy  deposit,  and  in  such 
•oases  carbon  anodes  of  the  best  quality  of  retort  graphite  were 
used.  These  anodes,  to  be  sure,  become  saturated  with  gold 
bath,  and  for  that  reason  cannot  be  used  for  other  baths. 
When  not  required  for  some  time,  they  are  kept  in  a  vessel 
tilled  with  clean  water,  and  the  latter  is  added  to  the  bath  to 
replace  that  lost  by  evaporation. 

The  employment  as  anodes  of  platinum  strips  or  platinum 
-wire  may,  perhaps,  be  advocated  for  coloring  the  deposit,  i.  e., 
for  the  purpose  of  obtaining  certain  tones  of  color  when  gild- 
ing in  the  hot  bath.  By  allowing  the  platinum  anode  to  dip 
•only  slightly  in  the  bath  a  pale  gilding  is  obtained,  because 
the  current  thereby  becomes  weaker  ;  by  immersing  the  anode 
•deeper  the  color  becomes  more  yellow,  and  by  immersing  it 
entirely  the  tone  becomes  more  reddish. 


424  ELECTRO-DEPOSITION    OF    METALS. 

However,  instead  of  producing  these  effects  of  the  current- 
strength  by  the  anode,  which  requires  the  constant  presence  of 
the  operator,  it  is  better  to  obtain  the  coloration  by  means  of 
the  rheostat.  By  placing  the  switch  upon  "  strong,"  a  reddish- 
gold  tone  is  obtained,  and  by  placing  it  upon  "  weak,"  a  paler- 
gold  tone,  while  the  beautiful  gold-yellow  lies  in  the  middle- 
between  the  two  extremes.  However,  since  even  with  the  use 
of  gold  anodes  the  content  of  gold  in  the  bath  is  not  entirely 
restored,  the  bath  has  after  some  time  to  be  strengthened, 
which  is  effected  by  a  solution  of  fulminating  gold  or  chloride 
of  gold  in  potassium  cyanide,  according  to  the  composition  of 
the  bath. 

The  excess  of  potassiuni  cyanide  must  not  be  too  large, 
otherwise  the  gilding  will  be  pale  ;  but,  on  the  other  hand,  it 
must  not  be  too  small,  since  in  this  case  quite  a  strong  current 
would  have  to  be  used  to  effect  a  normal  deposition  of  gold, 
which,  besides,  would  not  be  dense  and  homogeneous.  Too- 
small  a  content  of  potassium  cyanide  is  indicated  by  the  gold 
anodes  showing  dark  streaks. 

As  in  the  silvering  baths,  the  excess  of  potassium  cyanide 
in  the  gold  baths  is  also  partially  converted  into  potassium 
carbonate  by  the  action  of  air,  heat,  etc.,  and  it  is,  therefore^ 
advisable  from  time  to  time  to  add  a  small  quantity  of  potas- 
sium cyanide. 

The  presence  of  larger  quantities  of  organic  substances- 
which  may  get  into  the  bath  by  dust  or  some  other  way, 
shows  itself,  as  a  rule,  by  a  brownish  coloration.  Such  baths- 
rarely  yield  a  beautiful  gold  color,  but  deposit  gold  of  a  dark 
tone. 

Unsightly  and  spotted  deposits  are  also  caused  by  a  con- 
tamination of  gold  baths  with  compounds  of  lime  which  reach 
the  bath  by  the  use  of  water  containing  much  lime,  or  by 
insufficient  removal  of  lime  paste  after  freeing  the  objects  from, 
grease. 

Tanks  for  gold  baths.  Gold  baths  for  cold  gilding  are  kept 
in  tanks  of  stoneware  or  enameled  iron,  or  small  baths  in* 


DEPOSITION    OF    GOLD. 


glass  tanks,  which,  to  protect  them  against  breaking,  are  placed 
in  a  wooden  box.  Baths  for  hot  gilding  require  enameled 
iron  tanks  in  which  they  can  be  heated  by  a  direct  fire,  or 
better,  by  placing  in  hot  water  (water  bath),  or  by  steam.  For 
small  gold  baths  for  hot  gilding,  a  porcelain  dish  resting 
upon  a  short-legged  iron  tripod  may  be  used  (Fig.  129).  Be- 
neath the  iron  tripod  is  a  gas  burner  supplied  with  gas  by 
means  of  a  flexible  India-rubber  tube  connected  to  an  ordinary 
gas  burner.  Across  the  porcelain  dish  are  placed  two  glass 
rods,  around  which  the  pole-wires  are  wrapped. 

In  heating  larger  baths  in  enameled  tanks  over  a  direct. 

FIG.  129.    * 


fire  it  may  happen  that  on  the  places  most  exposed  to  the 
heat  the  enamel  may  blister  and  peel  off;  it  is,  however, 
better  to  heat  the  baths  in  a  water  or  steam  bath.  For  this 
purpose  have  made  a  box  of  stout  iron  or  zinc  sheet  about 
}  inch  wider  and  longer,  and  about  4  inches  deeper  than  the 
enameled  tank  containing  the  gold  bath.  To  keep  the  level 
of  the  water  constant,  the  box  is  to  be  provided  with  a  water 
inlet-  and  overflow-pipe.  In  this  box  place  the  tank  so  that 
its  edges  rest  upon  those  of  the  box,  and  make  the  joints  tight 
with  tow.  The  water-bath  is  then  heated  over  a  gas  flame  or 


426  ELECTRO-DEPOSITION    OF    METALS. 

upon  a  hearth,  the  water  lost  by  evaporation  being  constantly 
replaced,  so  that  the  enameled  tank  is  always  to  half  its 
height  surrounded  by  hot  water.  For  heating  by  steam  the 
arrangement  is  the  same,  only  a  valve  for  the  introduction, 
and  a  pipe  for  the  discharge,  of  steam,  are  substituted  for  the 
water  inlet-  and  overflow-pipe. 

Execution  of  gold-plating. — Most  suitable  current-density, 
0.15  to  0.2  ampere.  Like  all  other  electro-plating  operations, 
it  is  advisable  to  effect  gold-plating  with  an  external  source  of 
current,  that  is,  to  use  a  battery  or  other  source  of  current 
separated  from  the  bath,  and  to  couple  the  apparatuses  as  pre- 
viously described  and  illustrated  by  Figs.  44  and  45. 

To  be  sure,  there  are  still  gilders  who  gild  without  a  battery 
or  separate  external  source  of  current  and  obtain  good  results, 
the  process  being,  as  a  rule,  employed  only  in  gilding  small 
articles.  The  apparatus  used  for  this  purpose  consists  of  a 
glass  vessel  containing  the  gold  solution  compounded  with  a 
large  excess  of  potassium  cyanide,  and  a  porous  clay  cup  filled 
with  very  dilute  sulphuric  acid  or  common  salt  solution,  which 
is  placed  in  the  glass  vessel.  Care  should  be  taken  to  have 
the  fluids  in  both  vessels  at  the  same  level.  Immerse  in  the 
clay  cup  an  amalgamated  zinc  cylinder  or  zinc  plate,  to  which 
a  copper  wire  is  soldered.  Outside  the  cup  this  copper  wire  is 
bent  downwards,  and  the  article  to  be  gilded,  which  dips  in 
the  gold  solution,  is  fastened  to  it.  In  working  with  this  ap- 
paratus there  is  always  a  loss  of  gold,  since  the  gold  solution 
penetrates  through  the  porous  cup,  and  on  coming  in  contact 
with  the  zinc  is  reduced  by  it,  the  gold  being  separated  as 
black  powder  upon  the  zinc.  In  cleaning  the  apparatus  this 
black  slime  has  to  be  carefully  collected  and  worked  for  fine 
gold. 

For  the  sake  of  greater  solidity,  only  articles  of  silver  and 
copper  and  its  alloys  should  be  directly  gilded,  while  all  other 
metals  are  best  first  brassed  or  coppered.  Cleaning  from  grease 
and  pickling  is  done  in  the  same  manner,  as  described  on  page 
:228.  The  preparation  of  the  articles  for  gilding  differs  from 


DEPOSITION    OF    GOLD.  427 

that  for  silvering  only  in  that  the  surfaces,  which  later  on  are 
•to  appear  with  high  luster,  are  not  artificially  roughened  with 
•emery,  pumice,  or  by  pickling,  because,  on  the  one  hand,  the 
.gold  deposit  seldom  needs  to  be  made  extravagantly  heavy, 
•and  the  rough  surface  formed  would  require  more  laborious 
polishing  with  the  burnishers ;  and,  on  the  other,  the  gold  de- 
posits adhere  quite  well  to  highly-polished  surfaces,  provided 
•the  current-strength  is  correctly  regulated,  and  the  bath 
accurately  composed  according  to  one  of  the  formula?  given. 
*Quicking  the  articles  before  gilding,  which  is  recommended 
by  some  authors,  is  not  necessary. 

The  current-strength  must,  under  no  circumstances,  be  so 
great  that  a  decomposition  of  water,  and  consequent  evolution 
•of  hydrogen  on  the  objects,  takes  place,  since  otherwise  the 
gold  would  not  deposit  in  a  reguline  and  coherent  form,  but  as 
•a,  brown  powder.  By  regulating  the  current-strength  so  that 
it  just  suffices  for  the  decomposition  of  the  bath,  and  avoiding 
&  considerable  surplus,  a  very  dense  and  uniform  deposit  is 
formed  ;  and  by  allowing  the  object  to  remain  long  enough  in 
the  bath,  a  beautiful,  mat  gold  deposit  can  be  obtained  in  all 
the  baths  prepared  according  to  the  formulae  given.  It  may, 
however,  be  mentioned  that  this  mode  of  mat  gilding  is  the 
most  expensive,  since  it  requires  a  very  heavy  deposit,  and  it 
will,  therefore,  be  better  to  matten  the  surface  previous  to 
gilding,  according  to  a  process  to  be  described  later  on. 

Constant  agitation  of  the  objects  in  the  baths,  or  of  the  lat- 
ter itself,  is  of  great  advantage  for  obtaining  good  gilding.  It 
is  evident  that  by  reason  of  the  small  amount  of  metal  in  the 
gold  baths,  especially  in  warm  ones,  the  strata  of  fluid  on  the 
•cathodes  become  rapidly  poor  in  metal,  and  if  care  be  not 
taken  to  replace  them  by  strata  of  fluid  richer  in  gold,  dis- 
turbances in  deposition  will  result. 

For  gilding  with  cold  baths,  two  freshly-filled  Bunsen  cells 
coupled  for  electro-motive  force  suffice  in  almost  all  cases, 
while  for  hot  baths  one  cell  is,  as  a  rule,  sufficient,  if  the 
anode  surface  is  not  too  small.  The  more  electro-positive  the 
metal  to  be  gilded  is,  the  weaker  the  current  can  and  must  be. 


428  ELECTRO-DEPOSITION    OF    METALS. 

Though  gold  solutions  are  good  conductors,  and,  therefore,, 
the  portions  of  the  articles  which  do  not  hang  directly  oppo- 
site the  anodes  gild  well,  for  solid  plating  of  larger  objects  it 
is  recommended  to  frequently  change  their  positions,  except 
when  they  are  entirely  surrounded  by  anodes. 

The  inner  surfaces  of  hollow-ware,  such  as  drinking-cups, 
milk  pitchers,  etc.,  are  best  plated  after  freeing  them  from 
grease  and  pickling,  by  filling  the  vessel  with  the  gold  bath 
and  suspending  a  current-carrying  gold  anode  in  the  center 
of  the  vessel,  while  the  outer  surface  of  the  latter  is  brought 
in  contact  with  the  negative  conducting  wire.  The  lips  of 
vessels  are  plated  by  placing  upon  them  a  cloth  rag  saturated 
with  the  gold  bath  and  covering  the  rag  with  the  gold  anode. 

For  gold-plating  in  the  cold  bath  the  process  is  as  follows : 
The  objects,  thoroughly  freed  from  grease  and  pickled  (and  if 
of  iron,  zinc,  tin,  Britannia,  etc.,  previously  coppered),  are 
suspended  in  the  bath  by  copper  wires,  where  they  remain 
with  a  weak  current  until  in  about  8  or  10  minutes  they  ap- 
pear uniformly  plated.  At  this  stage  they  are  taken  from  the 
bath,  rinsed  in  a  pot  filled  with  water,  and  the  latter,  after 
having  been  used  for  some  time,  is  added  to  the  bath  to  re- 
place the  water  lost  by  evaporation.  The  articles  are  finally 
brushed  with  a  fine  brass  scratch-brush  and  tartar  solution,, 
thoroughly  rinsed,  again  freed  from  grease  by  brushing  with 
lime-paste  and  then  returned  to  the  bath,  where  they  remain 
until  they  have  acquired  a  deposit  of  sufficient  thickness. 

When  an  article  is  to  have  a  very  heavy  deposit,  it  is  ad- 
visable to  scratch-brush  it  several  times  with  the  use  of  tartar 
or  its  solution,  or  with  a  solution  of  size  and  water,  between 
the  intermediate  coats  of  gold.  By  these  means  a  very  durable 
and  lasting  coating  of  gold  will  be  secured.  For  gold  plating 
by  weight  the  same  plan  as  given  for  silver-plating  by  weight 
(p.  382)  is  pursued. 

For  gold-plating  with  the  hot  bath,  the  operations  are  the 
same,  with  the  exception  that  a  weaker  current  is  introduced 
into  the  bath  and  the  time  of  the  plating  process  shortened. 


DEPOSITION    OF    GOLD.  429 

Frequent  scratch-brushing  also  increases  the  solidity  of  the 
-deposit  and  prevents  its  prematurely  turning  to  a  dead  brown- 
black.  Since  in  hot  plating  more  gold  than  intended  is 
readily  deposited,  it  is  especially  advisable  to  place  a  rheostat 
and  voltmeter  in  the  circuit,  as  otherwise  the  operator  must 
remain  standing  along-side  of  the  bath  and  regulate  the  effect 
of  the  current  by  immersing  the  anodes  more  or  less. 

When  taken  from  the  bath,  the  finished  gilded  objects  should 
show  a  deep  yellow  tone,  which,  after  polishing,  yields  a  full 
gold  color.  If  the  objects  come  from  the  bath  with  a  pale 
gold  tone,  the  deposit,  after  polishing,  shows  a  meager,  pale 
gold  color,  which  is  without  effect.  Gold  deposits  of  a  dark 
or  brown  color  also  do  not  yield  a  sad  gold  tone. 

With  a  somewhat  considerable  excess  of  potassium  cyanide, 
and  if  the  objects  to  be  plated  are  not  rapidly  brought  in  con- 
tact with  the  current-carrying  object  rod,  hot  gold  baths  cause 
the  solution  of  some  metal.  Therefore  when  silver  or  silver- 
plated  objects  are  constantly  plated  in  them  they  yield  a  some- 
what greenish  gilding  in  consequence  of  the  absorption  of 
silver,  or  a  reddish  gilding  due  to  the  absorption  of  copper,  if 
copper  or  coppered  articles  are  constantly  plated  in  them. 
Hence,  for  the  production  of  such  green  or  reddish  color, 
gold-plating  baths  which  have  thus  become  argentiferous  or 
cupriferous,  may  be  advantageously  used.  In  order  to  obtain 
a  deposit  of  green  or  red  gold  with  fresh  baths,  the  tone-giving 
addition  of  metal  must  be  artificially  effected,  as  will  pres- 
ently be  seen. 

If,  however,  such  extreme  tones  are  not  desired,  the  content 
of  gold  in  the  baths  may  be  exhausted  for  preliminary  plat- 
ing with  the  use  of  platinum  anodes,  the  sad  gold  color  being 
then  given  in  a  freshly  prepared  bath. 

The  gold  deposits  are  polished  in  the  same  manner  as  silver 
deposits,  with  the  burnisher  and  red  ochre,  and  moistening 
with  solution  of  soap,  decoction  of  flaxseed,  or  soap-root,  etc. 
For  less  heavy  gilding  the  articles,  previous  to  gilding,  are 
given  high  luster,  and  after  gilding,  burnished  with  rouge 
and  buckskin. 


430  ELECTRO-DEPOSITION    OF    METALS. 

Red-gilding.  In  order  to  obtain  a  red  gold  with  the  formulae- 
given,  a  certain  addition  of  copper  cyanide  dissolved  in  potas- 
sium cyanide  has  to  be  made  to  them.  The  quantity  of  such 
addition  cannot  be  well  expressed  by  figures,  since  the  current 
strength  with  which  the  articles  are  plated  exerts  considerable 
influence.  It  is  best  to  triturate  the  copper  cyanide  in  a  mor- 
tar to  a  paste  with  water,  and  add  of  this  paste  to  a  moderately 
concentrated  potassium  cyanide  solution  as  long  as  copper 
cyanide  is  dissolved.  Of  this  copper  solution  add,  gradually 
and  in  not  too  large  portions,  to  the  gold  solution  until,  with 
the  current-strength  used,  the  gold  deposit  shows  the  desired 
red  tone,  and  if  fine  gold  anodes  are  used,  the  bath  is  kept 
constant  with  this  content  of  copper  by  an  occasional  addition 
of  the  above-mentioned  copper  solution. 

The  absorption  of  copper  in  the  bath  may  also  be  effected 
by  suspending,  in  place  of  gold  anodes,  anodes  of  copper  or 
copper-gold  alloys,  for  instance,  fourteen-carat  gold,  and  allow- 
ing the  current  to  circulate  (suspension  of  a  few  gold  anodes 
to  the  object-rod).  The  direct  addition  of  copper  cyanider 
however,  deserves  the  preference. 

In  place  of  preparing  the  solution  of  copper  cyanide  in 
potassium  cyanide,  commercial  crystallized  potassium-copper 
cyanide  may  be  used.  It  is  dissolved  in  warm  water,  and  of 
the  solution  a  sufficient  quantity  is  gradually  added  to  the 
gold  bath. 

For  the  determination  of  the  content  of  copper  required  for 
the  purpose  of  obtaining  a  beautiful  red  gold,  a  bath  for  hot 
gilding  which  contained  10.8  grains  of  gold  per  quart  wa& 
compounded  with  a  solution  of  copper  cyanide  in  potassium 
cyanide  with  1.08  grains  content  of  copper.  The  tone  of  the 
gilding,  which  previously  was  pure  yellow,  immediately  passed 
into  a  pale  red  gold.  By  the  further  addition  of  1.08  grains 
of  copper,  a  fiery  red  gold  tone  was  obtained,  while  a  third 
addition  of  1.08  grains  of  copper  yielded  a  color  more  ap- 
proaching that  of  copper  than  of  gold.  These  experiments 
show  that  20  per  cent,  of  copper  of  the  weight  of  gold  con- 


DEPOSITION    OF    GOLD.  431' 

tained  in  the  bath  seems  to  be  the  most  suitable  proportion 
for  obtaining  a  beautiful  red  gold. 

Rings,  watch-chains  and  other  objects  of  base  metal  are  fre- 
quently to  be  plated  with  red  gold,  so  as  to  show  no  percepti- 
ble sign  of  having  been  attacked  by  nitric  acid,  even  after  re- 
maining in  it  for  several  hours.  This  may  be  effected  by  first 
giving  the  objects  a  deposit  of  a  strongly  yellow  color  by  gild- 
ing in  a  bath  containing  10.8  to  15.43  grains  of  gold  per  quart 
and  then  coloring  them  in  the  red  gilding  bath.  This  process 
may  be  called  an  imitation  of  mechanical  gold  plating,  and  is 
frequently  made  use  of  in  the  jewelry  industry. 

A  method  of  gilding  chains'  and  other  articles  manufac- 
tured from  common  metal,  in  imitation  of  genuine  gold 
articles  is  given  by  Gee  as  follows :  A  bath  is  prepared  by 
dissolving  a  quantity  of  pure  gold  and  making  a  solution  of 
it  in  the  usual  manner,  and  then  using  a  large  copper  anode 
instead  of  a  gold  one  in  the  process  of  gilding. 

The  articles  are  gilt  until  they  stand  the  acid  test,  when 
they  are  well  burnished  until  they  present  a  bright  gold-like 
appearance.  If  the  articles  are  slightly  gilt  as  a  first  process 
arid  then  burnished,  and  afterwards  more  thickly  gilt  and 
again  burnished,  much  less  gold  is  required  than  if  the  pro- 
cess is  conducted  straight  to  the  end  without  any  inter- 
mediate burnishing.  The  burnishing  stops  up  all  the  pores 
of  the  metal  by  the  adoption  of  this  plan,  and  more  quickly 
renders  the  articles  gilt  acid  proof  and  that  at  the  expense  of 
much  less  gold.  When  the  solution  begins  to  gild  of  an  in- 
ferior color  it  is  abandoned  and  another  one  made.  It  pro- 
duces a  surface  alloy  of  about  16  or  18  carat,  and  well  answers 
the  purpose  for  which  it  has  been  designed. 

Green  gilding.  To  obtain  greenish  gilding,  solution  of 
cyanide  or  chloride  of  silver  in  potassium  cyanide  has  to  be 
added  to  the  gold  bath.  It  is  not  easy  to  prepare  greenish 
gilding  of  a  pleasing  color,  and  to  obtain  it  the  current-strength 
must  be  accurately  proportioned  to  the  object-surface,  since 
with  too  weak  a  current  silver  predominates  in  the  deposit,. 


432  ELECTRO-DEPOSITION    OF    METALS. 

the  gilding  then  turning  out  whitish,  while  too  strong  a  cur- 
rent deposits  too  much  gold  in  proportion  to  silver,  the  gilding 
becoming  yellow,  but  not  green. 

Rose-color  gilding  may  be  obtained  by  the  addition  of  suit- 
able quantities  of  copper  and  silver  solutions,  but  such  colora- 
tion requires  much  attention  and  thought. 

Rose  gold  solution. — Probably  one  of  the  best  solutions  for 
the  rose  gold,  sometimes  also  termed  old  gold  is,  according  to 
Mr.  Chas.  H.  Proctor,*  made  from  J  oz.  of  pure  24-karat  gold, 
dissolved  in  aqua  regia  in  the  usual  manner,  then  precipitated 
as  fulminate  with  ammonia  (26°),  and  then  well  washed. 
Add  the  gold  salt  to  a  solution  of  1  gallon  of  cyanide  solution, 
standing  2  to  3°  Be,  and  add  J  oz.  of  hyposulphite  of  sodium 
to  each  gallon  of  solution  so  prepared.  This  solution  will 
produce  a  good  flash  gold  with  a  weak  current.  Cheap  rose 
gold  work  is  first  acid  copper  plated  for  a  few  minutes,  then 
relieved  on  the  high  lights,  and  then  gilded.  Gold  work  is 
run  for  five  to  ten  minutes  with  a  strong  current,  according  to 
the  tone  required,  then  relieved  with  sodium  bicarbonate  in- 
stead of  pumice  stone.  ' 

To  produce  a  rose  gold  finish  without  the  use  of  gold  a 
number  of  concerns  are  using  the  Electrochroma  Process,  in 
which  the  articles  are  immersed  in  a  special  bath  in  the  same 
manner  as  employed  in  plating.  In  a  minute  or  two  the 
articles  are  coated  with  a  pinkish  yellow  surface  that  resembles 
rose  gold.  The  surface  is  afterwards  relieved  to  produce  a 
•contrast  effect  on  the  high  lights. 

This  finish  can  also  be  imitated  very  successfully  by  the 
following  method  :  All  articles,  except  those  of  brass,  should 
be  previously  brass-plated  and  then  a  surface  similar  to  the 
brush  brass  finish  produced.  Use  floated  silax  instead  of 
pumice  stone  so  that  the  surface  will  be  even  and  not  have  a 
scratchy  appearance.  Then  gold  lacquer,  using  a  yellowish 
instead  of  a  red  toned  lacquer.  The  surface  should  be  thor- 

*  Metal  Industry,  June,  1913. 


DEPOSITION    OF    GOLD.  433 

•oughly  dried  on  the  lacquer  heater.  The  rose  tone  is  then 
produced  by  mixing  dry  orange  chrome  and  a  very  little 
finely  powdered  gold  rouge,  mixed  with  turpentine  and  a  tea- 
spoonful  of  turpentine  varnish  per  pint  of  the  mixture.  This 
should  be  mixed  to  a  thinly  fluid  paint  and  then  applied  to 
the  detail  work  with  a  soft  brush.  The  articles  should  then 
be  dried  for  a  short  time  by  the  aid  of  heat  and  allowed  to 
become  cool.  The  surface  should  be  opaque  without  any 
luster  when  dry.  Now  mix  up  equal  parts  of  boiled  linseed 
•oil  and  turpentine  and  use  this  for  reducing  the  color  from  the 
surface.  To  accomplish  this  operation,  moisten  soft  rags  with 
the  mixture  and  remove  the  colors  from  the  high  lights  or 
detail  work.  After  this  is  done  the  articles  will  have  the  ap- 
pearance of  true  rose  gold. 

For  the  sake  of  completeness,  a  method  of  gilding  which  is 
a  combination  of  fire-gilding  with  electro-deposition,  may 
here  be  mentioned,  though  experiments  made  with  it  failed  to 
show  the  advantages  claimed  for  it,  because  it  does  not  yield 
as  dense  a  deposit  as  fire-gilding,  nor  can  the  volatilization  of 
mercury  be  avoided,  the  latter  operation  being  the  most  dan- 
gerous part  of  fire-gilding. 

According  to  Du  Fresne,  the  process  is  as  follows : 

The  articles  are  first  coated  with  mercury,  with  the  assist- 
ance of  the  current,  in  a  mercurial  solution  consisting  of 
cyanide  of  mercury  in  potassium  cyanide,  with  additions  of 
carbonate  and  phosphate  of  soda,  then  gilded  in  an  ordinary 
gilding-bath,  next  again  coated  with  mercury,  then  again 
gilded,  and  so  on,  until  a  deposit  of  sufficient  thickness  is 
obtained.  The  mercury  is  then  evaporated  over  glowing 
coals,  and  the  articles,  after  scratch-brushing,  are  burnished. 

According  to  another  process,  the  articles  are  gilded  in  a  bath, 
consisting  of  98  per  cent,  potassium  cyanide  1.2  qzs.,  cyanide 
of  gold  92J  grains,  cyanide  of  mercury  22J  grains,  distilled 
water  1  quart,  a  strong  current  being  used.  When  the  objects 
are  sufficiently  gilded,  the  mercury  is  evaporated  in  the  above- 
mentioned  manner,  and  the  objects  are  scratch-brushed,  and 
finally  polished. 
28 


434  ELECTRO-DEPOSITION    OF    METALS. 

Mat  gilding. — As  previously  mentioned,  a  beautiful  mat 
gold  deposit  may  be  obtained  by  the  use  of  any  of  the  for- 
mulas given,  and  a  current  correctly  regulated,  and  allowing 
sufficient  time  for  gilding.  The  heavy  deposit  of  gold  required 
for  this  process  makes  it,  however,  too  expensive,  and  it  is, 
therefore,  advisable  to  produce  mat  gilding  by  previously 
matting  the  basis-surface,  since  then  a  thinner  deposit  of  gold 
will  answer  very  well.  The  process  of  graining  will  be 
referred  to  later  on  under  "  Silvering  by  Contact,"  etc. 

Another  method  is  to  mat  the  first  slight  deposit  by  means 
of  brass  or  steel-wire  brushes,  and  then  to  give  a  second  de- 
posit of  gold,  which  also  turns  out  mat  upon  the  matted 
surface.  The  character  of  the  mat  produced  depends  on  the 
thickness  of  the  wire  of  the  brushes.  Thicker  wire  gives  a 
mat  of  a  coarser  grain,  and  thinner  wire  one  of  a  finer  grain. 

Objects  may  be  readily  matted  with  the  use  of  the  sand 
blast,  after  which  they  are  quickly  drawn  through  the  bright 
dipping  bath,  thoroughly  rinsed,  and  brought  into  the  gold 
bath. 

Matting  by  chemical  or  electro-chemical  means  is  effected  by 
one  of  the  following  methods  : 

For  this  purpose  the  mixture  of  1  volume  of  saturated  solu- 
tion of  bichromate  of  potash  and  2  volumes  of  concentrated 
hydrochloric  acid,  mentioned  on  p.  225,  may  be  used.  Brass 
articles  are  allowed  to  remain  several  hours  in  the  mixture^ 
and  are  then  quickly  drawn  through  the  bright-dipping  bath. 
Copper  alloys  might  also  be  successfully  matted  by  suspend- 
ing them  as  anodes  in  a  mixture  of  90  parts  water  and  10 
parts  sulphuric  acid,  and  drawing  the  matted  articles  through 
the  bright-dipping  bath. 

Or,  they  are  mat-silvered,  and  the  gold  is  deposited  upon 
the  matted  .layer  of  silver.  Articles  gilded  upon  a  mat  silver 
basis,  however,  acquire  before  long  an  ugly  appearance,  since- 
in  an  atmosphere  containing  sulphuretted  hydrogen  the  silver 
turns  black,  even  under  the  layer  of  gold  and  shines  through. 

More  advantageous  is  the  process  of  providing  the  articles 


DEPOSITION    OF    GOLD.  435 

with  a  mat  copper  coating  in  the  acid  galvanoplastic  bath. 
They  are  then  drawn  through  a  not  too  strong  pickle,  rinsed, 
and  gilded.  This  process  is  used  for  the  so-called  French 
clock  gilding,  and  yields  a  very  sad,  beautiful  gilding.  The 
articles  consisting  of  zinc  are  first  heavily  coppered  in  a  cyanide 
copper  bath,  then  matted  in  the  acid  copper  bath  (see  "  Gal- 
vanoplasty "),  care  being  taken  that  the  slinging  wire  is  in 
contact  with  the  object-rod,  which  conducts  the  current,  be- 
fore the  coppered  zinc  objects  is  suspended  in  the  bath.  This 
process  of  coppering  zinc  in  the  acid  copper  bath  is,  however, 
quite  a  delicate  operation,  and  it  will  frequently  be  noticed, 
even  with  apparently  very  heavy  coppering  in  the  cyanide 
copper  bath,  that  in  suspending  the  articles  in  the  acid  bath, 
brownish-black  places  appear  on  which,  by  contact  of  the 
acid  bath  with  zinc,  copper  in  a  pulverulent  form  is  depos- 
ited. When  this  is  observed,  the  articles  must  be  immedi- 
ately taken  from  the  bath,  thoroughly  scratch-brushed,  and 
again  thoroughly  and  heavily  coppered  in  the  cyanide  copper 
bath,  before  replacing  them  in  the  acid  copper  bath.  It  may 
be  recommended  to  provide  the  coppered  zinc  articles  with  a 
thick  deposit  of  nickel,  and  then  to  copper  them  mat  in  the 
acid  bath,  the  percentage  of  unsuccessful  coppering  being 
much  smaller  than  without  previous  nickeling.  The  mat- 
coppered  articles  are  rapidly  drawn  through  the  bright-dipping 
bath  and  then  gilded,  the  bath  prepared,  according  to  formula 
III,  and  heated  to  about  140°  F.,  being  very  suitable  for  the 
purpose. 

Coloring  of  the  gilding.  It  has  been  repeatedly  mentioned 
that  the  most  rational  and  simple  process  of  giving  certain 
tones  of  color  to  the  gilding  is  by  means  of  a  stronger  or 
weaker  current.  Many  operators,  however,  cling  to  the  old 
method  of  effecting  the  coloration  by  gilder's  wax  or  brushing 
with  certain  mixtures,  and  for  this  reason  this  process,  which 
is  generally  used  for  coloring  fire-gilding,  shall  be  briefly 
mentioned. 

To  impart  to  the  gold-deposit  a  redder  color,  the  gilding-wax 


436  ELECTRO-DEPOSITION    OF    METALS. 

is  prepared  with  a  greater  content  of  copper,  while  for  greenish 
gilding  more  zinc-salt  is  added.  There  are  innumerable  re- 
ceipts for  the  preparation  of  gilding  wax,  nearly  every  gilder 
having  his  own  receipt,  which  he  considers  superior  to  all 
others.  Only  two  formulae  which  yield  good  results  will  have 
to  be  given  one  (I)  for  reddish  gilding  and  one  (II)  for  greenish 
gilding. 

I.  Wax  12  parts  by  weight,  pulverized  verdigris  8,  pulver- 
ized sulphate  of  zinc  4,  copper  scales  4,  borax  1,  pulverized 
bloodstone  6,  copperas  2. 

II.  Wax  12  parts  by  weight,  pulverized  verdigris  4,  pulver- 
ized sulphate  of  zinc  8,  copper  scales  2,  borax  4,  pulverized 
bloodstone  6,  copperas  2. 

Gilder's  wax  is  prepared  as  follows :  Melt  the  wax  in  an 
iron  kettle,  add  to  the  melted  mass,  while  constantly  stirring, 
the  other  ingredients,  pulverized  and  intimately  mixed,  in 
small  portions,  and  stir  until  cold,  so  that  the  powder  cannot 
settle  on  the  bottom  or  form  lumps.  "Finally,  mould  the  soft 
mass  into  sticks  about  J  inch  in  diameter. 

Gilder's  \\ax  is  applied  as  follows:  Coat  the  heated  gilded 
articles  uniformly  with  the  wax,  and  burn  off  over  a  charcoal 
fire,  frequently  turning  the  articles.  After  the  wax  flame  is 
extinguished,  plunge  the  articles  into  water,  scratch-brush 
with  wine-vinegar,  dry  in  sawdust,  and  polish. 

To  give  gilded  articles  a  beautiful,  rich  appearance,  the  fol- 
lowing process  may  also  be  used  :  Mix  3  parts  by  weight  of 
pulverized  alum,  6  of  saltpetre,  3  of  sulphate  of  zinc,  and  3  of 
common  salt,  with  sufficient  water  to  form  a  thinly-fluid 
paste.  Apply  this  paste  as  uniformly  as  possible  to  the  articles 
by  means  of  a  brush,  and  after  drying,  heat  the  coating  upon 
an  iron  plate  until  it  turns  black ;  then  wash  in  water, 
scratch-brush  with  wine-vinegar,  dry  and  polish. 

According  to  a  French  receipt,  the  same  result  is  attained  by 
mixing  pulverized  blue  vitriol  3  parts  by  weight,  verdigris  7, 
ammonium  chloride  6,  and  saltpetre  6,  with  acetic  acid  31  ; 
immersing  the  gilded  articles  in  the  mixture,  or  applying  the 


DEPOSITION    OF    GOLD.  437 

latter  with  a  brush  ;  then  heating  the  objects  upon  a  hot  iron 
plate  until  they  turn  black,  and,  after  cooling,  pickling  in 
concentrated  sulphuric  acid. 

Some  gilders  improve  bad  tones  of  gilding  by  immersing  the 
articles  in  dilute  solution  of  nitrate  of  mercury  until  the  gild- 
ing appears  white.  The  mercury  is  then  evaporated  over  a 
flame  and  the  articles  are  scratch-brushed.  Others  apply  a 
paste  of  pulverized  borax  and  water,  heat  until  the  borax 
melts,  and  then  quickly  immerse  in  dilute  sulphuric  acid. 

Incrustations  with  gold  are  produced  in  the  same  manner  as 
incrustations  with  silver,  described  on  p.  403. 

Gilding  *o/  metallic  wire  and  gauze. — Fine  wire  of  gilded 
copper  and  brass  is  much  used  in  the  manufacture  of  metallic 
fringes  and  lace,  for  epaulettes  and  other  purposes.  The  fine 
copper  and  brass  wires  being  drawn  through  the  draw-irons 
and  wound  upon  spools  by  special  machines,  and  hence  not 
touched  by  the  hands,  freeing  from  grease  may,  as  a  rule,  be 
omitted.  The  first  requisite  for  gilding  is  a  good  winding 
machine,  which  draws  the  wires  through  the  gold  bath  and 
wash-boxes,  and  further  effects  the  winding  of  the  wire  upon 
spools.  The  principal  demand  made  in  the  construction  of 
such  a  machine  is  that  by  means  of  a  simple  manipulation  a 
great  variation  in  the  speed  with  which  the  wire  or  gauze 
passes  through  the  gold  bath  can  be  obtained.  This  is  neces- 
sary in  order  to  be  able  to  regulate  the  thickness  of  the  gilding 
by  the  quicker  or  slower  passage  of  the  wire.  A  machine  well 
adapted  for  this  purpose  is  that  constructed  by  J.  W.  Spaeth, 
and  shown  in  Fig.  130. 

The  variation  in  the  passage  of  the  wire  is  attained  by  the 
two  friction-pulleys  F,  which  sit  upon  a  common  shaft  with 
the  driving  pulley  R,  and  transmit  their  velocity  by  means  of 
the  friction-pistons  KKf  to  the  friction-pulley  Ff,  which  is 
firmly  connected  to  the  belt-pulley  R  driving  the  spool  spindle. 
Since  by  a  simple  device  the  pistons  K  and  K'  may  be  shifted, 
it  is  clear  that  the  transmission  of  the  number  of  revolutions 
from  F  to  F'  is  dependent  on  the  position  of  the  friction- 


438 


ELECTRO-DEPOSITION    OF    METALS. 


pistons  K  and  K',  and  that  the  velocity  will  be  the  greater 
the  shorter  the  distance  they  are  from  the  center  of  friction- 
pulleys  jPand  P.  In  order  that  the  friction  between  F,  K 
and  F'  may  always  be  sufficient  for  the  transmission  of  the 
motion,  even  when  the  pistons  are  worn,  four  weights,  G,  are 
provided,  which  press  the  above-mentioned  parts  firmly  against 
each  other. 

In  front  of  each,  spool  of  this  machine  is  inserted  a  small 

FIG.  130. 


enameled  iron  tank  which  contains  the  gold  bath,  and  is 
heated  by  a  gas  flame  to  about  167°  F.  Between  this  bath 
and  the  winding  machine  is  another  small  tank  with  hot 
water  in  which  the  gilded  wire  is  rinsed. 

The  wire  unwinds  from  a  reel  placed  in  front  of  the  gold 
baths,  runs  over  a  brass  drum  which  is  connected  to  the  nega- 
tive pole  of  the  source  of  current  and  transmits  the  current  to 
the  wire.  The  dipping  of  the  wire  into  the  gold  bath  is 
effected  by  porcelain  drums,  which  are  secured  to  heavy 
pieces  of  lead  placed  across  the  tanks,  as  shown  in  Fig.  131. 
The  gilded  wire  being  wound  upon  the  spools  of  the  winding 


DEPOSITION    OF    GOLD.  439 

machine,  these  spools  are  removed  and  thoroughly  dried  in 
the  drying  chamber.  The  wire  is  then  again  reeled  off  onto 
a  simple  reel,  in  doing  which  it  is  best  to  pass  it  through  be- 
tween two  soft  pieces  of  leather  to  increase  its  luster. 

For  gilding  wire  the  most  suitable  gold  bath  is  that  pre- 
pared according  to  formula  IV.  The  electro-motive  force 
should  be  from  6  to  8  volts,  in  order  to  produce  a  deposit  of 
sufficient  thickness,  even  when  the  wire  passes  at  the  most 
rapid  rate  through  the  bath.  For  this  reason  a  dynamo  with 
•a  voltage  of  10  volts  is  almost  exclusively  used  for  wire  gild- 
ing. 

As  a  rule  an  anode  of  platinum — a  strip  of  platinum  sheet 
— of  the  same  length  as  the  tank  is  placed  upon  the  bottom 
of  the  latter,  and  connected  by  means  of  platinum  wire  to  the 
positive  pole  of  the  source  of  current.  The  use  of  gold  anodes 

FIG.  131. 


for  wire  gilding  is  not  required,  since  the  small  gold  baths — 
generally  only  2  to  4  quarts — are  as  far  as  possible  to  be 
worked  till  exhausted,  when  they  are  replaced  by  fresh  baths. 

In  place  of  platinum  anodes,  Stockmeir  recommends  the 
use  of  blued  Bessemer  steel  anodes  for  wire  gilding.  In  this 
•case  there  can  be  no  objection  to  steel  anodes,  because  the 
baths  are  rapidly  exhausted,  and  then  go  amongst  the  gold- 
residues.  But,  nevertheless,  the  use  of  an  indestructible  plati- 
num anode  would  appear  to  deserve  the  preference,  the  baths 
being  without  doubt  kept  cleaner  than  with  steel  anodes. 

Silver-plated  wires  are,  as  a  rule,  to  be  gilded,  and  since  the 
•color  of  the  basis-metal  exerts  an  influence  upon  the  gilding, 
Stockheimer  recommends  brassing  the  silver-plated  or  solid 
silver  wires  previous  to  gilding,  because  a  gold-deposit  of  less 


440  .     ELECTRO-DEPOSITION    OF    METALS. 

thickness  than  for  covering  the  white  silver,  would  thus  be- 
required.  The  proposition  to  gild  nickeled  wires,  in  place  of 
silver-plated  wires,  because  they  are  less  subject  to  rapid  dis- 
coloration in  an  atmosphere  containing  sulphuretted  hydro- 
gen, also  deserves  consideration. 

Stripping  gold  from  gilded  articles. — Gilded  articles  of'  iron 
and  steel  are  best  stripped  by  treating  them  as  anodes  in  a 
solution  of  from  2  and  2  j  ozs.  of  98  per  cent,  potassium  cyan- 
ide in  1  quart  of  water,  and  suspending  a  copper  plate  greased 
with  oil  or  tallow  as  the  cathode.  Gilded  silverware  is  readily 
stripped  by  heating  to  ignition,  and  then  immersing  in  dilute- 
sulphuric  acid,  whereby  the  layer  of  gold  cracks  off,  the  heat- 
ing and  subsequent  immersion  in  dilute  sulphuric  acid  being 
repeated  until  all  the  gold  is  removed.  Before  heating  and 
immersing  in  dilute  sulphuric  acid,  the  articles  may  ffifrst  be- 
provided  with  a  coating  of  a  paste  of  ammonia  chloride,, 
flowers  of  sulphur,  borax  and  nitrate  of  potash  which  is  allowed! 
to  dry.  On  the  bottom  of  the  vessel  containing  the  dilute 
sulphuric  acid,  the  gold  will  be  found  in  laminae  and  scales,, 
which  are  boiled  with  pure  sulphuric  acid,  washed  and  finally 
dissolved  in  aqua  regia,  and  made  into  chloride  of  gold  or 
fulminating  gold. 

To  strip  articles  of  silver,  copper  or  German  silver  which  will 
not  bear  heating,  the  solution  of  gold  may  be  effected  in  a 
mixture  of  1  Ib.  of  fuming  sulphuric  acid,  2.64  ozs.  of  con- 
centrated hydrochloric  acid,  and  1.3  ozs.  of  nitric  acid  of  40° 
Be.  Dip  the  articles  in  the  warm  acid  mixture,  and  observe 
the  progressive  action  of  the  mixture  by  frequently  removing 
the  articles  from  it.  The  articles  to  be  treated  must  be  per- 
fectly dry  before  immersing  in  the  acid  mixture,  and  care 
must  be  had  to  preserve  the  latter  from  dilution  with  water  in 
order  to  prevent  the  acids  from  acting  upon  the  basis-metal. 

The  process  by  which  scratched  or  rubbed  rings  are,  so  to 
say,  electrolytically  smoothed  and  polished,  may  be  called  a 
sort  of  stripping.  For  this  purpose  the  rings  are  suspended  a& 
anodes  in  a  bath  consisting  of :  Water  1  quart,  yellow  prussiate- 


DEPOSITION    OF    GOLD.  441 

of  potash  1  oz.,  99  per  cent,  potassium  cyanide  T7^  ozs.  By 
conducting  a  current  of  high  electro-motive  force,  of  about  20 
to  25  volts,  through  the  bath  any  roughness  or  unevenness  is 
in  a  few  minutes  removed,  and  the  rings  will  be  almost  per- 
fectly smooth  when  taken  from  the  bath.  A  sheet  of  gold  or 
platinum  is  used  as  cathode. 

Determination  of  genuine  gilding. — Objects  apparent  gilded 
are  rubbed  upon  the  touchstone,  and  the  streak  obtained  is 
treated  with  pure  nitric  acid  of  1.30  to  1.35  specific  gravity. 
The  metal  contained  in  the  streak  thereby  dissolves,  and  as  far 
as  it  is  not  gold,  disappears,  while  the  gold  remains  behind. 
The  stone  should  be  thoroughly  cleansed  before  each  operation? 
and  the  streak  should  be  made,  not  with  an  edge  or  a  corner 
of  the  object  to  be  tested,  but  with  a  broader  surface.  If  no 
gold  remains  upon  the  stone,  but  there  is  nevertheless,  a  sus- 
picion of  the  article  being  slightly  gilded,  proceed  with  small 
articles  as  follows:  Take  hold  of  the  article  with  a  pair  of 
tweezers,  and  after  washing  it  first  with  alcohol,  and  then  with 
ether,  and  drying  upon  blotting  paper,  pour  over  it  in  a  test 
glass,  cleansed  with  alcohol  or  ether,  according  to  the  weight 
of  the  article,  0.084  to  5.64  drachms  of  nitric  acid  of  1.30  spe- 
cific gravity  free  from  chlorine.  The  article  will  be  immedi- 
ately dissolved,  and  if  it  has  been  gilded  never  so  slightly,  per- 
ceptible gold  spangles  will  remain  upon  the  bottom  of  the 
glass. 

Examination  of  Gold  Baths. 

The  determination  of  free  potassium  cyanide  and  of  the 
potassium  carbonate  which  is  formed,  is  effected  in  the  same 
manner  as  given  under  "  Examination  of  copper  baths  and 
of  silver  baths." 

The  determination  of  the  gold  is  effected  by  the  electrolytic 
method.  With  baths  poor  in  gold,  50  cubic  centimeters  are 
used  for  electrolysis,  and  with  baths  rich  in  gold,  25  cubic 
centimeters.  After  diluting  with  water  to  within  1  centimeter 
of  the  rim  of  the  platinum  dish,  the  liquid  is  electrolyzed  for 


442  ELECTRO-DEPOSITION    OF    METALS. 

about  three  hours  with  a  current-density  ND  100  =  0.067 
amp&re,  the  complete  separation  of  the  gold  being  recognized 
by  a  platinum  strip  suspended  over  the  rim  of  the  dish  and 
dipping  into  the  fluid  showing  in  fifteen  minutes  no  trace  of 
a  separation  of  gold. 

The  dish  is  then  washed,  rinsed  with  alcohol,  and  dried  at 
212°  F.  To  obtain  the  content  of  gold  in  grammes  per  liter  of 
bath,  multiply  the  weight  of  the  precipitate  by  20,  when  50 
cubic  centimeters,  or  by  40,  when  25  cubic  centimeters,  of  the 
bath  have  been  used. 

The  content  of  gold  in  the  baths  declines  constantly,  es- 
pecially with  the  use  of  platinum  and  carbon  anodes.  For 
strengthening  the  bath  neutral  gold  chloride  dissolved  in 
potassium  cyanide  is  used,  2  grammes  neutral  gold  chloride 
and  1.4  grammes  99  per  cent,  potassium  cyanide  dissolved  in 
a  small  quantity  of  water  or  directly  in  the  bath,  being  re- 
quired for  every  gramme  of  gold  deficit  in  the  baths. 

The  determination  of  gold  described  above  is  suitable  only 
for  baths  prepared  with  potassium  cyanide,  which  contain  the 
gold  in  the  form  of  potassium-gold  cyanide.  The  determina- 
tion of  gold  in  baths  prepared  with  yellow  prussiate  of  potash 
is  more  difficult  and  should  be  made  by  a  skilled  analyst. 

Recovery  of  gold  from  gold  baths,  etc.  To  recover  the  gold 
from  old  cyanide  gilding  baths,  evaporate  the  baths  to  dry- 
ness,  mix  the  residue  with  litharge,  and  fuse  the  mixture. 
The  gold  is  contained  in  the  lead  button  thus  obtained.  The 
latter  is  then  dissolved  in  nitric  acid,  whereby  the  gold  re- 
mains behind  in  the  form  of  spangles.  These  spangles  are 
filtered  off  and  dissolved  in  aqua  regia. 

The  recovery  of  gold  from  gold  baths  may  also  be  advan- 
tageously effected  by  precipitation  with  zinc  dust  according 
to  the  same  process  as  given  for  the  recovery  of  silver,  p.  413. 
After  removing  the  zinc  by  means  of  hydrochloric  acid  and 
washing  the  gold  powder,  the  latter  is  dissolved  in  aqua  regia 
and  the  chloride  of  gold  solution  evaporated  to  dryness. 
Aluminium  powder  is  still  more  suitable  for  precipitating  the 


DEPOSITION    OF    GOLD.  443 

gold ;  the  excess  of  aluminium  is  dissolved  by  potash  or 
soda  lye. 

From  the  acid  mixtures  serving  for  mat  pickling  gold,  or 
for  stripping,  the  gold  is  precipitated  by  solution  of  sulphate 
of  iron  (copperas)  added  in  excess.  The  gold  present  is  pre- 
cipitated as  a  brown  powder  mixed  with  ferric  oxide.  This 
powder  is  filtered  off  and  treated  in  a  porcelain  dish  with  hot 
hydrochloric  acid,  which  dissolves  the  iron.  The  gold  which 
remains  behind  is  then  filtered  off,  and,  after  washing,  dis- 
solved in  aqua  regia  in  order  to  work  the  solution  into  ful- 
minating gold  or  neutral  chloride  of  gold. 

For  gilding  by  contact,  boiling  and  friction,  see  special  chap- 
ter "  Deposition  by  Contact." 


CHAPTER  X. 

DEPOSITION    OF    PLATINUM    AND    PALLADIUM. 
1.  DEPOSITION  OF  PLATINUM  (PT  =  195.2  PARTS  BY  WEIGHT). 

Properties  of  platinum. — Pure  platinum  is  white  with  a  gray- 
ish tinge.  It  is  as  soft  as  copper,  malleable  and  very  ductile. 
At  a  white  heat  it  can  be  welded,  but  is  fusible  only  with  the 
oxyhydrogen  blowpipe  or  by  the  electric  current.  Its  specific 
gravity  is  21.4. 

Air  has  no  oxidizing  action  upon  platinum.  It  is  scarcely 
acted  upon  by  any  single  acid  ;  prolonged  boiling  with  con- 
centrated sulphuric  acid  appears  to  dissolve  the  metal  slowly. 
The  best  solvent  for  it  is  aqua  regia,  which  forms  the  tetra- 
chloride,  PtCl4.  Chlorine,  bromine,  sulphur  and  phosphorus 
combine  directly  with  platinum,  and  fusing  saltpetre  and 
caustic  alkali  attack  it. 

Besides,  in  the  malleable  and  fused  state,  platinum  may  be 
obtained  as  a  very  finely  divided  powder,  the  so-called  plati- 
num black,  which  is  precipitated  with  zinc  from  dilute  solution 
of  platinum  chloride  acidulated  with  hydrochloric  acid. 

Platinum  baths. — In  view  of  the  valuable  properties  of  plat- 
inum of  oxidizing  only  under  certain  difficult  conditions,  of 
possessing  an  agreeable  white  color,  and  of  taking  a  fine 
polish,  it  seems  strange  that  greater  attention  has  not  been 
paid  to  the  electro-deposition  of  this  metal  than  is  actually 
the  case.  The  reason  for  this  may  perhaps  be  found  in  the 
fact  that  the  baths  formerly  employed  for  experiments  pos- 
sessed serious  defects,  causing  the  operator  many  difficulties,, 
and  besides,  allowed  only  of  the  production  of  thin  deposits. 
Giving  due  consideration  to  the  requirements  of  the  process 
of  electro-deposition  of  platinum,  and  with  the  use  of  a  suit- 

(444) 


DEPOSITION    OF    PLATINUM    AND    PALLADIUM.  445 

able  bath,  deposits  of  platinum  of  a  certain  thickness  can  be 
readily  produced,  and  necessary  conditions  will  be  described- 
under  "  Treatment  of  Platinum  Baths." 

The  platinum  baths  formerly  proposed  did  not  yield  satis- 
factory results,  because  the  content  of  platinum  was  too  small 
in  some  of  them,  while  with  others  dense  deposits  could  not  be 
obtained.  A  more  recent  formula  by  Bottger,  however,  gives 
quite  a  good  bath.  A  moderately  dilute,  boiling-hot  solution 
of  sodium  citrate  is  added  to  platoso-ammonium  chloride  until 
an  excess  of  the  latter  no  longer  dissolves,  even  after  continued 
boiling.  The  following  proportions  have  been  found  very 
suitable  :  Dissolve  17J  ozs.  of  citric  acid  in  2  quarts  of  water, 
and  neutralize  with  caustic  soda.  To  the  boiling  solution  add, 
whilst  constantly  stirring,  the  platoso-ammonium  chloride 
freshly  precipitated  from  2.64  ozs.  of  chloride  of  platinum, 
heat  until  solution  is  complete,  allow  to  cool,  and  dilute  with 
water  to  5  quarts.  To  decrease  the  resistance  of  the  bath,  0.7 
or  0.8  oz.  of  ammonium  chloride  may  be  added  ;  a  larger 
addition,  however,  will  cause  the  separation  of  dark-colored 
platinum. 

The  platoso-ammonium  chloride  is  prepared  by  adding  to  a 
concentrated  solution  of  platinic  chloride,  concentrated  solu- 
tion of  ammonium  chloride  until  a  yellow  precipitate  is  no 
longer  formed  on  adding  a  further  drop.  The  precipitate  is 
filtered  off  and  brought  into  the  boiling  solution  of  sodium 
-citrate.  The  bath  works  very  uniformly  if  the  content  of 
platinum  is  from  time  to  time  replenished. 

"The  Bright  Platinum  Plating  Company,"  of  London,  has 
patented  the  following  composition  of  a  platinum  bath  :  Chlor- 
ide of  platinum  0.98  oz.,  sodium  phosphate  19|  ozs.,  ammo- 
nium phosphate  3.05  ozs.,  sodium  chloride  0.98  oz.,  and  borax 
0.35  oz.,  are  dissolved,  with  the  aid  of  heat,  in  6  to  8  quarts  of 
water,  and  the  solution  is  boiled  for  10  hours,  the  water  lost 
by  evaporation  being  constantly  replaced.  The  results  ob- 
tained with  this  bath  were  not  much  better  than  with  Bottger's. 

Jordis  obtained  useful  results  from  a  platinum  lactate  bath 


446  ELECTRO-DEPOSITION    OF    METALS. 

prepared  by  transposition  from  platinic  sulphate  with  ammon- 
ium lactate.  There  are,  however,  difficulties  in  obtaining 
platinic  sulphate  of  uniform  composition.* 

Management  of  platinum  baths.  Copper  and  brass  may  be 
directly  plated  with  platinum,  but  iron,  steel  and  other  metals 
are  first  to  be  coppered,  otherwise  they  would  soon  decompose 
the  platinum  bath,  independent  of  the  fact  that  an  unexcep- 
tionable deposit  cannot  be  produced  upon  them  without  the 
cementing  intermediary  layer  of  copper. 

Platinum  baths  must  be  used  hot,  and  even  then  require  an 
electro-motive  force  of  5  to  6  volts,  and  hence,  in  plating  with 
a  battery  at  least  three,  or  better  four,  Bunsen  cells  must  be 
coupled  one  after  the  other.  An  abundant  evolution  of  gas 
must  appear  on  the  objects  and  anodes.  The  anode-surface 
(platinum  anodes)  must  not  be  too  small,  and  should  be  only 
at  a  few  centimeters'  distance  from  the  objects.  Since  the 
platinum  anodes  do  not  dissolve,  the  content  of  platinum  in 
the  bath  decreases  constantly,  and  the  bath  must  from  time  to 
time  be  strengthened.  For  this  purpose,  the  bath,  prepared 
according  to  Bottger's  formula,  is  heated  in  a  porcelain  dish 
or  enameled  vessel  to  the  boiling-point,  a  small  quantity  of 
fresh  solution  of  sodium  citrate  is  added  and  platoso-ammon- 
ium  chloride  introduced  so  long  as  solution  takes  place.  A 
concentrated  solution  of  platoso-ammonium  chloride  in  sodium 
citrate  (so-called  platinum  essence)  may  be  kept  on  hand  and 
a  small  quantity  of  it  be  at  intervals  added  to  the  bath.  Baths 
prepared  according  to  the  English  method  are  strengthened 
by  the  addition  of  platinum  chloride. 

Execution  of  platinum  plating.  The  objects,  thoroughly  freed 
from  grease  and,  if  necessary,  coppered,  are  suspended  in  the 
bath  heated  to  between  176°  and  194°  F.,  and  this  tempera- 
ture must  be  maintained  during  the  entire  operation.  The 
current  should  be  of  sufficient  strength  and  the  anodes  placed 
so  close  to  the  objects  that  a  liberal  evolution  of  gas  appears 

*  Jordis,  Die  Elektrolyse  wasseriger  Metallsalzlosungen,  1901. 


DEPOSITION    OF    PLATINUM    AND    PALLADIUM.  447 

on  them.  For  plating  large  objects,  it  is  recommended  to  go- 
round  them,  at  a  distance  of  0.31  to  0.39  inch,  with  a  hand- 
anode  of  platinum  sheet  which  should  not  be  too  small  and 
should  be  connected  to  the  anode-rod.  When  the  current  has- 
vigorously  acted  for  8  to  10  minutes,  the  objects  are  taken 
from  the  bath,  dried  and  polished.  However,  for  the  produc- 
tion of  heavy  deposits — for  instance,  upon  points  of  lightning 
rods — the  deposit  is  vigorously  brushed  with  a  steel-wire 
scratch-brush  or  fine  pumice-powder.  The  objects  are  then 
once  more  freed  from  grease  and  returned  for  10  or  15  minutes 
longer  to  the  bath  to  receive  a  further  deposit  of  platinum 
with  a  weaker  current,  which  must,  however,  be  strong  enough 
to  cause  the  escape  of  an  abundance  of  gas-bubbles.  The 
objects  are  then  taken  out,  and  after  immersion  in  hot  water, 
dried  in  sawdust.  The  deposit  is  then  well  burnished,  first 
with  the  steel  tool  and  finally  with  the  stone,  whereby  the 
gray  tone  disappears  and  the  deposit  shows  the  color  and 
luster  of  massive  platinum  sheet.  Points  of  lightning-rods 
platinized  in  this  manner  were  without  flaw  after  an  ex- 
posure to  atmospheric  influences  for  more  than  six  years. 

For  plating  directly,  without  previous  coppering,  iron,, 
nickel,  cobalt  and  their  alloys  with  platinum,  the  following 
process  has  been  patented  in  Germany  :  *  Nickel  or  cobalt  is- 
first  electrolytically  deposited  upon  base  metals  fusing  with 
difficulty,  such  as,  iron,  nickel,  cobalt,  or  their  alloys,  for 
instance,  nickel  steel,  a  suitable  bath  for  this  purpose  being 
composed  of  nickel-ammonium  sulphate  290  parts,  ammonium 
sulphate  75,  citric  acid  20,  distilled  water  4000.  The  metal 
is  then  heated  in  a  reducing  hydrogen  atmosphere  at  1652° 
to  1832°  F.,  this  operation  being  repeated  after  each  elec- 
trolytical  treatment  in  the  platinum  bath.  The  latter  is  best, 
composed  of:  Platinum-ammonium  phosphate  25  parts, 
sodium  phosphate  500,  distilled  water  4000. 

The  advantage  claimed  for  this  process  is  that  the  deposit. 

*  German  patent  201664. 


448  ELECTRO-DEPOSITION    OF    METALS. 

of  platinum  does  not  peel  off  even  when  exposed  to  great  heat, 
as  is  the  case  with  an  alloy  previously  coppered,  and  that  by 
frequently  repeating  the  operation  the  content  of  platinum 
steadily  increases  until  the  deposit  finally  possesses  the  prop- 
erties of  pure  platinum. 

Recovery  of  platinum  from  platinum  solutions.  From  not  too 
large  baths,  precipitation  of  the  platinum  with  sulphuretted 
hydrogen  is  the  rnost  suitable  method,  and  preferable  to  evap- 
orating and  reducing  the  metal  from  the  residue.  The  pro- 
cess is  as  follows  :  Acidulate  the  platinum  solution  with  hydro- 
chloric acid ;  and,  after  warming  it,  conduct  sulphuretted 
hydrogen  into  it.  The  metal  (together  with  any  copper  pres- 
ent) precipitates  as  sulphide  of  platinum.  The  precipitate  is 
filtered  off.  dried,  and  ignited  in  the  air,  whereby  metallic 
platinum  remains  behind.  From  larger  baths  the  platinum 
may  be  precipitated  by  suspending  bright  sheets  of  iron  in  the 
acidulated  bath.  In  both  cases  the  precipitated  platinum  is 
'treated  with  dilute  nitric  acid  in  order  to  dissolve  any  copper 
present.  After  filtering  off  and  washing  the  pure  platinum, 
-dissolve  it  in  aqua  regia.  The  solution  is  then  evaporated  to 
-dryness  in  the  water  bath,  and  the  chloride  of  platinum  thus 
obtained  may  be  used  in  making  a  fresh  bath.  Precipitation 
by  zinc  sheets  or  zinc  dust  can  also  be  recommended. 

2.     DEPOSITION  OF  PALLADIUM. 

Properties  of  palladium.  Palladium,  when  compact,  has  a 
white  color  and  possesses  a  luster  almost  equal  to  that  of  sil- 
Ter.  Its  specific  gravity  is  about  12.0  ;  it  is  malleable  and 
•ductile,  and  may  be  fused  at  a  white  heat.  In  the  oxy- 
hydrogen  flame  it  is  volatilized,  forming  a  green  vapor.  It  is 
less  permanent  in  the  air  than  platinum.  It  is  dissolved  by 
nitric  acid  ;  it  is  scarcely  attacked,  however,  by  hydrochloric 
or  sulphuric  acid.  Hydriodic  acid  and  free  iodine  coat  it 
with  the  black  palladium  iodide. 

On  account  of  the  high  price  of  its  salts,  palladium  has  been 
<but  little  used  for  electro-plating  purposes ;  nor,  for  the  same 


DEPOSITION    OF    PLATINUM    AND    PALLADIUM.  449 

reason,  is  it  likely  to  be  more  extensively  employed  in  the 
future. 

According  to  M.  Bertrand,  the  most  suitable  bath  consists  of 
a  neutral  solution  of  the  double  chloride  of  palladium  and 
ammonium,  which  is  readily  decomposed  by  3  Bunsen  cells 
coupled  one  behind  the  other  (therefore  about  5.4  volts).  A 
sheet  of  palladium  is  used  as  anode. 

A  solution  of  palladium  cyanide  in  potassium  cyanide  does 
not  yield  as  good  results  as  the  above  bath. 

Palladium  is  entirely  constant  in  the  air,  and  in  color 
closely  resembles  silver.  It  possesses  further  the  property  of 
not  being  blackened  by  sulphuretted  hydrogen,  and  for  this 
reason  it  is  sometimes  employed  for  coating  silver-plated 
metallic  articles. 

Palladium  has  also  of  recent  years  been  employed  for 
plating  watch  movements.  According  to  M.  Pilet,  4  milli- 
grammes (about  iV  grain)  of  palladium  are  sufficient  to  coat 
the  works  of  an  ordinary-sized  watch.  M.  Pilet  recommends 
the  following  bath  :  Water  2  quarts,  chloride  of  palladium  5J 
drachms,  phosphate  of  ammonia  3J  ozs.,  phosphate  of  soda 
17J  ozs.,  benzoic  acid  2f  drachms. 

Deposits  of  iridium  and  rhodium  have  recently  been  pro- 
duced from  baths  similar  in  composition  to  those  mentioned 
under  palladium.  But  as  these  metals  would  be  used  for 
plating  purposes  only  in  isolated  cases,  it  is  not  necessary  to 
enter  into  details. 
29 


CHAPTER  XL 

DEPOSITION  OF  TIN,  ZINC,  LEAD  AND  IRON, 
i.  DEPOSITION  OF  TIN  (Sn  =  119  parts  by  weight). 

Properties  of  tin.  Tin  is  a  white,  highly  lustrous  metal.  It 
possesses  but  little  tenacity,  but  has  a  high  degree  of  mallea- 
bility, and  tin-foil  may  be  obtained  in  leaves  less  than  ^\ih 
of  a  millimeter  in  thickness.  Tin  melts  at  about  446°  F., 
and  evaporates  at  a  high  temperature.  The  fused  metal  shows 
great  tendency  to  crystallize  on  congealing.  By  treating  the 
surface  of  melted  tin  with  a  dilute  acid,  the  crystalline  struc- 
ture appears  in  designs  (moire  metallique),  resembling  the  ice- 
flowers  on  frosted  windows. 

Tin  remains  quite  constant  even  in  moist  air,  and  resists 
the  influence  of  an  atmosphere  containing  sulphuretted  hy- 
drogen. Strong  hydrochloric  acid  quickly  dissolves  tin  on 
heating,  hydrogen  being  evolved  and  stannous  chloride 
formed.  Dilute  sulphuric  acid  has  but  little  action  on  the 
metal ;  when  heated  with  concentrated  sulphuric  acid,  sulphur 
dioxide  is  evolved.  Dilute  nitric  acid  dissolves  tin  in  the 
cold  without  evolution  of  gas ;  concentrated  nitric  acid  acts 
vigorously  upon  the  metal,  whereby  oxide  of  tin,  which  is 
insoluble  in  the  acid,  is  formed.  Alkaline  lyes  dissolve  the 
metal  to  sodium  stannate,  hydrogen  being  thereby  evolved. 

Tin  baths.  The  bath  used  by  Roseleur  for  tinning  with  the 
battery  works  very  well.  It  is  composed  as  follows : 

I.  Pyrophosphate  of  soda  3.5  ozs.,  tin  salt  (fused)  0.35  oz.> 
water  10  quarts. 

Electro-motive  force  at  10  cm.  electrode-distance,  1.25  volts. 

Current  density,  0.25  ampere. 

To  prepare  the  bath  dissolve  the  pyrophosphate  of  soda  in 

(450) 


DEPOSITION    OF    TIN,  ZINC,  LEAD    AND    IRON.  451 

10  quarts  of  rain  water,  suspend  the  tin-salt  in  a  small  linen 
bag  in  the  solution,  and  move  the  bag  to  and  fro  until  its 
contents  are  entirely  dissolved. 

Objects  of  zinc,  copper  and  brass  are  directly  tinned  in  this 
bath.  Articles  of  iron  and  steel  are  first  coppered  or  prelimi- 
narily tinned  by  boiling  in  a  bath  given  later  on  under  tinning 
by  contact,  the  deposit  of  tin  being  then  augmented  in  bath  I 
with  the  battery  current.  Cast- tin  anodes  as  large  as  possible 
are  used,  which,  however,  will  not  keep  the  content  of  tin  in 
the  bath  constant.  It  is  therefore  necessary,  from  time  to 
time,  to  add  tin-salt,  which  is  best  done  by  preparing  a  solu- 
tion of  3.5  ozs.  of  pyrophosphate  of  soda  in  1  quart  of  water 
and  introducing  into  the  solution  tin-salt  as  long  as  the  latter 
dissolves  clear.  Of  this  tin-essence  add  to  the  bath  more  or 
less,  as  may  be  required,  and  also  augment  the  content  of 
pyrophosphate  of  soda,  if  notwithstanding  the  addition  of  tin- 
salt,  the  deposition  of  tin  proceeds  sluggishly. 

Though  the  bath  composed  according  to  formula  I  suffices 
for  most  purposes,  an  alkaline  tin  bath,  first  proposed  by 
Eisner,  and  later  on  recommended  by  Maistrasse,  Fearn,  Birg- 
ham  and  others,  with  or  without  addition  of  potassium  cyan- 
ide, may  be  mentioned  as  follows : 

II.  Crystallized  tin-salt  0.7  ozs.,  water  1  quart,  and  potash 
lye  of  10°  Beaum£  until  the  precipitate  formed  dissolves. 

As  seen  from  the  formula  the  solution  of  tin-salt  is  com- 
pounded with  potash  lye  of  the  stated  concentration  (or  with 
a  solution  of  1  oz.  of  pure  caustic  potash  in  water),  until  the 
precipitate  of  stannous  hydrate  again  dissolves. 

Some  operators  recommend  the  addition  of  0.35  oz.  of  potas- 
sium cyanide  to  the  solution. 

In  testing  Salzede's  bronze  bath  (p.  363),  it  was  found  to 
yield  quite  a  good  deposit  of  tin  directly  upon  cast  iron,  and  it 
was  successfully  used  for  this  purpose  by  omitting  the  cuprous 
chloride,  and  using  instead  0.88  oz.  of  stannous  chloride,  so 
that  the  composition  became  as  follows : 

Ila.  98  per  cent,  potassium  cyanide  3.5  ozs.,  carbonate  of 


452  ELECTRO-DEPOSITION    OF    METALS. 

potassium  35J  ozs.,  stannous  chloride  0.88  ozs.,  water  10 
quarts.  With  4  volts  a  heavy  deposit  was  rapidly  obtained. 

Very  good  results  were  obtained  in  a  hot  bath  (158°  to  194° 
F.),  first  made  public  by  Neubeck,  which  consists  of: 

III.  70  per  cent,  caustic  soda  35J  ozs.,  ammonium  soda 
35  J  ozs.,  fused  tin-salt  7  ozs.,  water  10  quarts. 

Electro-motive  force  at  10  cm.  electrode-distance,  and  155° 
F.,  0.8  volt. 

Current-density  1  ampere. 

The  chemicals  are  sufficiently  dissolved  in  the  water. 
When  the  bath  commences  to  work  sluggishly,  about  0.35  to 
0.5  oz.  of  fused  tin-salt  has  to  be  added. 

Management  of  tin  baths. — Tin  baths  should  not  be  used  at 
a  temperature  below  68°  F.  Too  strong  a  current  causes  a 
spongy  reduction  of  the  tin,  which  does  not  adhere  well,  while 
with  a  suitable  current-strength  quite  a  dense  and  reguline 
deposit  is  obtained.  Cast-tin  plates,  with  as  large  a  surface  as 
possible,  are  used  as  anodes.  The  choice  of  the  tin-salt  exerts 
some  influence  upon  the  color  of  the  tinning.  By  using,  for 
instance,  crystallized  tin-salt,  which  is  always  acid,  in  prepar- 
ing the  bath  according  to  formula  I,  a  beautiful  white  tinning 
with  a  bluish  tinge  is  obtained,  which,  however,  does  not 
adhere  so  well  as  that  produced  with  fused  tin-salt.  Again, 
the  latter  yields  a  somewhat  dull  gray  layer  of  tin,  and  there- 
fore the  effects  of  the  bath  will  have  to  be  corrected  by  the 
addition  of  one  or  the  other  salt. 

As  previously  mentioned,  iron  and  steel  objects  are  best  sub- 
jected to  a  light  preliminary  tinning  by  boiling.  However, 
instead  of  this  preliminary  tinning,  they  may  first  be  electro- 
coppered  and,  after  scratch-brushing  the  copper  deposit, 
brought  into  the  tin  bath. 

Process  of  tin-plating. — From  what  has  been  said,  it  will  be 
evident  that  the  execution  of  tin-plating  is  simple  enough. 
After  being  freed  from  grease,  and  pickled,  the  objects  are 
brought  into  the  bath  and  plated  with  a  weak  current.  For 
heavy  deposits  the  objects  are  frequently  taken  from  the  bath 


DEPOSITION    OF    TIN,  ZINC,  LEAD    AND    IRON.  453 

and  thoroughly  brushed  with  a  brass  scratch-brush,  not  too 
hard,  and  moistened  with  dilute  sulphuric  acid  (1  part  acid 
of  66°  Be.  to  25  water)  and,  after  rinsing  in  water,  are  re- 
turned to  the  bath.  If,  with  the  use  of  too  strong  a  current, 
the  color  of  the  deposit  is  observed  to  turn  a  dark  dull  gray, 
scratch-brushing  must  be  repeated.  When  the  tinning  is 
finished  the  articles  are  brushed  with  a  brass  scratch-brush 
and  decoction  of  soap-root,  then  dried  in  sawdust,  and  polished 
with  fine  whiting. 

For  tinning  by  contact  and  boiling,  see  special  chapter,  "  Depo- 
sitions by  Contact." 

2.     DEPOSITION  OF  ZINC  (Zn  —  65.37  parts  by  weight). 

Properties  of  Zinc.  Zinc  is  a  bluish-white  metal,  possessing 
high  metallic  luster.  It  melts  at  776°  F.  At  the  ordinary 
temperature  zinc  is  brittle,  but  it  is  malleable  at  between  212° 
and  300°  F.,  and  can  be  rolled  into  sheets.  At  392°  F.  it 
again  becomes  brittle,  and  may  be  readily  reduced  to  powder. 
The  specific  gravity  of  zinc  varies  from  about  6.86  to  7.2. 
When  strongly  heated  in  the  air,  or  in  oxygen,  it  burns  with 
a  greenish-white  flame,  producing  dense  white  fumes  of  the 
oxide. 

In  moist  air  it  becomes  coated  with  a  thin  layer  of  basic 
carbonate,  which  protects  the  metal  beneath  from  further 
oxidation.  Pure  zinc  dissolves  slowly  in  the  ordinary  mineral 
acids,  but  the  commercial  article  containing  foreign  metals  is 
rapidly  attacked,  hydrogen  being  evolved. 

Since  zinc  is  a  very  electro-positive  metal  and  precipitates 
most  of  the  heavy  metals  from  their  solutions,  especially  cop- 
per, silver,  lead,  antimony,  arsenic,  tin,  cadmium,  etc.,  this 
being  the  reason  why  in  dissolving  impure  zinc,  the  admixed 
metals  do  not  pass  into  solution  so  long  as  zinc  in  excess  is 
present.  Potash  and  soda  lyes  attack  zinc,  especially  when  it 
is  in  contact  with  a  more  electro-negative  metal,  hydrogen 
being  evolved. 

Zinc  in  contact  with  iron  protects  the  latter  from  rust,  and 
also  prevents  copper  from  dissolving  when  in  contact  with  it. 


454  ELECTRO-DEPOSITION    OF    METALS. 

Up  to  within  a  few  years,  objects  were,  as  a  rule,  zincked 
by  the  so-called  galvanizing  process,  and  electro-plating  with 
zinc  was  only  used  for  parts  which  could  not  stand  hot  gal- 
vanizing, for  instance,  finer  qualities  of  cast-iron  objects  or 
parts  of  machines,  such  as  parts  of  centrifugals  for  sugar 
houses. 

Further  researches  and  practical  experience  in  this  line  led 
to  the  application  of  zinc  by  the  electrolytic  cold  process  to 
other  objects,  such  as  sheet-iron  and  iron  for  constructive  pur- 
poses. Thus,  for  instance,  all  the  iron  in  lengths  of  up  to  36 
feet  and  7  feet  6  inches  projection  used  in  the  construction  of 
the  palm  houses  in  the  new  botanical  garden  at  Dahmen- 
Berlin  were  electro-plated  with  a  thick  deposit  of  zinc,  and 
thorough  investigations  by  the  authorities  have  shown  that, 
as  regards  protection  from  rust,  the  iron  thus  plated  with  zinc 
is  at  least  not  inferior  to  iron  zincked  by  the  hot  process. 

Electro-zincking  has  also  proved  of  value  for  protecting  the 
tubes  of  the  Thornycroft  boiler  and  several  plants  of  this  char- 
acter are  now  in  operation.  Of  great  importance  is  also  the 
electro-zincking  of  iron  and  steel  network  for  corsets. 

Electro-zincking  is  also  of  great  advantage  for  small  iron 
articles,  for  instance,  screws  and  nuts,  since  the  worms  do  not 
fill  up  with  metal,  as  is  the  case  in  the  hot  process,  and  con- 
sequently do  not  require  re-cutting. 

While  in  the  further  manipulations,  such  as  bending, 
punching,  etc.,  of  sheets,  angle-iron,  "f-iron,  pipes,  etc., 
zincked  by  the  hot  galvanizing  process,  the  layer  of  zinc 
readily  cracks  off,  the  electro-deposit  adheres  very  firmly,  if 
the  basis-metal  has  been  properly  cleansed ;  and  if  the  de- 
posit is  not  of  excessive  thickness,  which  would  be  entirely 
useless,  it  cannot  be  detached  by  bending  and  beating.  If  it 
be  further  taken  into  consideration  that  in  zincking  by  the 
hot  galvanizing  process  much  more  zinc  than  is  necessary  for 
the  protection  against  rust  adheres  to  the  objects,  that  the  loss 
of  zinc  by  the  formation  of  hard  zinc  (an  iron-zinc  alloy)  is 
considerable,  and  that  it  is  quite  expensive  to  keep  the  plant 


DEPOSITION    OF    TIN,  ZINC,  LEAD    AND    IRON.  455 

in  repair,  it  will  have  to  be  admitted  that  in  an  economical 
aspect  also,  zincking  with  the  assistance  of  the  current  pre- 
sents many  advantages. 

Exhaustive  comparative  experiments  regarding  zincking  by 
the  hot  process  and  by  electro-deposition  (cold  process),  have 
been  published  by  Burgess.*  These  experiments  relate  to  the 
•duration  of  protection  of  the  basis-metal,  adhering  power  of 
the  zinc  coating,  ductility  and  flexibility  of  the  latter,  uni- 
formity of  the  coatings  as  regards  strength  and  density,  as 
well  as  resistance  against  mechanical  wear.  The  results  of 
the  experiments  were  as  follows : 

The  disadvantages  of  hot  galvanizing  are :  Considerable 
•consumption  of  heat  and  a  material  loss  of  zinc  by  oxidation 
on  the  surface  of  the  fused  zinc,  by  alloying  with  the  cover  of 
sal-ammoniac,  and  by  the  formation  of  hard  zinc — a  zinc-iron 
alloy  which  is  formed  at  the  expense  of  the  walls  of  the  iron 
tank.  Burgess  estimates  the  loss  of  zinc  at  50  per  cent,  of  the 
zinc  used,  and  only  a  portion  of  it  can  be  regained  by  a  special 
process. 

On  the  other  hand,  in  electro-zincking  no  loss  by  heat  is 
incurred,  and  hence  such  articles  as  steel-wire,  steel-springs, 
•etc.,  can  be  zincked,  the  treatment  of  which,  at  the  tempera- 
ture of  the  melted  zinc,  would  be  out  of  the  question.  Elec- 
tro-zincking of  certain  kinds  of  work  is  now  specified  by  the 
Governments  of  'Great  Britain  and  Germany,  and  the  United 
States  Government  has  installed  at  its  various  shipyards  com- 
plete equipments  for  the  purpose  of  treating  articles  by  the 
-electrical  method. 

The  loss  of  zinc  in  electro-zincking  is  nominal  and  the  wear 
of  the  vessels  used  is  less  than  10  per  cent,  per  annum,  while 
in  the  hot  process  it  amounts  to  from  50  to  100  per  cent. 

By  electro-deposition  articles  of  any  size  may  be  zincked  ; 
the  bath  is  always  ready  for  use,  and  the  thickness  of  the  coat- 
ing can  be  controlled  and  regulated,  which  in  hot  galvanizing 

*Lead  and  Zinc  News,  1904,  viii,  Nos.  8  to  10. 


456  ELECTRO-DEPOSITION    OF    METALS. 

is  possible  only  to  a  limited  degree.  Both  processes  possess 
the  drawback  of  never  yielding  coatings  of  uniform  thickness  ; 
the  edges  of  hot-zincked  pieces,  especially  of  those  which 
come  last  from  the  bath,  are  smeared  over,  i.  e.,  they  are  more 
heavily  zincked  than  others,  while,  by  reason  of  the  current- 
density  being  greater  on  these  portions,  the  edges  of  sheets- 
zincked  by  electro-deposition  are  also  more  heavily  zincked 
than  parts  in  the  center  of  the  sheets. 

The  usual  method  of  determining,  by  immersion  in  a  20  per 
cent,  copper  sulphate  solution,  the  thickness  of  the  coating  of 
zinc  obtained  by  hot-galvanizing,  was  found  by  Burgess  to 
be  quite  unsuitable  for  judging  the  thickness  and  quality  of 
electro-zincking.  This  test,  known  as  Preece's  test,  consists 
in  placing  the  galvanized  iron  in  the  copper  solution  for  J  to 
1  minute,  and  continuing  the  immersions  until  the  test-piece 
shows  a  red  deposit  of  copper,  which  is  a  true  indication  that 
the  zinc  has  been  penetrated  and  the  iron  exposed.  In  Ger- 
many it  is  as  a  rule  required  that  hot-galvanizing  must  stand 
for  at  least  30  seconds  constant  immersion  before  the  red  cop- 
per color  appears ;  so  long  as  the  coating  of  zinc  is  intact  there 
is  only  a  black  coloration.  On  applying  Preece's  test  to  elec- 
tro-zincked  articles  it  was  found  that  they  would  not  stand  as> 
many  immersions  in  the  copper  solution  as  coatings  obtained 
by  hot-galvanizing,  but  nevertheless  they  were  more  resisting 
to  atmospheric  influences.  For  testing  the  power  of  resistance- 
of  the  coatings,  Burgess  therefore  made  use  of  dilute  sulphuric 
acid,  and  found  that  an  electro-deposited  coating  J  the  weight 
of  one  produced  by  hot-galvanizing  possesses  the  same  power 
of  resisting  corrosion  as  the  latter,  and  that  for  coatings  of 
equal  thickness  the  proportion  of  the  resisting  power  is  as 
10  : 1.  This  superiority  of  electro-zincking  has  to  be  ascribed 
to  the  greater  purity  of  the  deposit  effected  by  electro- 
deposition. 

On  measuring  the  adhesive  power,  Burgess  ascertained  quite- 
different  values  from  those  of  hot-galvanizing.  With  electro- 
deposited  zinc  the  force  required  to  tear  the  coatings  from  the- 


DEPOSITION    0~P    TIN,  ZINC,  LEAD    AND    IRON.  457 

basis-metal  (iron)  amounted  on  an  average  to  482  Ibs.  per 
square  inch,  and  only  to  280  Ibs.  for  coatings  obtained  by 
hot-galvanizing.  Hence  the  adhesive  power  of  electro- 
deposited  coatings  is  materially  greater. 

Attempts  were  made  to  ascertain  the  ductility  and  flexibility 
of  the  coatings  by  rolling.  However,  no  positive  results  were 
obtained,  some  deposits  becoming  thereby  more  or  less  cracked, 
while  others  remained  intact.  The  flexibility  of  the  deposit  is- 
without  doubt  affected  by  the  reaction  of  the  bath,  and  it  has 
been  observed  that  from  very  slightly  acid  electrolytes,  with 
an  electro-motive  force  of  1.5  amperes,  deposits  free  from  cracks 
were  obtained  while  very  brittle  deposits  were  obtained  from 
more  strongly  acid  solution  with  the  same  current-density. 
Burgess's  experiments  in  this  respect  only  made  sure  of  the 
fact  that  there  is  no  material  difference  in  the  behavior  of 
hot-  and  cold-galvanized  sheets  with  coatings  of  equal  thick- 
ness. In  all  cases  the  zinc,  when  subjected  to  rolling,  showed 
a  tendency  to  separate  from  the  basis-metal;  the  zinc  detached, 
from  electro-zincked  sheet,  however,  possessed  greater  strength 
and  was  less  brittle  than  that  from  hot-galvanized  sheet. 

On  examining  the  detached  coatings  under  the  microscope- 
it  was  further  found  that,  contrary  to  the  generally  accepted; 
opinion,  the  coating  produced  by  hot-galvanizing  was  far  more 
porous  than  that  obtained  by  electro-deposition.  An  electro- 
deposit  of  less  than  100  grammes  zinc  per  square  meter  sur- 
face, was  to  be  sure  also  porous,  but  with  a  thickness  of  200- 
grammes  zinc  per  square  meter  the  pores  had  grown  together. 

The  resistance  against  mechanical  wear  was  apparently 
the  same  with  the  different  deposits  of  equal  thickness.  Only 
in  one  case  the  electro-deposit  proved  of  less  value  than  the- 
hot-galvanizing,  namely,  when  electro-zincked  sheets  were 
subjected  by  heating  and  cooling  to  frequent  and  considerable 
changes  in  temperature,  blisters  were  more  frequently  formed, 
and  the  zinc  became  detached  to  a  greater  extent  than  was 
the  case  with  hot-galvanized  sheet.  This  shows  that  electro- 
zincked  sheets  should  not  be  used  for  heating  pipes  for  higb 


458  ELECTRO-DEPOSITION    OF    METALS. 

'temperatures.  Blistering  is  less  to  be  feared  with  tempera- 
tures not  exceeding  that  of  steam  of  3  atmospheres. 

Zinc  baths.  While  flat  articles  can  be  readily  coated  with 
a  firmly-adhering  layer  of  zinc  of  uniform  thickness,  the  pro- 
duction of  such  a  deposit  upon  large,  shaped  articles  and  pro- 
filed objects  is  attended  with  difficulties,  because  zinc  baths  do 
not  work  quite  well  in  the  deeper  portions.  As  will  be  seen 
later  on,  these  difficulties  may  be  overcome,  on  the  one  hand, 
by  heating  the  baths  and,  on  the  other,  by  the  use  of  anodes 
with  somewhat  the  same  profile  as  the  article  to  be  zincked, 
so  that  all  portions  of  it  are  as  nearly  as  possible  at  the  same 
^distance  from  the  anodes. 

In  plating  articles  with  depressions,  better  results  are  ob- 
tained by  depositing  not  pure  zinc,  but  zinc  in  combination 
with  other  metals.  Of  course,  zinc  must  be  largely  in  excess 
if  the  deposit  is  to  have  the  same  effect  as  pure  zinc  in  pro- 
tecting the  plated  article  from  rust.  By  the  addition  of  salts 
of  magnesium  and  aluminium  to  the  zinc  bath,  Schaag,  Dr. 
Alexander  and  others  have  endeavored  to  deposit  zinc  in  com- 
bination with  these  metals.  While  the  possibility  of  deposit- 
ing aluminium  from  aqueous  solutions  is  doubtful,  it  is  very 
likely  that  in  Schaag's,  as  well  as  in  Dr.  Alexander's  patented 
process  neither  the  magnesium  nor  the  aluminium  is  the 
effective  agent,  but  the  tin  or  mercury  salts  which  are  also 
added  to  the  bath.  But  such  additions  are  nothing  new,  since 
deposits  of  zinc-tin  alloys  with  or  without  mercury  salts  have 
for  many  years  been  produced.  The  same  object  is  attained 
by  an  addition  of  tin  and  nickel  to  the  zinc  bath,  and  experi- 
ments have  conclusively  shown  that  deposits  upon  iron  pro- 
duced in  such  a  bath  protect  the  iron  from  rust  as  well  as  a 
deposit  produced  in  a  bath  of  pure  zinc,  or  in  Dr.  Alexander's 
zinc  baths,  the  patents  for  which  are  now  expired.  The  good 
effect  of  aluminium  sulphate  in  zinc  baths  might  solely  be 
due  to  the  fact  that  the  acidity  of  the  baths  is  longer  main- 
•tained. 

In  connection  with  the  Alexander  patent  it  may  here  be 


DEPOSITION    OF    TIN,  ZINC,  LEAD    AND    IRON.  459 

stated  that  an  important  decision  was  rendered  by  Judge 
Cross  of  the  Circuit  Court  of  the  United  States  for  the  District 
of  New  Jersey,  in  favor  of  the  Hanson  &  Van  Winkle  Co.,  of 
Newark,  N.  J.,  and  Chicago,  111.,  and  against  the  United  States 
Electro-Galvanizing  Co.  of  Brooklyn,  owners  of  these  patents. 
The  decision  ends  as  follows :  "  For  the  following,  among 
other  reasons,  then,  the  defendant  does  not  infringe ;  it  does 
not  make  the  alloyed  coating  of  the  patent,  employs  no  basic 
salts,  but  rather  makes  and  maintains  throughout  an  acid 
bath  ;  does  not  use  chloride  of  aluminium  in  its  salts,  does  not 
use  any  organic  substance  with  its  salts  or  bath,  or  any  equiva- 
lent thereof,  and  its  bath  is  composed  in  part  of  different  in- 
gredients from  the  complainants,  is  prepared  differently  and 
under  different  conditions,  and  its  ingredients,  in  so  far  as  they 
are  the  same,  appear  in  the  different  proportions.  The  bill  of 
complaint  will  accordingly  be  dismissed,  with  costs." 

Whatever  may  be  said  of  the  validity  of  the  Alexander 
patents  as  against  others,  as  against  the  salts  and  processes  of 
the  Hanson  &  Van  Winkle  Co.,  the  patent  is  of  no  effect. 
The  largest  cold  galvanizers  of  this  country  have  been  fitted 
up  by  the  experts  of  this  company. 

While  the  protection  against  rust  of  deposits  from  alloy- 
baths  is  about  the  same  as  from  pure  zinc  baths,  the  use  of  the 
latter,  without  the  addition  of  foreign  metals  can  nevertheless 
be  recommended,  since  with  a  suitable  composition  of  the  bath 
and  proper  arrangement  of  the  anodes  perfect  zinc  deposits 
can  in  all  cases  be  obtained. 

During  the  last  few  years  several  investigations  regarding 
the  electrolysis  of  zinc  have  been  made  and  numerous  propo- 
sitions have  been  advanced,  but  space  will  not  permit  to  con- 
sider them  here.  According  to  0.  Hildebrand  very  satis- 
factory results  are  obtained  with  the  so-called  regenerative 
process,  a  lead  plate  being  used  as  anode  instead  of  a  zinc 
anode.  Solution  of  zinc  sulphate  in  water,  to  which  is  added 
a  small  quantity  of  sulphuric  acid,  is  employed  as  electrolyte. 
By  the  use  of  a  regenerative  vat  charged  with  zinc  dust,  the 


460  ELECTRO-DEPOSITION    OF    METALS. 

electrolyte  is  kept  constantly  in  circulation  and  regenerated 
by  coming  in  contact  with  the  zinc  dust  in  the  regenerative  vat. 

By  this  method  zinc  coatings  of  good  quality  are  obtained. 
The  deposit  is  almost  free  from  impurities,  adheres  firmly  to 
the  iron  and  is  more  uniform  than  that  obtained  by  the  hot 
galvanizing  process.  The  zinc  being  used  in,  the  form  of 
finely  divided  zinc  dust  the  electrolyte  comes  in  intimate  con- 
tact with  it  and  consequently  is  very  quickly  neutralized. 
Besides  the  drawbacks  connected  with  the  use  of  zinc  anodes 
are  avoided.  As  disadvantages  may  be  mentioned  the  con- 
siderably greater  electro-motive  force  required  with  the  use  of 
insoluble  lead  anodes  and  the  consequently  larger  cost  of 
current,  and  further,  the  operating  expenses  caused  by  the 
apparatus  forcing  the  bath-liquor  into  the  regenerating  vats. 

Dr.  Szirmay  and  von  Kollerich  want  to  add  solution  of 
magnalium  (aluminium-magnesium  alloy)  in  sulphuric  acid 
and  dextrose  to  white  vitriol  (zinc  sulphate)  solution.  In/ 
dissolving  magnalium,  aluminium  sulphate  and  magnesium 
sulphate  are  formed.  Neither  aluminium  or  magnesium  in 
watery  solutions  are  reducible  as  metals  by  the  current,  as 
they  oxidize  at  the  moment  of  reduction,  water  being  decom- 
posed. The  effect  of  the  aluminium  sulphate  with  its  acid 
reaction  is  simply  that  the  bath  does  not  readily  become  alka- 
line, while  the  magnesium  sulphate  acts  as  a  conducting  salt,, 
the  separated  magnesium -ions  of  it  causing  the  secondary  re- 
duction of  zinc  from  the  sulphate  solution.  The  addition  of 
carbohydrates  to  which  dextrose  belongs,  which  became 
known  through  the  English  patent  No.  12691,  1897,  is 
claimed  to  prevent  the  formation  of  sponge,  which,  however,, 
according  to  experiments  made  in  Dr.  Langbein's  laboratory, 
is  the  case  only  to  a  limited  extent.  An  addition  of  dextrose 
appears  to  have  the  further  effect  of  the  bath  working  better 
in  the  deeper  portions  and  the  deposits  turning  out  less 
tufaceous.  The  deposits  frequently  come  from  the  bath  with 
a  slight  luster,  this  being  especially  the  case  when  electrolysis 
is  for  some  time  continued  after  the  addition  of  the  dextrose. 


DEPOSITION    OF    TIN,  ZINC,  LEAD    AND    IRON.  461 

According  to  Goldberg  (German  patent  151336)  an  addi- 
tion of  pyridine  to  zinc  baths  is  claimed  to  effect  a  dense  de- 
posit of  zinc  of  a  beautiful  white  color  and  velvety  appearance. 
On  testing  this  process  these  claims  were  found  to  be  correct, 
and  furthermore  such  a  bath  works  better  in  the  depression. 

Classen  has  patented  the  addition  of  glucosides,  and  claims 
to  obtain  thereby  the  deposition  of  lustrous  zinc  coatings. 

The  reason  why  in  baths  of  the  compositions  formerly 
given,  actually  thick  deposits  without  showing  a  spongy 
structure  could  not  be  obtained,  is  found  in  the  fact  that  these 
baths  contained  too  little  metal  and  had  an  unsuitable,  gen- 
erally alkaline,  reaction.  Even  when  electrolysis  has  only 
been  carried  on  for  a  short  time,  alkaline  baths  do  not  yield 
a  coherent  and  purely  metallic  deposit  of  zinc,  a  basic  zinc 
oxide  being  reduced  together  with  the  metallic  zinc,  which 
readily  gives  rise  to  the  formation  of  sponge. 

The  formula  for  an  alkaline  zinc  bath,  namely,  3J  ozs.  of 
white  vitriol  dissolved  in  1  quart  of  water,  and  adding  potash 
lye  until  the  precipitated  zinc  hydroxide  is  again  dissolved, 
which  was  given  in  former  editions  of  this  work,  yields  quite 
fair  results.  This  bath  works  best  when,  in  place  of  potash 
or  soda  lye,  ammonia  is  used  for  precipitating  and  dissolving 
the  zinc  hydroxide,  and  the  bath  contains  a  large  excess  of 
ammonia.  Hence,  in  the  above-mentioned  formula,  the 
potash  lye  should  be  replaced  by  ammonia  and,  in  addition 
to  the  quantity  required  for  the  solution  of  the  precipitate 
formed,  enough  of  it  should  be  used  to  impart  to  the  bath  a 
strong  odor  of  ammonia.  However,  by  reason  of  this  odor  of 
ammonia,  the  operation  of  such  a  bath  becomes  disagreeable, 
and  even  injurious  to  health. 

In  order  to  force  the  bath  to  work  better  in  the  deeper 
portions,  mercury  salts  in  the  form  of  potassium-mercuric  cya- 
nide may  be  added  to  alkaline  baths.  It  must,  moreover,  be 
borne  in  mind  that  an  addition  of  mercury  is  of  advantage 
because  the  anodes  are  thereby  superficially  amalgamated  and 
kept  in  a  purely  metallic  state.  In  alkaline  zinc  baths  par- 


462  ELECTRO-DEPOSITION    OF    METALS. 

ticularly,  an  abundant  coat  of  zinc  hydroxide  is  formed  upon 
the  anodes,  and  because  this  coat  does  not  dissolve  to  the  same 
extent  as  it  is  formed,  it  has  to  be  frequently  removed  by 
mechanical  means. 

Below  formulas  for  zinc  baths  which  have  stood  the  test  for 
a  long  time  are  given. 

I.  Chemically  pure  crystallized  zinc  sulphate  44  Ibs.,  pure 
crystallized  sodium  sulphate  8.8  Ibs.,  chemically  pure  zinc 
chloride  2.2  Ibs.,  crystallized  boric  acid  1.1  Ibs.,  dissolved  in 
water  to  a  100-quart  bath. 

Electro-motive  force  at  10  cm.  electrode-distance  and  at  64.4° 
F.,  1.1,  1.5,  1.8,  2.2,  2.4,  2.7,  3.7  volts. 

Current-density  at  64.4°  F.,  0.55,  0.75,  0.95,  1.15,  1.25,  1.45, 
1.9  amperes. 

Electro-motive  force  at  10  cm.  electrode-distance  and  at  113° 
F.,  0.9,  1.05,  1.25,  1.40,  1.8,  2.0,  2.3,  3.5  volts. 

Current-density  at  113°  F.,  0.7,  0.8,  1.0,  1.1,  1.4,  1.55,  1.8, 
2.75  amperes. 

This  bath,  as  well  as  others  of  similar  composition,  will 
stand  considerably  higher  current-densities  if  provision  is 
made  for  vigorous  agitation  of  the  electrolyte.  If  agitation  is 
to  be  avoided,  an  increase  of  the  content  of  zinc  salt  and  boric 
acid  is  of  advantage. 

To  prepare  the  bath,  dissolve  the  zinc  sulphate,  the  zinc 
chloride  and  sodium  sulphate  (Glauber's  salt)  in  luke-warm 
water.  Heat  a  portion  of  this  fluid  to  about  194°  F.,  dissolve 
in  it  the  boric  acid,  and  mix  it  with  the  other  solution.  An 
addition  of  0.8  to  1  oz.  of  dextrose  per  quart  is  recommended. 

For  the  production  of  a  good  deposit  of  zinc  it  is  of  im- 
portance to  use  zinc  salts  free  from  other  rnetals,  it  having 
been  shown  that  a  content  of  foreign  metals,  especially  iron, 
causes  disturbances. 

The  reaction  of  the  bath  should  be  kept  slightly  acid,  so 
that  blue  litmus  paper  is  intensely  reddened,  but  congo  paper 
is  not  perceptibly  blued.  The  bath  gradually  loses  its  acid 
reaction  and  does  not  work  as  well,  the  deposit  becoming 


DEPOSITION    OF    TIN,  ZINC,  LEAD    AND    IRON.  463 

darker  instead  of  pale  gray,  and  inclining  towards  the  forma- 
tion of  sponge.  It  should  then  be  acidulated  by  the  addition 
of  pure  dilute  sulphuric  acid.  For  flat  objects  (sheets,  etc.} 
the  bath  may  be  used  cold,  but  for  profiled  objects,  such  as 
angle-iron,  beams,  etc.,  it  is  advisable  to  heat  it  between  104° 
and  122°  F. 

II.  Crystallized   sodium   citrate  5.5   Ibs.,  chemically  pure 
zinc  chloride  8.8  Ibs.,  pure  crystallized  ammonium  chloride 
6.6  Ibs.     Dissolve  with  water  to  a  100-quart  Nbath. 

Electro-motive  force  at  10  cm.  electrode-distance  and  at  64.4° 
F.,  0.8,  1.0,  1.5,  1.8,  2.2,  3.4  volts. 

Current-density  at  64.4°  F.,  0.7,  0.9,  1.4,  1.7,  1.9,  3.0  am- 
p£res. 

Electro-motive  force  at  10  cm.  electrode-distance  and  113°  F., 
0.8,  1.0,  1.5,  1.75,  2.5,  3.2  volts. 

Current-density  at  113°  F.,  1.0,  1.25,  1.9,  2.3,  3.2,  4.3  am- 
peres. 

The  bath  is  prepared  by  dissolving  the  constituents  in  the 
water,  which  should  not  be  too  cold  ;  best  luke-warm.  What 
has  been  said  under  formula  I  in  reference  to  the  reaction, 
also  applies  to  this  bath. 

III.  Wm.  Schneider*  recommends  a  bath  of  the  following, 
composition  :  Water  1  gallon,  sulphate  of  zinc  2  Ibs.,  sulphate 
of  aluminium  2  ozs.,  glycerine  J  oz.     Electro-motive  force:  10 
amperes  to  1  square  foot  of  surface.     The  work  must  be  agi- 
tated while  being  coated.     The  use  of  pure  zinc  anodes  is- 
imperatlve  if  satisfactory  results  are  to  be  obtained,  and  the 
iron  to  be  plated  must  be  perfectly  clean.     If  this  solution* 
is  carefully  attended  to  it  will  plate  a  good  light  gray,  and  by 
the  addition  of  a  few  of  the  various  reagents  of  which  there 
are  several,  such  as  glue  and  dextrine,  on  the  market,  a  very 
bright  deposit  of  zinc  can  be  obtained. 

Zinc  anodes.  Treatment  of  zinc  baths.  For  anodes  it  is  best 
to  use  very  pure  rolled-zinc  sheets  0.11  to  0.19  inch  or  more 

*  Metal  Industry,  No.  9,,  1909. 


464  ELECTRO-DEPOSITION    OF    METALS. 

in  thickness.  Strips  of  zinc  riveted  to  the  anodes  with  zinc 
rivets  serve  for  suspending  the  anodes  to  the  anode  rods.  For 
;zincking  sheet-iron,  wires,  etc.,  on  a  large  scale,  cast  zinc 
anodes  may  be  preferred  on  account  of  being  cheaper.  It 
must,  however,  be  borne  in  mind  that  cast  anodes  readily 
crumble,  especially  when  they  have  "frequently  to  be  cleansed 
mechanically  by  scraping  and  scratch-brushing  for  the  removal 
of  the  basic  zinc  salts  forming  on  them.  The  loss  of  zinc 
caused  by  the  formation  of  basic  zinc  salt  and  by  crumbling 
is  considerable,  and  according  to  Cowper-Coles  may  be  as 
large  as  30  per  cent,  of  the  entire  consumption  of  zinc.  This 
estimate,  however,  appears  to  be  excessive ;  to  be  sure  the 
formation  of  a  coat  on  the  anodes  as  well  as  the  crumbling  of 
the  anodes  is  disagreeable,  but  it  cannot  be  considered  a  direct 
loss  since  the  zinc  salt  as  well  as  the  detached  crumbs  of 
metal  can,  by  dissolving  in  sulphuric  acid,  be  converted  into 
zinc  sulphate,  and  the  latter  be  used  for  strengthening  the 
bath.  The  surface  of  the  anodes  should  be  as  large  as  possible. 
Rolled  anodes  also  become  readily  coated  with  a  layer  of  basic 
zinc  salt,  and  it  is  advisable  from  time  to  time  to  remove  this 
layer  by  scratch-brushing.  The  coating  thus  removed  may 
be  dissolved  in  dilute  sulphuric  acid  and  added  to  the  bath 
as  neutral  zinc  solution.  As  previously  mentioned,  the  zinc 
baths  should  show  a  perceptibly  acid  reaction  in  order  to 
avoid  as  much  as  possible  the  formation  of  sponge,  and  there- 
fore the  reaction  should  at  short  intervals  be  tested  and,  if 
necessary,  corrected  by  the  addition  of  dilute  sulphuric  acid. 

The  zinc  anodes  should  be  removed  from  the  bath  when 
the  latter  is  not  in  operation,  otherwise  the  free  acid  of  the 
bath  would  be  neutralized  by  the  solution  of  zinc  and  it  would 
have  to  be  again  acidified. 

Although  the  zinc  baths,  without  exception,  work  well  at  a 
temperature  of  64.4°  to  68°  F.  upon  flat  articles,  it  is  recom- 
mended, in  view  of  the  slight  electro-motive  force  required,  to 
keep  them  somewhat  warmer. 

For  zincking  strongly-profiled  objects  it  is  advisable  to  heat 


DEPOSITION    OF    TIN,  ZINC,  LEAD    AND    IRON.  465 

the  baths  to  between  104°  and  113°  F.,  since  at  a  higher 
temperature  the  deposit  penetrates  better  into  the  deeper  por- 
tions. Anodes  with  profiles  similar  to  those  of  the  objects  are 
used.  As  shown  by  the  current  conditions  given  with  the 
formulas  for  the  baths,  a  fixed  current-density  is  not  obligatory 
in  electro-zincking.  For  the  bath,  according  to  formula  I, 
1.25  to  1.5  amperes  may  be  designated  as  the  lowest  rational 
current-density,  at  which  5.29  to  6.34  ozs.  of  zinc  per  square 
meter  (10.76  square  feet)  are  in  one  hour  deposited.  With 
heated  and  agitated  baths,  the  maximum  current-density  may 
be  given  as  about  3  amperes,  with  which  12.91  ozs.  of  zinc  per 
square  meter  are  in  one  hour  deposited.  However,  in  certain 
xBases,  this  current-density  may  be  exceeded.  For  baths,  ac- 
cording to  formula  II,  it  is  best  to  use  a  slighter  current- 
density.  Should  it,  however,  be  necessary  to  work  with 
higher  current-densities,  provision  has  to  be  made  for  a  suffi- 
ciently acid  reaction  and  thorough  agitation  in  order  to  avoid 
the  formation  of  sponge.  In  zincking,  agitation  of  the  baths 
is  of  special  value,  and,  if  possible,  should  never  be  omitted. 

Tanks  for  zinc  baths. — For  smaller  baths  it  is  best-  to  use 
stoneware  vessels,  while  for  larger  baths,  tanks  of  pitch-pine, 
or  still  better,  of  wood  lined  with  lead,  may  be  employed. 
Zinc  salt  solutions  gradually  impair  the  swelling  capacity  of 
wood,  and  even  pitch-pine  tanks,  most  carefully  built,  com- 
mence in  the  course  of  time  to  leak.  For  this  reason  tanks  of 
wood  lined  with  lead,  or  of  sheet-iron,  deserve  the  preference. 
Brick  tanks  lined  with  cement  may  also  be  used,  provided 
several  coats  of  thinly-fluid  asphalt  lacquer  be  applied  to  the 
cement  lining  to  prevent  the  latter  from  being  attacked  by  the 
acid  baths. 

Heating  the  zinc  baths  is  best  effected  by  steam  introduced 
through  a  hard  lead  (alloy  of  antimony  and  lead)  coil  oa  the 
bottom  of  the  tank. 

Execution  of  zincking. — Since  the  principal  object  of  electro- 
zincking  is  to  prevent  rusting,  embellishing  the  metallic  ob- 
jects being  only  in  very  rare  cases  effected,  the  mechanical 
30 


466  ELECTRO-DEPOSITION    OF    METALS. 

refinement  of  the  surface  by  grinding  is  as  a  rule  omitted,  a 
purely  metallic  surface  free  from  scale  being  produced  in  a 
cheaper  manner. 

This  is  done  by  pickling,  scratch-brushing,  scrubbing  with 
sand  in  a  drum,  or  by  the  sand-blast.  The  latter  deserves  the 
preference  for  large  quantities  of  small  articles,  as  well  as  for 
objects  with  not  too  large  surfaces.  For  freeing  large  surfaces 
of  sheet  from  scale,  the  use  of  the  sand-blast  is,  however,  too 
expensive  on  account  of  the  great  consumption  of  power,  and, 
besides,  takes  too  much  time. 

In  electro-zincking  particularly,  the  mode  of  operating  de- 
pends entirely  on  the  nature  and  form  of  the  objects,  and  it  is, 
therefore,  advisable  to  discuss  separately  the  various  manipu- 
lations required  for  certain  objects. 

bucking  sheet-iron.  When  the  sheets  have  been  freed  from 
grease  by  means  of  hot  alkaline  lyes  or  lime  paste,  they  are 
pickled  in  dilute  sulphuric  or  hydrochloric  acid,  and  the 
loosened  scale  is  removed  by  scouring  with  fire  brick  and 
sand.  The  use  of  a  pickle  of  hydrochloric  acid  2  parts,  sul- 
phuric acid  of  66°  Be.,  1  part,  and  water  17  parts  is  also  of 
advantage.  To  what  extent  the  electrolytic  method  of  pick- 
ling, previously  referred  to,  can  be  used  to  advantage  for  this 
purpose,  has  thus  far  not  been  practically  determined.  By 
the  use  of  a  sand-blast  the  cleanest  and  most  complete  results 
are  obtained,  but  the  expense  for  power  has  to  be  taken  into 
consideration. 

As  in  all  other  electro-plating  processes,  a  purely  metallic 
surface  free  from  scale  is  an  absolutely  necessary  condition  for 
a  well-adhering  deposit  of  zinc.  Portions  of  the  sheets  coated 
with  scales,  would  come  out  zincked,  but  in  the  further 
manipulation  of  the  sheets,  the  layer  of  zinc  becomes  de- 
tached, and  this  must  be  avoided. 

The  pickled  and  scoured  sheets,  generally  in  lengths  of  6 
feet  and  1  foot  wide,  are  secured  to  binding  screws  and  brought 
into  the  zinc  bath,  that  given  wilder  formula  I  being  especially 
suitable  for  the  purpose.  Heating  the  bath  to  between  104° 


DEPOSITION    OF    TIN,  ZINC,  LEAD    AND    IRON.  467 

and  113°  F.,  and  vigorous  agitation  by  blowing  in  air,  or  by 
means  of  a  mechanical  contrivance,  allows  of  working  with  a 
current-density  of  2J  amperes,  and,  if  necessary,  more,  at 
which  a  sufficiently  heavy  deposit  to  protect  the  objects  from 
rust  is  in  20  to  25  minutes  obtained. 

In  working  on  a  large  scale,  it  is  advisable  to  couple  the 
baths  in  series  and  to  zinc  in  each  bath  3  sheets,  each  2x1 
meters,  with  a  total  surface  of  12  square  meters  per  bath. 
Hence,  for  zincking  the  sheets  on  both  sides  and  working  with 
a  current-density  of  2.5  amperes  per  square  decimeter,  there 
will  be  required  four  baths  in  series,  each  with  12  square 
meters  of  surface,  a  dynamo  of  12  x  250  =  3000  amperes,  and 
the  electro-motive  force  should  be  12  volts,  2J  to  3  volts  be- 
ing required  per  bath.  With  such  a  plant  working  for  10 
hours,  340  to  360  sheets,  each  2x1  meters,  can  be  zincked  on 
both  sides  so  as  to  protect  them  from  rust,  and  by  working 
day  and  night,  820  to  850  sheets. 

When  zincking  is -finished,  the  sheets  are  rinsed  in  water, 
then  immersed  in  boiling  water  until  they  have  acquired  the 
temperature  of  the  latter,  and  finally  set  up  free,  or  hung  up 
to  dry.  The  hot  sheets  then  dry  in  a  few  minutes. 

The  zincked  sheets  show  a  pale-gray,  mat,  velvety  appear- 
ance, and  are  generally  used  in  this  state.  If  the  zinc  deposit 
is  to  be  lustrous,  the  sheets  are  scratch-brushed,  best  dry,  with 
steel  scratch-brushes. 

Zincking  of  pipes.  The  pipes  are  freed  from  scale  either  by 
means  of  the  sand'  blast  or  by  pickling  and  scouring.  To 
protect  the  screw  threads  from  the  pickle,  they  are  coated 
with  tallow  which,  however,  previous  to  zincking,  has  to  be 
removed  with  hot  soda  lye  or  rubbing  with  benzine,  and  care 
must  be  had  thoroughly  to  free  them  from  grease  with  lime 
paste. 

The  pipes,  best  four  or  six  pieces  one  above  the  other,  are 
placed  upon  a  frame  which  also  serves  for  conducting  the  cur- 
rent, and,  if  they  are  of  considerable  diameter,  it  is  advisable 
to  turn  them  90°  when  half  the  time  for  zincking  has  expired, 
in  order  to  obtain  a  uniform  deposit. 


468  ELECTRO-DEPOSITION    OF    METALS. 

While  in  zincking  straight  flat  sheets,  the  distance  of  the 
anodes  from  the  cathodes  need  only  be  1.96  to  2.35  inches, 
the  distance  of  the  zinc  anodes  from  the  pipes  should  be  the 
greater,  the  larger  the  diameter  of  the  latter  is.  Pipes  of  very 
large  diameter  are  best  suspended  alongside  each  other,  instead 
of  one  above  the  other,  a  row  of  anodes  of  zinc  sheet  suitably 
bent  being  arranged  between  every  two  pipes.  Frequent 
turning  of  the  pipes  is  required,  and  uniform  zincking  is  pro- 
moted by  heating  the  bath  and  by  vigorous  agitation.  The 
further  manipulation  of  the  zincked  pipes  is  similar  to  that 
given  for  sheets. 

Zincking  the  insides  of  the  pipes  is  a  more  difficult  opera- 
tion. To  commence  with,  it.  is  as  a  rule  a  difficult  task  to 
find  out  whether  pickling  and  scratch-brushing  has  been 
sufficiently  done  and  a  pure  metallic  surface  have  everywhere 
been  produced.  Special  directions  for  inside  zincking  depend 
partly  on  the  diameter,  and  it  can  only  be  said  in  general  that 
it  is  best  to  zinc  the  pipes  while  in  a  vertical  or  half-lying  posi- 
tion and  to  provide  for  a  constant  renewal  of  the  electrolyte  in 
the  interior. 

Zincking  of  wrought-iron  girders,  T-iron,  \J-iron,  {..'iron,  etc. 
The  cheapest  plan  of  freeing  the  objects  from  scale  is  by  pick- 
ling in  dilute  sulphuric  or  hydrochloric  acid  and  vigorous 
scrubbing  with  sand,  or  scratch-brushing.  The  use  of  a  trans- 
portable sand  blast  is  also  very  suitable,  but  this  method  is 
more  expensive  than  the  former. 

For  the  uniform  zincking  of  such  profiled  objects,  the  use  of 
flat  zinc  anodes  is  not  practicable,  far  more  zinc  being  deposited 
upon  the  edges  and  surfaces  next  to  the  anodes  than  upon  the 
depressed  portions.  Hence,  in  addition  to  heating  and  vig- 
orously agitating  the  bath,  recourse  must  be  had  to  profiled 
anodes  corresponding  to  the  shape  of  the  object  to  be  zincked, 
the  object  of  such  profiled  anodes  being  solely  to  bring  all  por- 
tions of  the  objects  at  as  nearly  an  equal  distance  as  possible 
from  the  anodes. 

The  profiled  anodes  may  be  made  by  bending  zinc  sheets 


DEPOSITION    OF    TIN,  ZINC,  LEAD    AND    IRON. 


469 


into  the  proper  shape,  or  what  is  better,  by  riveting  or  screw- 
ing square  cast-zinc  bars  to  the  zinc  sheets,  this  being  of  ad- 
vantage, for  instance,  in  zincking  girders.  Figs.  132  and  133 
show  the  arrangement  of  the  anodes,  and  require  no  further 
explanation. 

In  zincking  profiled  objects  it  is  of  advantage  to  add  to  the 
bath  prepared  according  to  formula  I,  0.8  oz.  of  dextrose  per 
quart,  the  bath  working  better  in  the  deeper  portions  with 


FIG.  132. 


FIG.  133. 


such  an  addition  than  without  it.  Of  still  greater  advantage 
is  the  pyridine-zinc  bath  according  to  Goldberg. 

Zincking  of  wire,  steel  tapes,  cords,  etc. — Under  this  heading 
will  chiefly  be  considered  iron  and  steel  wire  which  is  to  be 
protected  from  rust  by  a  deposit  of  zinc.  As  previously  men- 
tioned when  speaking  of  nickeling  wire,  the  latter  has  to  be 
uncoiled  and  passed  at  a  suitable  rate  of  speed  through  the 
pickling  solutions  and  the  zinc  bath. 

Bright-drawn  iron  and  steel  wire,  requiring  but  little  prepar- 
atory work,  is  most  suitable  for  zincking.  It  suffices  for  coils 
of  such  wire,  when  free  from  rust,  to  push  them  upon  a  shaft 
of  corresponding  diameter,  and  bring  the  whole  into  a  tank 
with  hot  soda  lye,  which  is  furnished  with  bearings  for  the 


470  ELECTRO-DEPOSITION    OF    METALS. 

shaft.  From  this  tank  the  wire,  freed  from  grease  by  the  hot 
lye,  passes  through  a  few  felt  rolls  or  cloth  cheeks  supplied 
with  thin  lime  paste,  an  additional  freeing  from  grease  being 
thus,  for  the  sake  of  greater  security,  effected.  The  wire  is 
then  brought  under  a  rose  for  the  removal  by  water  of  adher- 
ing lye  and  lime,  then  slides  over  a  metallic  roll  which  is  in 
contact  with  the  negative  pole  of  the  source  of  current,  and 
passes  into  the  zinc  bath.  In  the  latter  zinc  anodes  are 
arranged  below  and  above  the  lengths  of  wires  running  parallel 
to  each  other.  Such  zinc  baths  for  wire  zincking  are  from  20 
to  26  feet  long.  The  average  velocity  with  which  wire  0.039 
inch  in  diameter  passes  through  the  bath  is  about  20  feet  per 
minute.  For  wire  of  less  diameter  the  velocity  may  be  in- 
creased to  59  feet,  while  for  wire  of  greater  diameter  it  has  to 
be  correspondingly  decreased. 

When  the  wire  comes  from  the  bath  it  is  conducted  through 
a  tank  containing  boiling  water,  and  is  then  reeled  up.  The 
contrivances  for  reeling  up  the  wire  are  best  driven  by  an 
electro-motor  with  the  use  of  a  starting  resistance  for  regu- 
lating the  turns,  it  being  thus  possible  to  choose  and  change 
at  will  the  velocity  of  the  passage  of  the  wire  in  the  bath. 

Zincking  of  wires  produced  by  rolling  is  not  quite  so 
simple.  Such  wire,  which  is  readily  recognized  by  its  black 
appearance,  is  coated  with  a  scale,  which  adheres  very  firmly 
by  reason  of  the  rolling  process.  Previous  to  zincking,  such 
wire  has  to  be  carefully  freed  from  scale  in  order  to  obtain 
a  purely  metallic  surface.  This  may  be  accomplished  in 
various  ways,  the  method  selected  depending  on  the  nature 
and  properties  of  the  material  to  be  manipulated. 

Experiments  in  cleansing  such  wire  by  means  of  the  sand 
blast  did  not  yield  satisfactory  results,  the  process  being  too 
slow  notwithstanding  the  use  of  suitable  annular  blast-pipes. 
Hence  recourse  will  have  to  be  had  to  pickling  in  acids,  but 
many  kinds  of  wire  and  steel  tapes  stand  pickling  only  for  a 
very  short  time,  as  they  readily  become  brittle.  Wire  which 
does  not  show  this  drawback  is  pickled  until  the  scale  is  par- 


DEPOSITION    OF    TIN,  ZINC.   LEAD    AND    IRON.  471 

tially  dissolved,  or  at  least  very  much  loosened.  After  rinsing 
in  water,  it  is  immersed  in  boiling  water  so  that  it  will  dry 
rapidly  and  then,  for  the  removal  of  the  loosened  scale,  passed 
by  means  of  a  suitable  contrivance  through  the  scratch-brush- 
ing machine.  Wire  which  will  not  bear  pickling  at  all,  or 
only  for  a  very  short  time,  has  to  be  brightened  by  mechanical 
means,  either  by  the  drawing-plate,  or  by  conducting  it  over 
revolving,  hard  grindstones  or  emery  wheels  provided  with 
insertions  for  holding  it. 

Zincking  of  screws,  nuts,  rivets,  nails,  tacks,  etc.  Such  small 
objects  are  freed  from  grease  either  by  means  of  the  sand  blast 
or  in  tumbling  barrels  with  the  use  of  wet,  sharp  sand.  When 
the  latter  process  is  employed,  the  objects  have  of  course  to  be 
immediately  zincked  to  prevent  rusting. 

For  zincking  quantities  of  such  small  objects,  one  of  the 
mechanical  plating  contrivances  referred  to  under  "  Deposi- 
tions of  Nickel  "  is  very  suitable.  When  zincking  is  effected 
in  baskets  the  position  of  the  objects  has  to  be  frequently 
-changed  by  stirring  in  order  to  insure  a  uniform  deposit. 

The  bath  prepared  according  to  formula  II,  when  heated, 
is  very  well  adapted  for  zincking  small  objects  in  large  quan- 
tities. With  the  use  of  a  mechanical  plating  apparatus,  it  is 
possible  in  consequence  of  the  constant  agitation,  to  work  with 
high  current-densities  and  to  deposit  a  correspondingly  large 
quantity  of  zinc  in  a  comparatively  short  time. 

The  further  manipulation  of  the  zincked  small  objects  con- 
sists in  washing  them  in  baskets  and  drying  them  quickly  by 
immersion  in  boiling  water  and  shaking  with  heated  clean 
sawdust,  though  the  latter  operation  may  be  omitted. 

For  zincking  by  contact,  see  special  chapter  "  Depositions  by 
€ontact." 

Zinc  alloys. — The  production  of  the  principal  zinc  alloy, 
brass,  by  the  electric  method,  having  already  been  mentioned, 
-and  also  that  of  a  ziivc-nickel-copper  alloy  (German  silver),  it 
remains  to  give  an  alloy  of  zinc  with  tin,  or  of  zinc,  tin  and 
nickel,  which  can  be  produced  by  the  same  means. 


472  ELECTRO-DEPOSITION    OF    METALS. 

A  suitable  bath  for  depositing  this  alloy  consists  of :  Chlo- 
ride of  zinc  6|  drachms,  crystallized  stannous  chloride  & 
drachms,  pulverized  tartar  9  drachms,  pyrophosphate  of  soda 
2|  drachms,  water  1  quart.  Dissolve  the  salt  at  a  boiling 
heat,  and  filter  the  cold  solution,  when  it  is  ready  for  use.  For 
anodes,  cast  plates  of  equal  parts  of  tin  and  zinc  are  used. 

These  deposits  have  no  special  advantages,  but,  on  the  other 
hand,  a  deposit  containing  zinc  in  large  excess  has  the  same- 
effect  of  protecting  iron  from  rust  as  a  deposit  of  pure  zinc. 

By  preparing  a  bath  which  contains  as  conducting  salt 
sodium  citrate,  and  ammonium  chloride  and  the  chlorides  of 
the  metals  in  the  proportion  of  4  zinc  chloride  to  1  tin  chloride, 
a  deposit  is  obtained,  which  not  only  is  a  perfect  protection 
against  rust,  but  also  enters  far  better  into  depressions  than, 
pure  zinc.  By  adding  to  the  bath  a  small  quantity  of  chlo- 
ride of  mercury,  or  of  nickel,  alloys  of  zinc,  tin,  mercury,  or 
of  zinc,  tin  and  nickel  are  formed,  which  are  distinguished 
from  pure  zinc  deposits  by  a  finer  structure. 

2.  DEPOSITION  OF  LEAD  (Pb  =  207.10  parts  by  weight). 

The  properties  of  lead  only  interest  us  in  so  far  as  it  is  less 
attacked  by  most  mineral  acids  than  any  other  metal,  and 
against  the  action  of  such  agents.  For  decorative  purposes 
electro-deposits  of  lead  are  scarcely  used,  and  those  as  a  pro- 
tection against  chemical  influences  cannot  be  produced  of 
sufficient  thickness  for  that  purpose. 

Lead  baths. — I.  Dissolve,  by  continued  boiling,  caustic  pot- 
ash 1.75  ozs.  and  finely  pulverized  litharge  0.17  oz.  in  1  quart 
of  water. 

II.  According  to  Watt,  the  following  solution  is  used  : 
Acetate  of  lead  0.17  oz.,  acetic  acid  0.17  oz.,  water  1  quart. 

The  bath  prepared  according  to  formula  I  deserves  the 
preference. 

Lead  baths  require  anodes  of  sheet-lead  or  cast-lead  plates, 
a  weak  current  and,  in  order  to  produce  a  dense  deposit  of 
some  thickness,   the  objects  have  to  be  frequently  scratch- 


DEPOSITION    OF    TIN,  ZINC,  LEAD    AND    IRON. 

brushed.  Iron  is  best  previously  coppered.  Peroxide  of  lead 
is  separated  on  the  anodes,  and  they  have  to  be  frequently 
cleansed  with  a  scratch-brush.  The  formation  of  peroxide  of 
lead  on  the  anodes  is  utilized  for  the  production  of  the  so- 
called  Nobili's  rings  (electrochromy). 

Metallo-chromes  (Nobili's  rings,  iridescent  colors,  electro- 
chromy). The  reduction  of  peroxide  of  lead  upon  the  anodes 
or  upon  objects  suspended  as  anodes,  produces  superb  effects 
of  colors.  For  the  production  of  such  colors,  a  bath  is  pre- 
pared by  boiling  for  half  an  hour  3J  ozs.  of  caustic  potash, 
14  drachms  of  litharge,  and  1  quart  of  water.  The  operation 
is  as  follows :  Suspend  the  articles,  carefully  freed  from  grease 
and  pickled,  to  the  anode-rods,  and  with  a  weak  current  intro- 
duce in  the  lead  solution  a  thin  platinum  wire  connected  with- 
the  object-rod  by  flexible  copper  wire,  without,  however,  touch- 
ing the  article.  The  latter  will  successively  become  colored 
with  various  shades — yellow,  green,  red,  violet  and  blue.  By 
the  continued  action  of  the  current,  these  colors  pass  into  a 
discolored  brown,  which  also  appears  in  the  beginning  if  the 
current  be  too  strong,  or  if  the  platinum  wire  be  immersed  too 
deep.  Such  unsuccessful  coloration  has  to  be  removed  by 
rapidly  dipping  in  nitric  acid, 'and,  after  rinsing  in  water,, 
suspending  the  article  in  the  bath.  For  coloring  not  too  large 
surfaces,  a  medium-sized  Bunsen  cell  is,  as  a  rule,  sufficient,  if 
the  platinum  wire  be  immersed  about  f  inch. 

Colors  of  all  possible  beautiful  contrasts  may  be  obtained 
by  perpendicularly  placing  between  the  objects  to  be  colored 
and  the  platinum  wire  a  piece  of  stout  parchment  paper,  or 
providing  the  latter  with  many  holes  or  radial  segments. 

Another  process  of  producing  these  effects  of  colors  is  as 
follows :  Prepare  a  concentrated  solution  of  acetate  of  lead 
(sugar  of  lead),  and  after  filtering,  pour  it  into  a  shallow  porce- 
lain dish.  Then  immerse  a  plate  of  polished  steel  in  the 
solution,  and  allow  it  to  rest  upon  the  bottom  of  the  dish. 
Now  connect  a  small  sheet  of  disc  copper  with  the  wire  pro- 
ceeding from  the  zinc  element  of  a  constant  battery  of  two  or 


474  ELECTRO-DEPOSITION    OF    METALS. 

three  cells,  the  wire  connected  with  the  copper  element  being 
.placed  in  contact  with  the  steel  plate.  If  now  the  copper  disc 
be  brought  as  close  to  the  steel  plate  as  possible  without  touch- 
ing it,  in  a  few  moments  a  series  of  beautiful  prismatic  colora- 
tions will  appear  upon  the  steel  surface,  when  the  plate  should 
be  removed  and  rinsed  in  clean  water.  These  colorations  are 
films  of  lead  in  the  form  of  peroxide,  and  the  varied  hues  are 
due  to  the  difference  in  thickness  of  the  precipitated  peroxide 
of  lead,  the  light  being  reflected  through  them  from  the  pol- 
ished metallic  surface  beneath.  By  reflected  light  every  pris- 
matic color  is  visible,  and  by  transmitted  light  a  series  of 
prismatic  colors  complementary  to  the  first  colors  will  appear 
occupying  the  place  of  the  former  series.  The  colors  are  seen 
to  the  greatest  perfection  by  placing  the  plate  before  a  window 
with  the  back  to  the  light,  and  holding  a  piece  of  white  paper 
at  such  an  angle  as  to  be  reflected  upon  its  surface.  The 
colorations  are  not  of  a  fugitive  character,  but  will  bear  a 
considerable  amount  of  friction  without  being  removed.  In 
proof  of  the  lead  oxide  being  deposited  in  films  or  layers,  it 
may  be  stated  that  if  the  deposit  be  allowed  to  proceed  a  few 
seconds  beyond  the  time  when  its  greatest  beauties  are  exhib- 
ited, the  coloration  will  be  less  marked,  and  become  more  or 
less  red,  green  or  brown.  If  well  rubbed,  when  dry,  with  the 
finger  or  fleshy  part  of  the  hand,  a  rich  blue-colored  film  will 
be  laid  bare  by  the  removal  of  the  delicate  film  above  it. 

The  plan  recommended  by  Mr.  Gassiot  to  obtain  the  metallo- 
chromes  is  to  place  over  the  steel  plate  a  piece  of  cardboard  or 
parchment  paper  cut  into  some  regular  design,  and  over  this  a 
rim  of  wood,  the  copper  disc  being  placed  above  this.  Very 
beautiful  effects  are  obtained  when  a  piece  of  fine  copper  wire 
is  turned  up  in  the  form  of  a  ring,  star,  cross  or  other  pattern, 
and  connected  with  the  positive  electrode,  this  being  in  fact 
one  of  the  simplest  and  readiest  methods  of  obtaining  the 
•colorations  upon  the  polished  metal.  Metallochromy  is  ex- 
tensively employed  in  Nuremberg  to  ornament  metallic  toys. 
It  has  been  adopted  in  France  for  coloring  bells,  and  in 


DEPOSITION    OF    TIN,  ZINC,  LEAD    AND    IRON.  475 

Switzerland  for  coloring  the  hands  and  dials  of  watches.  In 
using  the  lead  solutions  to  produce  metallochromes,  it  must 
be  remembered  that  metallic  lead  becomes  deposited  upon  the 
•cathode,  consequently  the  solutions  in  time  become  ex- 
hausted, and  must  therefore  be  renewed  by  the  addition  of 
the  lead  salt. 

For  the  preparation  of  iridescent  sheets,  i.  e.,  nickeled  zinc 
sheet  coated  with  peroxide  of  lead,  a  sheet  of  lead  of  the  same 
size  as  the  sheet  to  be  made  iridescent  is  used  as  object,  and 
a  current  of  about  2£  volts  is  employed.  The  slime  formed 
in  the  bath  must  from  time  to  time  be  removed,  as  otherwise 
the  tones  of  color  will  not  turn  out  pure. 

4.  DEPOSITION  OF  IRON  (Fe  =55.85  parts  by  weight)  (STEELING). 

The  principal  practical  use  of  the  electro-deposition  of  iron 
is  to  coat  printing  plates  of  softer  metal  to  increase  their  wear- 
ing qualities.  We  are  indebted  to  Bottger  for  calling  attention 
to  the  employment  of  iron  deposits,  but  notwithstanding  the 
efforts  of  many  scientific  and  practical  men  to  improve  the 
process,  the  expectation  entirely  to  replace  copper  galvano- 
plasty  for  cliches  by  iron-galvanoplasty  has  not  been  fulfilled. 

Only  such  baths  as  are  suitable  for  steeling  will  here  be 
given.  Solutions  for  the  production  of  thick  iron  deposits, 
and  the  conditions  under  which  they  can  be  obtained,  will  be 
referred  to  later  on  under  "  Galvanoplasty  in  Steel." 

Iron  (steel)  baths.  I.  According  to  Varrentrapp:  Pure  green 
vitriol  4J  ozs.,  ammonium  chloride  3J  ozs.,  water  1  quart. 

Electro-motive  force  at  10  cm.  electrode-distance,  1.0  volt. 

Current-density,  0.2  ampere. 

Boil  the  water  for  \  hour  to  expel  all  air,  and,  after  cooling, 
add  the  green  vitriol  and  ammonium  chloride.  By  the  action 
of  the  air,  and  the  oxygen  appearing  on  the  anodes,  this  bath 
is  readily  decomposed,  insoluble  basic  sulphate  of  iron  being 
separated  as  a  delicate  powder,  which  has  to  be  frequently 
removed  from  the  fluid  by  filtering.  To  decrease  decomposi- 
tion, the  double  sulphate  of  iron  and  ammonium,  which  can 


476  ELECTRO-DEPOSITION    OF    METALS. 

be  more  readily  obtained  pure  and  free  from  oxide,  may  be 
used. 

II.  Ammonium  chloride  3J  ozs.,  water  1  quart. 
Electro-motive  force  at  10  cm.  electrode  distance,  1.0  volt. 
Current-density,  0.2  ampere. 

This  neutral  solution  of  ammonium  chloride  may  be  made 
into  an  iron  bath  by  hanging  in  it  iron  sheets  as  anodes,  sus- 
pending an  iron  or  copper  plate  as  cathode,  and  allowing  the 
current  to  circulate  until  a  regular  separation  of  iron  is  at- 
tained, which  is  generally  the  case  in  5  to  6  hours.  Although 
a  separation  of  hydrated  oxide  of  iron  also  takes  place  in  this 
bath,  it  does  so  in  a  less  degree  than  in  that  prepared  accord- 
ing to  formula  I.  For  the  production  of  not  too  heavy  a 
deposit  of  iron,  some  operators  claim  to  have  obtained  the 
best  results  with  this  bath. 

According  to  Bottger,  the  following  bath  serves  for  steeling  : 

Ila.  Potassium  ferrocyanide  fellow  prussiate  of  potash)  0.35 
oz.,  Rochelle  salt  0.7  oz.,  distilled  water  200  cubic  centimeters. 
To  this  solution  is  added  a  solution  of  1.69  drachms  of  persul- 
phate of  iron  in  50  cubic  centimeters  of  water,  whereby  a 
moderate  separation  of  Berlin  blue  takes  place.  Then  add, 
drop  by  drop,  whilst  stirring  constantly,  solution  of  caustic 
soda  until  the  blue  precipitate  has  disappeared.  The  clear, 
slightly  yellowish  solution  thus  obtained  can  be  used  directly 
for  steeling. 

A  heavy  and  very  hard  deposit  of  iron  is  obtained  in  a 
bath  of  the  following  composition. 

III.  Ammonio-ferrous  sulphate  ]J  ozs.,  crystallized  citric 
acid  0.88  oz.,  water  1   quart ;  sufficient  ammonia  for  neutral 
or  slightly  acid  reaction. 

E leer o-motive  force  at  10  cm.  electrode-distance,  2.0  volts. 

Current-density,  0.3  ampere. 

Management  of  iron  baths.  As  previously  mentioned,  the 
insoluble  precipitate  from  time  to  time  formed  in  the  bath 
has  to  be  removed  by  filtration.  This  precipitate  is,  however, 
very  delicate,  and  when  stirred  up  might  settle  upon  the 


DEPOSITION    OF    TIN,  ZINC,  LEAD    AND    IRON.  477 

objects  arid  prevent  the  adherence  of  the  deposit.  It  is,  there- 
fore, advisable  to  use  for  steel  baths,  tanks  of  much  greater 
-depth  than  corresponds  to  the  height  of  the  objects,  whereby 
the  stirring-up  of  the  sediment  in  suspending  the  objects  is 
best  avoided. 

With  the  use  of  steel  anodes  the  baths  may  become  readily 
acid.  This  can  be  avoided  by  suspending  a  few  small  linen 
bags  filled  with  carbonate  of  magnesia  in  the  bath.  On  the 
other  hand,  anodes  of  soft  iron  make  the  electrolyte  alkaline, 
and  when  such  anodes  are  employed,  the  reaction  of  the  bath 
must  from  time  to  time  be  tested  and  the  neutral  reaction  be 
restored  by  the  addition  of  very  dilute  sulphuric  acid,  or  better, 
citric  acid. 

Deposits  produced  in  an  iron  bath  which  has  become  alka- 
line show  slight  hardness,  form  very  rapidly  with  a  mat  ap- 
pearance and  have  a  tendency  to  peel  off. 

Execution  of  steeling. — The  cleansed  and  pickled  objects  are 
placed  in  the  baths  according  to  formulae  I  and  II,  with  a 
current  of  1.5  to  2  volts,  and  the  anodes  at  a  distance  of  4  to 
4|  inches,  after  which  the  current  is  reduced  to  1  volt.  To 
produce  iron  deposits  of  any  kind  of  thickness,  the  escape  of 
the  hydrogen  bubbles  which  settle  on  the  objects  must  be  pro- 
moted by  frequent  blows  with  the  finger  upon  the  object-rod. 
When  steeling  is  finished,  the  articles  are  thoroughly  rinsed, 
then  plunged  into  very  hot  water,  and,  after  drying  in  sawdust, 
placed  for  several  hours  in  a  drying  chamber  heated  to  about 
212°  F.,  to  expel  all  moisture  from  the  pores. 

Steeling  of  printing  plates  has  the  advantage  over  nickeling, 
that  when  the  plates  are  worn  they  can  be  rapidly  freed  from 
the  deposit  by  dilute  sulphuric  acid  or  very  dilute  nitric  acid, 
and  resteeled.  It  has  been  ascertained  by  experiments  that 
the  capability  of  resistance  of  steeled  plates  is  less  than  that  of 
nickeled  plates,  200,000  impressions  having  been  made  with 
the  latter  without  any  perceptible  wear. 

For  steeling  printing  plates  a  bath  prepared  according  to 
formula  II  or  III  is  very  suitable. 


CHAPTER  XII. 

DEPOSITION    OF    ANTIMONY,    ARSENIC,    ALUMINIUM. 
1.  DEPOSITION  OF  ANTIMONY  (Sb  — 120.2  PARTS  BY  WEIGHT). 

Properties  of  antimony. — Electro-deposited  antimony  pos- 
sesses a  gray  luster,  while  native,  fused  antimony  shows  a 
silver-white  color.  Antimony  is  hard,  very  brittle,  and  may 
easily  be  reduced  to  powder  in  a  mortar.  It  melts  at  842°  F., 
and  at  a  strong  red  heat  takes  fire  and  burns  with  a  white 
flame,  forming  the  trioxide.  Its  specific  gravity  is  6.8.  It  is 
permanent  in  the  air  at  ordinary  temperatures.  Cold,  dilute, 
or  concentrated  sulphuric  acid  has  no  effect  upon  antimony, 
but  the  hot  concentrated  acid  forms  sulphide  of  antimony. 
By  nitric  acid  the  metal  is  more  or  less  energetically  oxidized, 
according  to  the  strength  and  temperature  of  the  acid. 

Antimony  baths. — Electro-depositions  of  antimony  are  but 
seldom  made  use  of  in  the  industries>  though  they  are  very 
suitable  for  decorative  contrasts.  This  is  no  doubt  due  to  the 
fact  that  a  thoroughly  reliable  bath  yielding  deposits  without 
the  appearance  of  drawbacks  during  the  operation  is  thus  far 
not  known. 

For  the  special  study  of  electro-depositions  of  antimony  we 
are  indebted  to  Bottger  and  Gore,  the  latter  having  discovered 
the  explosive  power  of  deposits  of  antimony  deposited  from  a 
solution  containing  chloride  or  hydrochloric  acid. 

According  to  Gore,  a  bath  consisting  of  tartar  emetic  3  ozs.r 
tartaric  acid  3  ozs.,  hydrochloric  acid  4J  ozs.,  and  water,  1 
quart,  yields  a  gray,  crystalline  deposit  of  antimony.  This 
bath  requires  a  current  of  about  3  volts.  The  deposit  possesses 
the  property  of  exploding  when  scratched  or  struck  with  a 
hard  object.  The  explosion  is  attended  by  a  cloud  of  white 

(478) 


DEPOSITION    OF    ANTIMONY,    ARSENIC,    ALUMINIUM.          479" 

vapor,  and  sometimes  by  a  flash  of  light,  considerable  heat 
being  always  evolved.  This  explosibility  is  due  to  a  content 
of  antimony  chloride.  Bottger  found  3  to  5  per  cent,  of  chlo- 
ride of  antimony  in  the  deposit,  and  Gore  6  per  cent.  A 
similar  explosive  deposit  is  obtained  by  electrolyzing  a  simple 
solution  of  chloride  of  antimony  in  hydrochloric  acid  (liquid 
butter  of  antimony,  liquor  stibii  chlorati)  with  the  current. 

A  lustrous,  non-explosive  deposit  of  antimony  is  obtained 
by  boiling  4.4  ozs.  of  carbonate  of  potash,  2.11  ozs.  of  pulver- 
ized antimony  sulphide,  and  1  quart  of  water  for  1  hour,  re- 
placing the  water  lost  by  evaporation,  and  filtering.  Use  the 
bath  boiling  hot,  employing  cast  antimony  plates  or  platinum 
sheets  as  anodes. 

An  antimony  bath  which  yields  good  results  is  composed  as 
follows : 

Schlippe's  salt  1}  ozs.,  water  1  quart.  Dissolve  the  salt  in 
the  water.  Electro-motive  force  required,  4  volts.  An  un- 
pleasant feature  of  this  bath  is  that  during  electrolyzing  sul- 
phuretted hydrogen  escapes,  which  limits  its  application. 

2.  DEPOSITION  OP  ARSENIC  (As  74.96  PARTS  BY  WEIGHT). 

Properties  of  arsenic. — Arsenic  has  a  gray-white  color,  a 
strong  metallic  luster,  is  very  brittle,  and  evaporates  at  a  red 
heat.  In  dry  air  arsenic  retains  its  luster,  but  soon  turns  dark 
in  moist  air.  It  is  scarcely  attacked  by  dilute  hydrochloric 
and  sulphuric  acids,  while  concentrated  sulphuric  acid,  as  well 
as  nitric  acid,  oxidizes  it  to  arsenious  acid.  If  caustic  alkalies 
are  fused  together  with  arsenic,  a  portion  of  the  latter  is  con- 
verted into  alkaline  arsenate. 

Arsenic  baths. — Arsenic  solutions  are  extensively  used  in  the 
plating  room  for  decorative  purposes  in  order  to  produce  blue- 
gray  to  black  tones  of  a  certain  warmth,  which  are  very  effec- 
tive in  combination  with  bright  copper,  brass,  etc. 

For  coloring  all  kinds  of  metals  blue-gray  the  following 
solutions  are  very  suitable  : 

I.  Pulverized  white  arsenic  If  ozs.,  crystallized  pyrophos- 


480  ELECTRO-DEPOSITION    OF    METALS. 

phate  of  soda  0.7  oz.,  98  per  cent,  potassium  cyanide  1  j  ozs., 
water  1  quart. 

Dissolve  the  pyrophosphate  of  soda,  and  the  potassium 
cyanide  in  the  cold  water,  and  after  adding,  whilst  stirring, 
the  arsenic  acid,  heat  until  the  latter  is  dissolved.  In  heat- 
ing, fumes  containing  prussic  acid  escape,  the  inhalation  of 
which  must  be  carefully  avoided.  The  bath  is  used  warm, 
and  requires  a  vigorous  current  of  at  least  4  volts,  so  that,  at 
the  least,  3  Bunsen  cells  have  to  be  coupled  for  electro- motive 
force.  After  suspending  the  objects  they  are  first  colored 
'black-blue,  the  color  passing  with  the  increasing  thickness  of 
the  deposit  into  pale  blue,  and  finally  into  the  true  arsenic 
gray.  Platinum  sheets  or  carbon  plates  are  to  be  used  as 
anodes. 

In  place  of  the  bath  prepared  according  to  formula  I,  a 
solution  of  the  following  composition  may  be  used  : 

II.  Sodium  arsenate  1}  ozs.,  98  per  cent,  potassium  cyanide 
'0.8  oz.,  water  1  quart.  Boil  the  solution  for  half  an  hour,  then 
filter  and  use  it  at  a  temperature  of  at  least  167°  to  176°  F., 
with  a  strong  current.  It  yields  a  good  deposit. 

Large  baths,  to  be  used  cold,  must  be  more  concentrated, 
and  require  a  stronger  current  than  hot  baths. 

When  the  baths  begin  to  work  irregularly  and  sluggishly, 
they  have  to  be  replaced  by  fresh  solutions. 

The  same  rules  as  for  other  electro-plating  processes  are  to 
toe  observed  in  depositing  arsenic  and  antimony. 

However,  attention  may  here  be  called  to  one  feature 
which  is  frequently  the  cause  of  defective  deposits.  When, 
for  instance,  mountings  of  zinc,  such  as  are  used  for  book 
covers,  jewel  boxes,  etc.,  are  to  be  provided  with  a  deposit  of 
•copper  and  arsenic,  and  hence  are  to  show  two  colors,  it  is 
necessary  to  first  copper  them.  After  polishing  and  cleaning 
the  coppered  mountings,  the  places  which  are  not  to  receive 
the  blue-gray  deposit  of  arsenic  are  coated  with  stopping-off 
varnish.  When  articles  thus  treated,  after  being  again  freed 
from  grease  and  pickled,  are  brought  into  the  arsenic  bath, 


DEPOSITION    OF    ANTIMONY,    ARSENIC,    ALUMINIUM.          481 

they  frequently  show  ugly  stains  the  size  of  a  pin-head. 
This  feature,  however,  does  not  appear  when  the  articles  be- 
fore being  brought  into  the  bath  are  drawn  through  water 
acidulated  with  a  small  quantity  of  nitric  acid  (about  J  oz. 
of  nitric  acid  to  1  quart  of  water),  and  thoroughly  rinsed  in 
clean  water. 

Mr.  Emmanuel  Blassett,  Jr.,*  gives  the  following  solutions 
for  coloring  articles  black  : 

III.  White  arsenic  1  lb.,  potassium  cyanide  2  Ibs.,  water  6 
gallons,  ammonium  carbonate  10  ozs. 

Dissolve  the  white  arsenic  and  potassium  cyanide  in  5  gal- 
lons of  water,  and  the  ammonium  carbonate  separately  in  1 
gallon  of  water,  and  mix  the  two  solutions.  This  solution  is 
worked  cold.  Steel  or  brass  anodes  may  be  used  and  a  cur- 
rent with  the  tension  of  1  volt  is  sufficient.  Without  the 
ammonium  carbonate  the  deposit  is  not  so  black  and  is  in- 
clined to  be  steel-gray  in  color.  It  is  a  difficult  operation  to 
•color  small  light  pieces  in  this  bath,  possibly  due  to  the  poor 
conductivity  of  arsenic  solutions.  On  very  light  articles  the 
bath  gives  an  iridescent  color,  or  blue-black  at  the  most. 
For  this  reason  if  a  good  black  color  is  desired,  the  following 
dip  should  be  used  for  small  articles :  White  arsenic  2  ozs., 
potassium  cyanide  5  ozs.,  water  1  gallon. 

This  dip  is  used  hot  and  without  the  current.  The  solution 
is  made  up  in  an  enamel  or  agate  ware  vessel,  and  brought  to 
a  boiling  point  by  means  of  a  gas  stove.  Work  to  be  colored 
is  fastened  to  wires  or  immersed  in  the  solution  by  means  of 
a  plating  or  dip  basket.  Some  platers  make  up  a  new  dip 
every  day  or  two,  but  by  careful  management,  such  as  re- 
placing the  water  lost  by  evaporation  and  making  small  addi- 
tions of  arsenic  and  cyanide,  the  dip  may  be  made  to  last  a 
long  time. 

Another  arsenic  bath  is  made  up  as  follows : 

*  Metal  Industry,  March,  1913. 


482  ELECTRO-DEPOSITION    OF    METALS. 

IV.  White  arsenic  3  Ibs.,  potassium  cyanide  4  ozs.,  com- 
mercial caustic  soda  1J  Ibs.,  water  5  gallons. 

The  ingredients  are  boiled  together.     Soft  steel  or  brass 
anodes  are  used,  and  a  current  of  about  1  volt  is  required. 
A  favorite  bath  with  some  platers  is  composed  of: 

V.  White  arsenic  2  Ibs.,  copper  carbonate  4  ozs.,  potassium 
cyanide  2J  Ibs.,  water  5  gallons. 

In  addition  to  the  solutions  described,  which  are  all  alka- 
line, there  are  several  acid  arsenic  baths  which  are  frequently 
employed.  The  most  simple  is  composed  as  follows  : 

VI.  Muriatic  acid  5  gallons,  white  arsenic  2  Ibs. 

Carbon  anodes  are  often  used  in  operating  this  solution,  and 
for  that  reason  it  is  often  spoken  of  as  the  "  carbon  solution. " 
Acid  solutions  are  indispensable  on  work  where  a  portion  of 
the  surface  is  stopped  off  with  an  asphalt  paint  or  varnish. 
Strong  alkaline  solutions  ordinarily  will  remove  paint  or  var- 
nish and  spoil  the  finish,  unless  unusual  care  is  exercised. 

A  well-known  acid  bath  is  composed  as  follows : 

VII.  Muriatic   acid    1    gallon,   iron    filings   4   ozs.,   white 
arsenic  4  ozs. 

This  formula  is  very  suitable  for  producing  an  oxidized 
brass  effect.  The  coating  is  a  little  heavier,  as  iron  is  de- 
posited simultaneously  with  the  arsenic.  The  deposit  is  soft, 
and  may  be  easily  relieved  for  a  cut  through  finish.  In  all 
acid  baths  it  is  best  to  use  either  carbon  or  brass  anodes.  If 
iron  or  steel  anodes  are  used,  they  are  attacked  by  the  acid, 
producing  a  very  concentrated  solution.  Under  such  condi- 
tions particles  of  undissolved  iron  may  interfere  with  the 
operation. 

Some  platers  prefer  to  use  iron  sulphate  instead  of  iron 
filings  and  make  up  their  solution  as  follows : 

VII.  Muriatic  acid  5  gallons,  white  arsenic  1  lb.,  iron  sul- 
phate 1  lb. 

Electro-depositions  of  chromium,  tungsten,  cadmium  and) 
bismuth  have  thus  far  not  become  of  any  practical  import- 
ance, and  their  discussion  may,  therefore,  with  good  reason,. 


DEPOSITION    OF    ANTIMONY,    ARSENIC,    ALUMINIUM.          483 

be  omitted.     As  regards  silver-cadmium  deposits  the  reader  is 
referred  to  Areas-silvering  under  "Deposition  of  Silver." 

3.  DEPOSITION  OF  ALUMINIUM  (Al  =  27.1  PARTS  BY  WEIGHT). 

There  is  actually  no  reason  or  authority  for  the  heading  of 
this  section,  but  it  has  been  introduced  because  inquiries  are 
frequently  received  as  to  whether  baths  for  the  deposition  of 
aluminium  can  be  furnished. 

A  number  of  receipts  for  the  preparation  of  aluminium 
baths  have  been  published,  but  in  testing  them  nothing  fur- 
ther could  be  obtained  than  the  confirmation  of  the  fact  that 
the  deposition  of  aluminium  from  aqueous  solutions  of  its 
salts  by  the  current  upon  the  cathode  has  thus  far  not  been 
feasible. 

Reports  have  from  time  to  time  appeared  in  newspapers  of 
the  iron  construction  of  tall  buildings  having  been  provided 
with  a  heavy  deposit  of  aluminium,  and  even  the  processes 
used  have  been  fully  described.  It  is  to  be  regretted  that 
such  elaborate  reports  are  even  admitted  into  scientific  jour- 
nals, though  the  separation  of  romance  from  truth  could  be 
readily  accomplished  by  a  conscientious  examination.  Un- 
scrupulous dealers  offer  their  customers  aluminium  baths, 
charging  a  high  price  for  them,  and  on  testing  a  deposit  pro- 
duced with  such  baths,  it  has  frequently  been  found  to  consist 
solely  of  tin.  Others,  who  actually  had  faith  in  the  value  of 
their  invention  have  submitted  for  examination  objects  plated 
with  aluminium  by  their  processes.  On  testing  such  deposits 
it  was  found  that  in  one  case,  it  consisted  of  a  thin  deposit  of 
zinc,  the  origin  of  which  was  due  to  zinckiferous  aluminium 
salts,  and  in  other  cases,  of  a  deposit  of  iron  due  to  the  same 
cause. 

The  concurrence  of  the  above-mentioned  influences  and  the 
recent  rapid  development  of  the  aluminium  industry  explains 
the  demand  for  aluminium  baths  by  many  electro-platers. 
However,  without  entering  into  scientific  reasons,  which 
would  not  be  within  the  scope  of  this  work,  it  can  here  only 


484  ELECTRO-DEPOSITION    OF    METALS. 

be  repeated  that  the  reduction  of  metallic  aluminium  from  its 
solutions  will  very  likely  remain  an  empty  dream. 

4.  DEPOSITION  UPON  ALUMINIUM. 

The  electro-deposition  of  other  metals  upon  aluminium  pre- 
sents many  difficulties  which  are  chiefly  due  to  the  behavior 
of  this  metal  towards  the  plating  baths.  The  deposits  to  be 
sure  are  formed,  but  they  possess  no  adherence,  and  especially 
baths  containing  potassium  cyanide  yield  the  worst  results  in 
consequence  of  the  effect  of  alkaline  solutions  upon  the  basis- 
metal.  Since  the  production  of  aluminium  has  so  largely 
increased,  and  a  great  number  of  articles  of  luxury  and  for 
practical  use  are  now  made  of  this  metal,  the  need  of  decora- 
ting such  articles  by  electro-plating  or  covering  them  entirely 
with  other  metals  has  been  felt,  since  the  color  of  aluminium 
is  by  no  means  a  sympathetic  one.  Look  into  a  show  window 
where  aluminium  articles  are  exposed — nothing  but  gray  in 
gray.  Offended,  the  eye  of  the  observer  turns  away,  and 
seeks  a  more  agreeable  resting-place. 

Aluminium  behaves  so  differently  from  other  metals  towards 
the  cleansing  agents  generally  used,  that  different  methods 
from  those  previously  described  have  to  be  employed  in  pre- 
paring it  for  plating.  Nitric  acid  has  almost  no  effect  on 
aluminium,  and  pickle  just  a  little  ;  but,  on  the  other  hand, 
the  metal  is  attacked  by  concentrated  hydrochloric  acid, 
dilute  hydrofluoric  acid,  and  especially  by  alkaline  lyes. 
Hence,  if  polished  articles  of  aluminium  are  to  be  prepared 
for  plating,  alkaline  lyes  will  have  to  be  avoided  in  freeing 
them  from  grease,  it  being  best  to  use  only  benzine  for  the 
purpose.  Unpolished  articles  may  without  hesitation  be  freed 
from  grease  with  caustic  potash  or  soda  lye,  and,  for  the  pro- 
duction of  a  dead  white  surface,  be  for  a  short  time  pickled  in 
dilute  hydrofluoric  acid,  and  then  thoroughly  rinsed  in  run- 
ning water. 

For  producing  an  electro-deposit  upon  aluminium  it  has 
been  considered  advisable  to  first  copper  the  metal,  and  the 


DEPOSITION    OF    ANTIMONY,    ARSENIC,    ALUMINIUM.          485 

Aluminium  Gesellschaft  of  Neuhausen  recommends  for  this 
purpose  a  solution  of  nitrate  of  copper.  But  the  adherence  of 
the  copper  proved  also  insufficient,  because  in  the  subsequent 
silvering,  nickeling,  etc.,  the  deposit  raised  up. 

The  copper  bath  recommended  by  Delval,  consisting  of 
sodium  pryophosphate  3  ozs.,  copper  sulphate  (blue  vitriol) 
f  oz.,  sodium  bisulphite  j-  oz.,  water  1  quart,  also  proved 
unreliable. 

According  to  another  patented  process,  plating  of  aluminium 
is  claimed  to  be  effected  successfully,  and  without  defect,  by 
lightly  coating  the  metal  with  silver  amalgam  by  boiling  in  a 
silver  bath  compounded  with  potassium-mercury  cyanide. 
However,  this  treatment  did  not  always  yield  reliable  results.. 

According  to  Villon,  articles  of  aluminium  are  to  be  im- 
mersed for  one  hour  in  a  bath  consisting  of  glycerin  5J  ozs.r 
zinc  cyanide  0.88  oz.,  zinc  iodide  0.88  oz.,  and  then  heated  to 
a  red  heat.  When  cold,  they  are  washed  with  a  hard  brush 
and  water,  and  brought  into  the  gold  or  silver  bath.  The  suc- 
cess of  this  process  seems  also  questionable. 

The  best  and  most  reliable  process  is  without  doubt  the  one 
patented,  in  1893,  by  Prof.  Nees.  It  consists  in  first  immers- 
ing the  aluminium  articles  previously  freed  from  grease  in  caus- 
tic soda  lye  until  the  action  of  the  lye  upon  the  metal  is  recog- 
nized by  gas  bubbles  rising  to  the  surface.  The  articles  with- 
out being  previously  rinsed  are  then  for  a  few  minutes  immersed 
in  a  solution  of  77  troy  grains  of  chloride  of  mercury,  rinsed, 
again  brought  into  the  caustic  soda  lye,  and  then,  without 
rinsing,  suspended  in  the  silver  bath.  The  deposit  of  silver 
thus  obtained  adheres  very  firmly,  and  can  be  scratch-brushed, 
and  polished  with  the  steel  without  raising  up.  It  can  also 
be  directly  gilded,  brassed,  or,  after  previous  coppering  in  the 
potassium  cyanide  copper  bath,  provided  with  a  heavy  deposit 
of  nickel  and  polished  upon  polishing  wheels. 

Burgess  and  Hambuechen  *  found  it  best  to  first  zinc  the 

*  Electro-chemical  Industry,  1904,  No.  3. 


486  ELECTRO-DEPOSITION    OF    METALS. 

aluminium  in  an  acid  zinc  bath  containing  1  per  cent,  fluoric 
acid  ;  the  fluoric  acid  acts  as  a  solvent  upon  the  film  of  oxide 
formed  so  that  the  deposit  is  effected  upon  a  pure  metallic 
surface.  According  to  these  authors,  the  aluminium  article  is 
to  be  immersed  in  dilute  fluoric  acid  until  its  surface  appears 
slightly  rough  and  attacked.  It  is  then  to  be  rinsed  in  water, 
and  for  a  few  seconds  immersed  in  a  bath  of  sulphuric  acid 
100  parts  and  nitric  acid  75  parts.  It  is  then  again  thoroughly 
rinsed  in  water,  next  brought  into  a  zinc  bath  of  15°  Be.,  con- 
sisting of  zinc  sulphate  and  aluminium  sulphate,  and  acidu- 
lated with  1  per  cent,  of  fluoric  acid  or  the  equivalent  quan- 
tity of  potassium  fluoride,  and  zincked  for  15  to  20  minutes. 
For  subsequent  silvering  or  gilding  the  zinc  deposit  is  first 
coppered  in  the  potassium  cyanide  copper  bath. 

According  to  Gottig,  a  thin,  firmly-adhering  deposit  of  cop- 
per is  first  to  be  produced  upon  the  aluminium  by  triturating 
blue  vitriol  solution  with  tin-powder  and  whiting;  or  a  tin 
deposit  is  to  be  produced  by  applying  stannous  chloride-ammo- 
nium chloride  solution  by  means  of  a  soft  brass  brush. 

The  Mannesmann  Pipe  Works,  Germany,  produce  durable 
electro-deposits  by  brushing  the  aluminium  with  solutions  of 
sulphide  of  gold  and  sulphide  of  silver  in  balsam  of  sulphur  * 
and  volatile  oils,  and  burning  in  the  metals  in  a  muffle,  under 
exclusion  of  the  air,  at  840°  to  930°  F.  Thin  layers  of  metal 
which  are  reduced  adhere  firmly  to  the  aluminium,  and  are 
then  provided  with  an  electro-deposit  desired.  According  to 
a  process  patented  by  the  same  corporation,  the  articles  are 
provided  with  a  firmly  adhering  (?)  fikn  of  zinc  by  immersing 
them  in  boiling  solution  of  zinc  dust  in  caustic  soda,  and  are 
then  electro-plated. 

However,  in  view  of  the  fact  that  all  the  methods  mentioned 
above  partly  yield  uncertain  results,  it  has  recently  been  pro- 
posed first  to  provide  the  aluminium  in  readily-fusible  metallic 
salts  (cupric  chloride,  tin  salt)  with  a  coat  of  these  metals,  and 
then  treat  it  further  in  aqueous  electrolytes. 

*  Solution  of  sulphur  in  linseed  oil. 


CHAPTER  XIII. 

DEPOSITION  BY  CONTACT,  BY  BOILING,  AND  BY  FRICTION. 

IF  a  sheet  of  metal,  for  instance,  copper,  be  brought  into  a 
solution  which  contains  the  cations  of  a  metal  of  slighter 
-solution-tension  (p.  61),  for  example,  a  solution  of  potassium- 
silver  cyanide  in  water  with  an  excess  of  potassium  cyanide, 
which  has  been  heated  to  about  158°  F.,  the  following  process 
takes  place  :  By  the  osmotic  pressure  (p.  49)  the  metal-ions,  in 
this  case  silver-ions,  are  reduced  upon  the  copper  sheet,  the 
osmotic  pressure  of  the  solution  being  thereby  decreased.  In 
•consequence  of  this  decrease  in  the  osmotic  pressure,  copper- 
ions  can  be  forced  into  the  solution  by  the  solution-tension, 
while  additional  silver-ions  are  brought  to  separate  upon  the 
•copper  sheet.  Hence,  during  the  formation  of  the  deposit,  a 
solution  of  the  metal  to  be  coated  in  the  case  in  question,  cop- 
per, takes  place  at  the  same  time,  this  process  coming  to  a 
standstill  when  the  copper  sheet  has  been  covered  with  a* 
coherent  coat  of  silver,  which  prevents  further  solution  of 
•copper  in  the  electrolyte. 

The  process  may  also  be  explained  in  a  different  way, 
namely,  that  by  the  immersion  in  the  silver  solution  the 
•copper  is  negatively  charged,  positive  silver-ions  being  by 
reason  of  electrostatic  attraction  attracted  and  reduced  on  the 
-copper. 

The  deposits  produced  in  this  manner  are  generally  known 
-as  deposits  by  immersion,  or  when  the  electrolyte  is  highly 
•heated,  by  boiling. 

The  same  process  takes  place  when  metallic  objects  are 
plated  by  applying  by  means  of  a  brush  or  by  friction  an 

(487) 


488  ELECTRO-DEPOSITION    OF    METALS. 

electrolyte  which   contains   a   metal   with    slighter   solution- 
tension  than  possessed  by  the  rnetal  of  an  object  to  be  coated. 

Since  the  more  electro-positive  metals  of  the  old  series  of 
electro-motive  force  possess  a  greater  solution-tension  than 
the  electro-negative  metals,  it  may  be  briefly  stated,  that 
electro-positive  metals  when  immersed  in  suitable  solutions  of 
electro-negative  metals  reduce  the  latter,  and,  under  certain 
conditions,  become  coated  with  them  so  that  a  coherent  de- 
posit is  formed. 

From  the  process  above  described,  according  to  which  re- 
duction only  takes  place  till  the  electro-positive  metal  has  been 
provided  with  a  coherent  coating  of  the  electro-negative  metal, 
it  is  plain  that  such  deposits  can  be  only  very  thin  and  can- 
not be  increased  by  continued  action  of  the  electrolyte,  except 
recourse  be  had  to  other  means. 

The  process,  however,  is  a  different  one  when  a  deposit  is  to- 
be  produced  by  the  contact  of  one  metal  with  another  in  an 
electrolyte.  If  a  copper  sheet  dipping  in  a  potassium  cyanide 
solution  of  potassium-silver  cyanide  be  touched  with  an  electro- 
positive rnetal,  for  instance,  a  zinc  rod  or  a  zinc  sheet,  the 
latter  dipping  also  in  the  electrolyte,  an  electric  current  is 
generated  which  reduces  silver-ions  on  the  copper-sheet,  while 
o'n  the  zinc  sheet  zinc-ions  are  forced  into  solution.  However, 
even  when  the  copper  sheet  has  been  covered  with  a  coherent 
deposit  of  silver,  the  reduction  of  the  latter  goes  on  in  so  far 
as  the  silver  which  is  also  reduced  upon  the  zinc,  and  which 
interrupts  contact  with  the  electrolyte,  as  well  as  prevents 
further  migration  of  zinc-ions  into  the  solution,  is  only  from 
time  to  time  removed. 

The  contact  processes  can,  however,  be  applied  only  to  a 
limited  extent.  On  the  one  hand,  the  formation  of  uniformly 
heavy  deposits  upon  the  metallic  objects  is  excluded,  because 
by  reason  of  the  greater  current-densities  appearing  at  the 
point  of  contact  with  the  contact  metal,  a  heavier  reduction  of 
metal  takes  place  there  than  on  the  portions  further  removed 
from  the  point  of  contact,  except  the  latter  be  freq  uently 


BY    CONTACT,    BY    BOILING,    AND    BY    FRICTION.  489' 

changed.  On  the  other  hand,  the  constant  increase  of  dis- 
solved contact-metal  in  the  electrolyte  constitutes  a  drawback, 
and  is  the  cause  of  the  electrolytes,  as  a  rule,  giving  out  long 
before  their  content  of  metal  is  exhausted.  Finally,  the 
reduction  of  metal  upon  the  contact-metal  is  not  a  desirable 
feature. 

As  contact-metals,  zinc,  cadmium  and  aluminium  are  chiefly. 
used.  In  many  cases,  aluminium  being  a  highly  positive 
metal,  considerably  surpasses  in  its  effect  the  first-mentioned. 
metals,  and  possesses  the  advantage  of  not  bringing  into  the 
electrolyte,  metals  reducible  by  the  current.  Furthermore,. 
the  quantities  of  metal  deposited  upon  the  aluminium  can  be 
dissolved  with  nitric  acid  without  materially  attacking  the 
contact-metal.  Darlay  has  recommended  magnesium  as  a 
contact-metal  (German  patent  127,464).  It  presents,  however, 
no  advantage,  on  the  one  hand,  on  account  of  its  high  price 
and,  on  the  other,  by  reason  of  the  deficient  results  in  connec- 
tion with  the  baths  of  the  above-mentioned  patent. 

The  electrolytes  serving  for  depositions  by  contact  must. 
possess  definite  properties  if  they  are  to  yield  good  results. 

Since  the  currents  generated  by  contact  are  weak,  the  elec- 
trolyte should  possess  good  conductivity,  so  that  the  reduction. 
of  metal  does  not  take  place  too  slowly,  and   it  must  attack  — 
chemically  dissolve  —  the  contact-metal,  as  a  current  can  only 
be  generated  if  such  be  the  case.     Let  us  consider,  for  instance, 
a  well-known  gold  bath  for  hot  gilding  by  contact,  which  con- 
tains in  1  quart  of  water  77  grains  of  crystallized  sodium  phos- 
phate, 46J  grains  of  caustic  potash,  15J  grains  of  neutral  chlo- 
ride of  gold,  and  0.56  oz.  of  98  per  cent,  potassium  cyanide. 
It  will  be  found  that  only  a  slight  portion  of  the  potassium 
cyanide  is  consumed  for  the  conversion  of  the  chloride  of  gold 
potassium-gold  cyanide,  the  greater  portion  of  it  serving 


^ 

to  increase  the  conductivity  of  the  electrolyte.  The  caustic 
potash,  together  with  the  sodium  phosphate,  effects  the  alka- 
linity of  the  bath  which  is  required  for  attacking  and  dissolv- 
ing the  contact-metal,  whether  it  be  zinc,  cadmium,  aluminium. 


490  ELECTRO-DEPOSITION    OF    METALS. 

or  magnesium.  The  effect  of  the  alkaline  phosphate  as  such 
is  claimed  to  be  that  the  deposit  of  metal  which  results  not 
only  upon  the  objects  in  contact  with  the  contact-metal,  but 
also  upon  the  latter  itself,  does  not  firmly  combine  with  it, 
but  can  be  readily  removed  by  scratch-brushing. 

For  increasing  the  conductivity  of  electrolytes  containing 
potassium  cyanide,  a  greater  or  smaller  excess  of  the  latter  is 
used  either  by  itself  or  in  combination  with  chlorides,  for  in- 
stance, ammonium  chloride  or  sodium  chloride,  nearly  all 
•known  baths  for  contact-deposition  containing  these  salts  in 
varying  quantities.  For  nickel  and  cobalt  baths,  an  addition 
of  ammonium  chloride,  in  not  too  small  quantity,  is  most 
suitable,  it  assisting  materially  the  attack  upon  the  contact- 
smetal  and  may  in  some  cases  serve  for  this  purpose  by  itself 
without  the  co-operation  of  an  alkali. 

The  attack  on  the  contact-metal  is  most  effectually  pro- 
moted by  sufficient  alkalinity  of  the  electrolyte,  mostly  in 
connection  with  chlorides,  in  a  few  rarer  cases  without  chlo- 
rides, and  as  previously  mentioned,  occasionally  by  chlorides 
alone  without  the  co-operation  of  an  alkali. 

In  judging  the  formulas  for  contact  baths  to  be  given  later 
•on,  the  effects  here  explained  will  have  to  serve  as  a  basis. 

Small  objects  in  quantities  are  generally  plated  in  baskets 
made  of  the  contact-metal,  and,  as  previously  mentioned,  the 
deposition  of  quantities  of  the  same  metal  with  which  the 
objects  are  to  be  coated  upon  the  contact-body  cannot  be 
avoided.  To  be  sure,  claim  is  made  in  a  few  patents  to  pre- 
vent deposition  upon  the  contact-metal  and  to  keep  the  con- 
tact-body free  by  certain  additions,  for  instance,  alkaline 
pyrophosphates  and  phosphates,  but  experiments  failed  to 
iprove  the  correctness  of  these  claims. 

The  useless  reduction  of  metal  is  one  of  the  many  weak 
'points  of  the  contact-process.  The  bath  thereby  becomes 
xapidly  poor  in  metal,  requires  frequent  refreshing  or  regen- 
eration, which  as  a  rule  is  not  so  readily  done,  and  thus  in 
practice  the  contact-process  becomes  quite  expensive.  It  must 


BY    CONTACT,    BY    BOILING,    AND    BY    FRICTION.  491 

further  be  borne  in  mind  that  so  soon  as  reduction  of  metal 
upon  the  contact-body  takes  place,  the  formation  of  a  deposit 
upon  the  object  ceases,  this  being  the  reason  why  only  very 
thin  deposits  can  be  produced,  which  do  not  afford  protection 
against  atmospheric  influences,  and  are  not  sufficiently  re- 
sistant to  mechanical  attack. 

To  avoid  as  much  as  possible  the  drawback  of, metal  being 
reduced  on  the  wrong  place,  Dr.  G.  Langbein  &  Co.  use,  ac- 
'Cording  to  a  method  for  which  a  patent  has  been  applied  for, 
baskets  of  contact-metal,  the  outsides  of  the  latter,  which  do 
not  come  in  contact  with  the  objects,  being  insulated  from  the 
•electrolyte  by  enameling,  or  coating  with  hard  rubber,  cellu- 
loid or  similar  materials  capable  of  resisting  the  hot  solution. 
Or,  they  use  baskets  of  contact-metal  the  outsides  of  which 
are  provided,  either  mechanically  by  rolling  or  welding,  or 
electrolytically  by  deposition,  with  the  same  metal  contained 
in  solution  in  the  electrolyte,  the  baskets  being  thus  protected 
from  the  deposit ;  while,  in  addition,  a  partial  regeneration  of 
the  bath  is  in  many  cases  attained.  With  certain  combina- 
tions a  portion  of  the  electro-negative  metal  or  alloy  combined 
with  the  contact-metal  or  fixed  insulated  from  it,  passes  into 
solution,  and  partly  replaces  the  metal  which  has  been  with- 
'drawn  from  the  bath  and  deposited  upon  the  objects. 

Further  drawbacks  of  the  contact  process  are,  working  with 
baths  almost  boiling  hot,  and  the  consequent  evolution  of 
steam  which  is  injurious  to  the  workmen  as  well  as  to  the 
work-rooms. 

Hence,  the  contact  process  is  suitable  only  for  coating — so 
to  say  coloring — objects  in  large  quantities  with  another 
metal,  when  no  demands  as  regards  solidity  of  the  deposit  are 
made. 

Nickeling  by  Contact  and  Boiling. 

According  to  Franz  Stolba,  articles  can  be  sufficiently  nick- 
eled in  15  minutes  by  boiling  them,  mixed  with  fragments  of 
zinc  in  a  solution  of  nickel  sulphate.  A  copper  kettle  tinned 


492  ELECTRO-DEPOSITION    OP    METALS. 

inside  is  to  be  used.  Since  stains  are  readily  formed  by  this' 
process,  especially  when  nickeling  polished  iron  and  steel 
articles,  on  the  places  where  the  metal  to  be  nickeled  comes  in 
contact  with  the  zinc,  Stolba  in  later  experiments  omitted  the 
zinc,  and  thus  the  contact  process  becomes  a  boiling  process. 
The  articles  are  to  be  boiled  for  30  to  60  minutes  in  a  10  per 
cent,  zinc  chloride  solution  to  which  is  added  enough  nickel 
sulphate  to  give  the  solution  a  deep  green  color. 

However,  Stolba's  process  cannot  be  recommended  to  the 
nickel-plater.  To  be  sure  a  thin  nickel  deposit  of  a  light 
color  might  be  obtained  upon  brass  articles,  but  that  on  iron 
objects  generally  turned  out  dark  and  mostly  stained.  The 
nickeling  is  so  thin  that  it  will  not  stand  polishing  with  any 
kind  of  pressure,  and  the  cheapness  claimed  for  the  process  is 
quite  illusive,  the  solution  soon  becoming  useless  by  reason 
of  the  absorption  of  copper,  iron,  etc.,  from  the  metals  to  be 
nickeled. 

For  small  articles,  which  are  not  to  be  nickeled  with  the 
assistance  of  the  current,  one  of  the  following  processes  is  to 
be  preferred  : 

By  boiling  a  solution  of  8J  ozs.  of  nickel-ammonium  sul- 
phate and  8J  ozs.  of  ammonium  chloride  in  1  quart  of  water, 
together  with  clean  iron  filings  free  from  grease,  and  introduc- 
ing into  the  fluid  copper  or  brass  articles,  the  latter  become 
coated  with  a  thin  layer  of  nickel  capable  of  bearing  light 
polishing. 

In  place  of  iron  filings,  it  is  of  greater  advantage  to  bring 
the  objects  to  be  coated  in  contact  with  a  piece  of  sheet-zinc 
of  not  too  small  a  surface,  or  to  nickel  them  in  an  aluminium 
basket.  The  hotter  the  solution  is,  the  more  rapidly  coating 
with  nickel  is  effected,  and  when  the  bath  is  made  slightly 
alkaline  with  ammonia,  iron  objects  also  nickel  quite  well  in 
an  aluminium  basket. 

In  place  of  the  zinc  contact,  Basse  &  Selve  use  an  aluminium 
contact  for  nickeling  (as  well  as  for  coppering  and  silvering). 
According  to  the  patent  specification,  objects  nickel  gray  and 


BY    CONTACT,    BY    BOILING,    AND    BY    FRICTION.  493 

show  no  metallic  luster  when  brought  in  a  zinc  basket  into  a 
boiling  solution  of  20  parts  of  nickel-ammonium  sulphate,  40 
parts  ammonium  chloride  and  60  parts  water,  which,  after 
the  addition  of  a  slight  excess  of  ammonia  and  filtering,  is 
rendered  slightly  acid  with  citric  acid.  By  substituting  for 
the  zinc  basket  an  aluminium  basket,  a  lustrous,  more  firmly 
adhering  layer  of  nickel  is  in  about  two  minutes  obtained. 

Still  better  results  are  obtained  by  keeping  the  bath  slightly 
alkaline  with  ammonia  or  ammonium  carbonate. 

A.  Darlay  has  patented  in  France,  as  well  as  in  Germany,  a 
process  of  nickeling  (as  well  as  cobalting)  by  aluminium  or 
magnesium  contact.  However,  the  object  of  the  invention  is 
not  the  aluminium  contact,  which  has  been  known  for  a  long 
time,  nor  the  special  kinds  of  baths,  the  compositions  of  which 
are  similar  to  those  of  other  known  contact-baths,  but  the  use 
of  the  aluminium  or  magnesium  contact  in  connection  with 
baths  of  exactly  defined  compositions. 

These  patented  baths  fulfill  nothing  further  than  the  general 
conditions  given  in  detail  on  p.  487  et  seq.,  and  which  are  also 
fulfilled  by  most  of  the  long  known  contact-baths  as  shown  by 
the  bath  for  gilding  by  contact  (p.  489).  Darlay's  patent  is, 
therefore,  a  combination-patent,  and  its  right  of  existence  ap- 
pears rather  doubtful  in  view  of  the  fact  that  Basse  and  Selve's 
patent  has  expired,  and  that  baths  of  the  composition  of  the 
Darlay  electrolytes  have  long  been  known  and  used  for 
•deposition. 

Darlay's  baths  are  brought  into  commerce  by  "  Electro- 
metallurgie  "  under  the  name  of  autovolt  baths,  and  in  answer 
to  many  inquiries  it  may  here  be  stated  that  for  the  reason 
given  on  p.  488,  no  heavier  deposits  can  be  produced  with 
these  autovolt  baths,  than  with  the  contact  process  in  general, 
and  that  this  autovolt  method  shows  the  same  drawbacks  as 
all  other  contact  processes. 

In  his  patent  specification,  Darlay  gives  the  following  com- 
position of  the  electrolyte  which  is  to  be  used  hot : 

Water  1  quart,  nickel  chloride  7J  drachms,  sodium  phos- 


494  ELECTRO-DEPOSITION    OF    METALS. 

phate  8J  ozs.,  ammonium  chloride  11 J  drachms,  ammonium 
carbonate  and  sodium  carbonate  each  4}  drachms. 

The  sodium  phosphate  is  claimed  to  effect  the  production  of 
a  bright  attacking  surface  of  the  contact-metal,  and  the  sodium 
and  ammonium  carbonates,  the  alkaline  reaction  and,  hence 
the  generation  of  the  current,  by  dissolving  the  aluminium, 
while  the  ammonium  chloride  produces  good  conductivity. 
As  regards  the  action  of  alkaline  pyrophosphates,  the  reader 
is  referred  to  p.  489. 

The  inventor  asserts  that  the  proportions  given  above  have 
to  be  kept  within  quite  narrow  limits.  With  the  exception  of 
the  nickel  chloride,  the  quantities  of  sodium  phosphate  and  of 
one  of  the  other  chemicals  can  without  fear  be  increased  50 
per  cent.,  the  results  thus  obtained  being  still  better  than  with 
Darlay's  formula. 

The  chemical  process  of  Darlay's  electrolyte  consists  no 
doubt  in  that  a  transposition  takes  place  between  the  nickel 
chloride  and  the  sodium  phosphate,  sodium  chloride  and 
nickel  phosphate  being  formed,  which  are  soluble  in  the  excess 
of  sodium  phosphate,  and  are  not  precipitated  by  the  alkaline 
carbonates. 

Hence  the  bath  given  on  p.  259  under  formula  IX  for 
nickeling  with  an  external  source  of  current,  should  be  suit- 
able for  contact-nickeling  with  aluminium,  if  the  quantity  of 
sodium  phosphate  be  materially  increased,  the  conductivity 
enhanced  by  the  addition  of  ammonium  chloride,  and  the  so- 
lution of  the  aluminium  promoted  by  adding  caustic  potash, 
caustic  soda,  or  better,  alkaline  carbonates. 

Cobalting  by  Contact  and  Boiling. 

Cobalting  by  contact  is  readily  accomplished  with  the  use 
of  the  following  bath  :  Crystallized  cobalt  sulphate  0.35  oz., 
crystallized  ammonium  chloride  0.07  oz.,  water  1  quart.  Heat 
the  bath  to  between  104°  and  122°  F.,  and  immerse  the  pre- 
viously cleansed  and  pickled  articles  in  it,  bringing  them  in 
contact  with  a  bright  zinc  surface  not  too  small ;  for  small 


BY    CONTACT,    BY    BOILING,    AND    BY    FRICTION.  495 

articles  a  zinc  basket  may  be  used.  In  3  or  4  minutes  the 
coating  is  heavy  enough  to  bear  vigorous  polishing. 

It  is  a  remarkable  fact  that  with  aluminium-contact  no 
satisfactory  results  are  obtained  in  this  bath,  the  reaction  of 
aluminium  in  cobalt  solutions  thus  appearing  to  be  different 
from  that  in  nickel  solutions.  What  has  been  said  in  re- 
gard to  Darlay's  contact  process  for  nickeling  applies  also  to 
cobalting. 

For  cobalting  small  objects  in  quantities,  the  reader  is  re- 
ferred to  Warren's  process,  p.  324. 

Coppering  by  Contact  and  Dipping. 

According  to  Liidersdorff,  a  solution  of  tartrate  of  copper  in 
neutral  potassium  tartrate  serves  for  this  purpose.  A  suitable 
modification  of  this  bath  is  as  follows  :  Heat  10  quarts  of  water 
to  140°  F.,  add  2  Ibs.  of  pulverized  tartar  (cream  of  tartar) 
free  from  lime,  and  10J  ozs.  of  carbonate  of  copper.  Keep  the- 
fluid  at  the  temperature  above  mentioned  until  the  evolution 
of  gas  due  to  the  decomposition  of  the  carbonate  of  copper 
ceases,  and  then  add  in  small  portions,  and  with  constant  stir- 
ring, pure  whiting  until  effervescence  is  no  longer  perceptible.. 
Filter  off  the  fluid  from  the  tartrate  of  lime,  separate  and  wash 
the  precipitate,  so  that  the  filtrate,  inclusive  of  the  wash  water,, 
amounts  to  10  or  12  quarts,  and  dissolve  in  it  If  ozs.  of  caustic 
soda  and  1  oz.  of  99  per  cent,  potassium  cyanide. 

With  zinc-contact  the  bath  works  somewhat  slowly,  but 
more  rapidly  with  aluminium-contact.  Zinc  is  coppered  in 
this  bath  by  simple  immersion. 

The  bath  for  coppering  by  contact,  proposed  by  Weill,  has 
been  given  on  p.  334,  under  formula  X.  The  bath  is  to  be 
heated  to  between  185°  and  194°  F.,  and  with  zinc  contact 
yields  a  tolerably  good  deposit  upon  small  iron  objects.  With 
aluminium-contact,  iron  screws  as  well  as  iron  articles  in 
quantities  are  quickly  and  nicely  coppered. 

According  to  Bacco,  a  copper  bath  in  which  zinc  may  be 
coppered  by  immersion,  and  iron  and  other  metals  in  contact 


496  ELECTRO-DEPOSITION    OF    METALS. 

"with  zinc,  is  prepared  by  adding  to  a  saturated  solution  of 
blue  vitriol,  potassium  cyanide  solution  until  the  precipitate 
of  cyanide  of  copper  which  is  formed  is  again  dissolved.  Then 
add  -iV  to  -J  of  the  volume  of  liquid  ammonia  and  dilute  with 
water  to  7°  Be. 

The  bath  is  to  be  heated  to  194°  F.  To  the  same  extent 
as  zinc  passes  into  solution  the  copper  bath  is  gradually 
changed  to  a  brass  bath. 

Every  strongly  alkaline  copper  cyanide  bath  may  serve  for 
coppering  by  contact,  provided  only  a  small  quantity  of  free 
potassium  cyanide  is  present  in  the  bath,  and  the  latter  is 
heated  to  194°  F. 

Zinc  when  used  as  a  contact-metal  shows  the  drawback  of 
the  copper  depositing  quite  firmly  upon  it,  so  that  it  has  to 
be  removed  by  pickling  in  nitric  acid.  Furthermore,  with 
the  use  of  zinc  as  contact-bodies,  the  content  of  free  alkali  has 
-to  be  much  larger  than  with  aluminium  contacts,  and  so 
much  zinc  passes,  in  the  first  case,  into  solution  that,  in  place 
of  copper  deposits,  brass  deposits  with  tones  of  color  varying 
according  to  the  temperature  are  in  a  short  time  obtained. 

According  to  Darlay's  patent,  an  alkaline  copper  cyanide 
bath  heated  to  between  185°  and  194°  F.  is  to  be  used,  the 
-electrolyte  consisting  of: 

Water  1  quart,  cupric  sulphate  0.35  oz.,  potassium  cyanide 
0.42  oz.,  caustic  soda  0.52  oz. 

When  in  such  formulas  the  quantity  of  potassium  cyanide 
is  given  without  stating  its  content  in  per  cent.,  it  would,  as  a 
rule,  be  understood  to  refer  to  the  98  or  99  per  cent,  article. 
However,  according  to  experiments  made  with  Bacco's  bath, 
-with  the  use  of  98  per  cent,  potassium  cyanide,  the  excess 
would  be  too  large,  and  it  may  be  supposed  that  Darlay's 
formula  refers  to  60  per  cent,  potassium  cyanide. 

However,  in  this  respect,  the  patent  specification  does  not 

agree  with  the  facts.     For  instance,  the  content  of  potassium 

-cyanide  "is  exactly  to  be  adhered  to"  in  order  to  prevent 

-a  deposit  of  copper  upon  the  contact-body — an  aluminium 


BY    CONTACT,    BY    BOILING,    AND    BY    FRICTION.  497 

basket.  However,  no  matter  whether  potassium  cyanide  with 
a  content  of  60  per  cent.,  or  more  is  used,  a  heavy  deposit  of 
copper  is  always  formed  upon  the  aluminium,*  and  the  for- 
mation of  a  deposit  of  copper  upon  the  objects  is  not  in  the 
least  dependent  upon  adhering  exactly  to  the  quantity  of 
potassium  cyanide  given. 

The  chemical  process  of  Darlay's  formula  consists  therefore 
in  the  conversion  of  cupric  sulphate  and  potassium  cyanide  to 
potassium-copper  cyanide.  With  the  use  of  68  per  cent, 
potassium  cyanide  scarcely  any  free  potassium  cyanide  is 
contained  in  the  bath,  while  with  98  per  cent,  potassium 
cyanide,  free  potassium  cyanide  remains  in  the  bath.  If,  now 
"  the  accurately -fixed  content  of  potassium  cyanide  "  in  Dar- 
lay's formula  refers  to  the  60  per  cent,  article,  we  come  back 
to  Bacco's  formula,  in  which  just  enough  potassium  cyanide 
is  added  to  the  cupric  sulphate  solution  to  redissolve  the  sep- 
arated cupro-cupric  cyanide,  a  content  of  free  potassium 
cyanide  being  avoided.  Bacco  effects  alkalinity  by  ammonia 
and  Darlay  by  caustic  soda.  From  this  it  will  be  seen  that 
Darlay's  formula  is  very  similar  to  Bacco's,  and  it  is  doubtful 
whether  a  patent-right  can  be  claimed  on  the  substitution  of 
caustic  soda  for  ammonia.  At  any  rate,  now  that  Basse  and 
Selve's  patent  has  expired,  it  is  obvious  that  Bacco's  bath 
with  the  use  of  aluminium-contact  can  be  employed  for  cop- 
pering by  contact  without  infringing  on  Darlay's  patent. 

The  so-called  brush-coppering,  which  has  been  recommended, 
may  here  be  mentioned.  This  process  may  be  of  practical 
advantage  for  coppering  very  large  objects  which  by  another 
method  could  only  be  coated  with  difficulty:  The  deposit  of 
copper  is,  of  course,  very  thin.  The  process  is  executed  as 
follows  :  The  utensils  required  are  two  vessels  of  sufficient  size, 
each  provided  with  a  brush,  preferably  so  wide  that  the  entire 
surface  of  the  object  to  be  treated  can  be  coated  with  one  ap- 

*  According  to  experiments  made  by  Friessner,  about  90  per  cent,  of  the  metal 
contained  in  the  bath  was  deposited  upon  the  contact-body,  and  only  10  per  cent, 
the  objects. 

32 


498  ELECTRO-DEPOSITION    OF    METALS. 

plication.  One  of  the  vessels  contains  a  strongly  saturated 
solution  of  caustic  soda,  and  the  other  a  strongly  saturated 
solution  of  blue  vitriol.  For  coppering,  the  well-cleansed 
object  is  first  uniformly  coated  with  a  brushful  of  the  caustic 
soda  solution,  and  then  also  with  a  brushful  of  the  blue  vitriol 
solution.  A  quite  thick  film  of  copper  is  immediately  de- 
posited upon  the  object.  Care  must  be  had  not  to  have  the 
brush  too  full,  and  not  to  touch  the  places  once  gone  over  the 
second  time,  as  otherwise  the  layer  of  copper  does  not  adhere 
firmly. 

Many  iron  and  steel  objects,  for  instance,  wire,  springs,  etc., 
are  provided  with  a  thin  film  of  copper  in  order  to  give  them 
a  more  pleasing  appearance.  For  this  purpose  a  copper  solu- 
tion of  10  quarts  of  water,  If  ozs.  of  blue  vitriol,  and  If  ozs. 
of  pure  concentrated  sulphuric  acid  may  be  used.  Dip  the 
iron  or  steel  objects,  previously  freed  from  grease  and  oxide, 
for  a  moment  in  the  solution,  moving  them  constantly  to  and 
fro ;  then  rinse  them  immediately  in  ample  water,  and  dry. 
By  keeping  the  articles  too  long  in  the  solution  the  copper 
separates  in  a  pulverulent  form,  and  does  not  adhere. 

Steel  pens,  needles1  eyes,  etc.,  may  be  coppered  by  diluting  the 
copper  solution  just  mentioned  with  double  the  quantity  of 
water,  moistening  sawdust  with  the  solution,  and  revolving 
the  latter,  together  with  the  objects  to  be  coppered,  in  a  wooden 
tumbling  barrel. 

Brassing  by  Contact. 

Some  older  authors  have  given  formulas  for  baths  for 
brassing  by  contact,  but  the  results  obtained  are  not  very 
satisfactory. 

Darlay  has  patented  the  bath  given  below.  It  is  brought 
into  commerce  under  the  name  of  autovolt  brass  bath,  and  yields 
thin  brass  deposits  of  an  agreeable  color  and  good  luster  : 

Water  1  quart,  cupric  sulphate  0.14  oz.,  zinc  sulphate  0.35 
oz.,  potassium  cyanide  0.44  oz.,  caustic  soda  0.52  oz. 

On  testing  this  formula  it  was  found  that  with  the  use  of 


BY    CONTACT,    BY    BOILING,    AND    BY    FRICTION.  499 

98  per  cent,  potassium  cyanide  the  bath  yielded  no  deposit, 
one  being,  however,  obtained  with  the  60  per  cent,  article. 
What  has  been  said  in  reference  to  the  autovolt  copper  bath 
applies  also  to  the  brass  bath. 

As  previously  mentioned,  deposits  produced  by  contact  can- 
not be  obtained  of  any  thickness,  the  contact-metal  soon  be- 
coming covered  with  a  deposit  when  the  process  comes  to  a 
standstill.  Aluminium,  to  be  sure,  relinquishes  the  deposited 
metal  in  coherent  laminae,  this  being  promoted  by  the  heavy 
evolution  of  hydrogen.  However,  it  shows  also  how  large 
are  the  quantities  of  metal  which  are  deposited  upon  the  alu- 
minium, and  that  deposition  by  contact  is  consequently  con- 
nected with  a  waste  of  metallic  salts,  which  considerably 
increases  the  cost  of  manufacture.  For  removing  the  deposit 
upon  the  aluminium  body,  mixtures  of  nitric  and  sulphuric 
acids  have  to  be  used,  so  that,  in  addition  to  the  loss  of  metal, 
there  is  a  considerable  consumption  of  acids. 

Iron  objects  brassed  in  the  above-mentioned  baths  have,  to 
be  sure,  quite  a  neat  appearance,  but  soon  commence  to  rust, 
and  for  this  reason  cannot  serve  as  substitutes  for  objects 
thickly  brassed  by  means  of  an  external  source  of  current. 

Silvering  by  Contact,  Immersion  and  Friction. 

For  contact-silvering  of  copper  and  brass  objects  the  follow- 
ing bath  may  be  used  : 

Water  1  quart,  crystallized  silver  nitrate  0.52  oz.,  60  per 
cent,  potassium  cyanide  1.4  ozs. 

The  bath  is  to  be  somewhat  heated,  so  that  deposition  does 
not  take  place  too  slowly.  Zinc  is  very  suitable  for  a  contact- 
metal,  but  to  avoid  formation  of  stains,  the  contact-points 
have  to  be  frequently  changed. 

If  iron  articles  are  to  be  silvered,  it  is  recommended  to  add 
to  the  bath,  heated  to  between  176°  and  194°  F.,  about  0.28 
to  0.35  oz.  of  caustic  soda,  and  to  use  an  aluminium  contact ; 
for  smaller  objects  in  quantities  an  aluminium  basket.  It  is 
of  greater  advantage,  in  all  cases,  first  to  brass  or  copper  the 
iron  objects. 


500  ELECTRO-DEPOSITION    OF    METALS. 

According  to  Darlay's  German  patent,  128,318,  the  follow- 
ing baths  serve  for  silvering  by  contact  with  aluminium  : 

Water  1  liter  (2.11  pints),  silver  nitrate  30  grammes  (0.7 
oz.),  potassium  cyanide  10  grammes  (0.35  oz.),  caustic  potash 
4  grammes  (0.14  oz.). 

Information  regarding  the  content  in  percent,  for  potassium 
cyanide  is  wanting.  Besides,  the  quantity  of  potassium  cya- 
nide in  proportion  to  silver  nitrate  is  too  low,  which  may  be 
due  to  a  typographical  error,  and  it  may  be  supposed  that  the 
formula  for  a  25-liter  bath,  as  given  in  the  patent  specifica- 
tion, should  read  0.05  kilogramme  of  silver  nitrate  instead  of 
0.5  kilogramme.  This,  calculated  to  1  liter,  gives  2  grammes 
instead  of  20  grammes  of  silver  nitrate. 

For  silvering  iron  and  steel  in  hot  baths : 

Water  1  quart,  silver  nitrate  0.44  oz.,  potassium  cyanide 
4.4  ozs.,  sodium  phosphate  0.88  oz. 

The  object  of  the  sodium  phosphate  here  is  not  to  prevent 
the  adhesion  of  the  metal  deposited  upon  the  contact  metal, 
which  is  to  be  effected  by  the  excess  of  potassium  cyanide. 
However,  in  experiments  made  with  this  bath,  more  silver 
was  deposited  upon  the  contact-body  than  upon  the  objects. 

Silvering  by  immersion.  For  silvering  coppered  or  brassed 
objects  by  immersion,  the  following  solution  may  be  used  : 

Water  1  quart,  silver  nitrate  0.35  oz.,  98  per  cent,  potassium 
cyanide  1.23  ozs. 

To  prepare  the  bath  dissolve  the  silver  salt  in  1  pint  of  the 
water,  then  the  potassium  cyanide  in  the  remaining  pint  of 
water,  and  mix  the  two  solutions.  The  bath  is  heated  in  a 
porcelain  or  enameled  iron  vessel  to  between  176°  and  194°  F., 
and  the  thoroughly  cleansed  and  pickled  objects  are  immersed 
in  it  until  uniformly  coated,  previous  quicking  being  not  re- 
quired. The  deposit  is  lustrous  if  the  articles  are  left  but  a 
short  time  in  the  bath,  but  becomes  dull  when  they  remain 
longer.  In  the  first  case  the  deposit  is  a  mere  film,  and,  while 
it  is  somewhat  thicker  in  the  latter,  it  can  under  no  circum- 
stances be  called  solid.  The  thickness  of  the  deposit  does  not 


BY    CONTACT,    BY    BOILING,    AND    BY    FRICTION.  501 

increase  by  continued  action,  as  much  metal  being  dissolved 
as  silver  is  deposited,  and  the  silver  deposit  prevents  a  further 
dissolving  effect  upon  the  basis  metal. 

The  bath  gradually  works  less  effectively,  and  finally  ceases 
to  silver,  when  its  action  may  be  restored  by  the  addition  of 
2|  to  5J  drachms  of  potassium  cyanide  per  quart.  Should 
this  prove  ineffectual,  the  content  of  silver  is  nearly  ex- 
hausted, and  the  bath  is  evaporated  to  dry  ness,  and  the  resi- 
due added  to  the  silver  waste.  Frequent  refreshing  of  the 
bath  with  silver  salt  cannot  be  recommended,  the  silvering 
always  turning  out  best  in  a  fresh  bath. 

A  solution  of  nitrate  of  silver  in  sodium  sulphite  is,  accord- 
ing to  Roseleur,  very  suitable  for  silvering  by  immersion. 
The  solution  is  prepared  by  pouring  into  moderately  concen- 
trated solution  of  sodium  phosphite,  while  constantly  stirring, 
solution  of  a  silver  salt  until  the  precipitate  of  silver  sulphide 
formed  begins  to  be  dissolved  with  difficulty.  The  bath  can 
be  used  cold  or  warm,  fresh  solution  of  silver  being  added 
when  it  commences  to  lose  its  effect.  If,  however,  the  bath  is 
not  capable  of  dissolving  the  silver  sulphide  formed,  concen- 
trated solution  of  sodium  sulphite  has  to  be  added. 

For  the  preparation  of  the  solution  of  sodium  sulphite, 
Roseleur  recommends  the  following  method : 

Into  a  tall  vessel  of  glass  or  porcelain  (Fig.  134)  introduce 
5  quarts  of  water  and  4  pounds  of  crystallized  soda,  after 
pouring  in  mercury  about  an  inch  or  so  deep  to  prevent  the 
glass  tube  through  which  the  sulphurous  acid  is  introduced 
from  being  stopped  up  by  crystals.  The  sulphurous  acid  is 
evolved  by  heating  copper  turnings  with  concentrated  sul- 
phuric acid,  washing  the  gas  in  a  Woulff  bottle  rilled  an  inch 
or  so  deep  with  water,  and  introducing  it  into  the  bottle  con- 
taining the  soda  solution,  as  shown  in  the  illustration.  A 
part  of  the  soda  becomes  transformed  into  sodium  sulphite, 
which  dissolves,  and  a  part  is  precipitated  as  carbonate.  The 
latter,  however,  is  transformed  into  sodium  sulphite  by  the 
continuous  action  of  sulphurous  acid,  and  carbonic  acid  gas 


502  ELECTRO-DEPOSITION    OF    METALS. 

escapes  with  effervescence.  When  all  has  become  dissolved, 
the  introduction  of  sulphurous  acid  should  be  continued  until 
the  liquid  slightly  reddens  blue  litmus  paper,  when  it  is  set 
aside  for  24  hours.  At  the  end  of  that  time  a  certain  quan- 
tity of  crystals  will  be  found  upon  the  mercury,  and  the  liquid 
above,  more  or  less  colored,  constitutes  the  sodium  sulphite  of 
the  silvering  bath.  The  liquid  sodium  sulphite  thus  prepared 
should  be  stirred  with  a  glass  rod,  to  eliminate  the  carbonic 
acid  which  may  still  remain  in  it.  The  liquid  should  then 
be  again  tested  with  blue  litmus  paper,  and  if  the  latter  is 
strongly  reddened,  carbonate  of  soda  is  cautiously  added,  little 

FIG.  134. 


by  little,  in  order  to  neutralize  the  excess  of  sulphurous  acid. 
On  the  other  hand,  if  red  litmus  paper  becomes  blue,  too 
much  alkali  is  present,  and  more  sulphurous  acid  gas  must  be 
passed  through  the  liquid,  which  is  in  the  best  condition  for 
our  work  when  it  turns  litmus  paper  violet  or  slightly  red. 
The  solution  should  mark  from  22°  to  20°  Be.,  and  should 
not  come  in  contact  with  iron,  zinc,  tin,  or  lead. 

As  will  be  seen,  this  mode  of  preparing  the  sodium  sulphite 
solution  is  somewhat  troublesome,  and  it  is  therefore  recom- 
mended to  proceed  as  follows :  Prepare  a  saturated  solution  of 


BY    CONTACT,    BY    BOILING,    AND    BY    FRICTION.  503 

commercial  sodium  sulphite.  The  solution  will  show  an  alka- 
line reaction,  the  commercial  salt  frequently  containing  some 
sodium  carbonate.  To  this  solution  add,  while  stirring,  solu- 
tion of  bisulphite  of  sodium  saturated  at  122°  F.,  until  blue 
litmus  paper  is  slightly  reddened.  Then  add  to  this  solution 
concentrated  solution  of  nitrate  of  silver  until  the  flakes  of 
silver  sulphide  separated  begin  to  dissolve  with  difficulty. 

The  immersion-bath,  prepared  according  to  one  or  the  other 
method,  works  well,  the  silvering  produced  having  a  beautiful 
luster,  such  as  is  desirable  for  many  cheap  articles.  If  the 
articles  are  allowed 'to  remain  for  a  longer  time  in  the  bath,  a 
mat  deposit  is  obtained.  For  bright  silvering,  the  bath 
should  always  be  used  cold.  It  must  further  be  protected  as 
much  as  possible  from  the  light,  otherwise  decomposition 
gradually  takes  place. 

According  to  Dr.  Ebermayer,  a  silver  immersion-bath  for 
bright  silvering  is  prepared  as  follows:  Dissolve  1.12  ozs.  of 
nitrate  of  silver  in  water,  and  precipitate  the  solution  with 
caustic  potash.  Thoroughly  wash  the  silver  oxide  which  is 
precipitated,  and  dissolve  it  in  1  quart  of  water  which  con- 
tains 3.52  ozs.  of  potassium  cyanide  in  solution,  and  finally 
dilute  the  whole  with  one  quart  more  water.  For  silvering, 
the  bath  is  heated  to  the  boiling-point,  and  the  silver  with- 
drawn may  be  replaced  by  the  addition  of  moist  silver  oxide 
as  long  as  complete  solution  takes  place.  When  the  silvering 
is  no  longer  beautiful  and  of  a  pure  white  color,  the  bath  is 
useless,  and  is  then  evaporated.  Experiments  with  a  bath 
prepared  according  to  the  above  directions  were  never  quite 
satisfactory.  Better  results  were,  however,  obtained  by  dilu- 
ting the  bath  with  3  to  4  quarts  of  water  and  using.it  without 
heating.  It  then  yielded  very  nice,  lustrous  silvering. 

The  process  of  coating  with  a  thin  film,  or  rather  whitening, 
with  silver,  small  articles,  such  as  hooks  and  eyes,  pins,  etc., 
differs  from  the  above-described  immersion  method,  which 
effects  the  silvering  in  a  few  seconds,  in  that  the  articles  re- 
quire to  be  boiled  for  a  longer  time.  The  process  is  as  follows : 


504  ELECTRO-DEPOSITION    OF    METALS. 

Prepare  a  paste  from  0.88  oz.  of  silver  nitrate  precipitated 
as  silver  chloride,  cream  of  tartar  44  ozs.  and  a  like  quantity 
of  common  salt,  by  precipitating  the  silver  nitrate  with  hydro- 
chloric acid,  washing  the  chloride  of  silver  and  mixing  it  with 
the  above-mentioned  quantities  of  cream  of  tartar  and  common 
salt,  and  sufficient  water  to  a  paste,  which  is  kept  in  a  dark 
glass  vessel  to  prevent  the  chloride  of  silver  from  being  decom- 
posed by  the  light.  Small  articles  of  copper  or  brass  are  first 
freed  from  grease  and  pickled.  Then  heat  in  an  enameled 
kettle  3  to  5  quarts  of  rain-water  to  the  boiling-point ;  add  2 
or  3  heaping  teaspoonfuls  of  the  above-mentioned  paste,  and 
bring  the  metallic  objects  contained  in  a  stoneware  basket  into 
the  bath,  and  stir  them  diligently  with  a  rod  of  glass  or  wood. 
Before  placing  a  fresh  lot  of  articles  in  the  bath,  additional  sil- 
ver paste  must  be  added.  If  finally  the  bath  acquires  a  green- 
ish color,  caused  by  dissolved  copper,  it  is  no  longer  suitable 
for  the  purpose,  and  is  then  evaporated  and  added  to  the  sil- 
ver residues. 

Cold  silvering  with  paste. — In  this  process  an  argentiferous- 
paste,  composed  as  given  below,  is  rubbed,  by  means  of  the 
thumb,  a  piece  of  soft  leather,  or  rag,  upon  the  cleansed  and 
pickled  metallic  surface  (copper,  brass,  or  other  alloys  of  cop- 
per) until  it  is  entirely  silvered.  The  paste  may  also  be  rubbed 
in  a  mortar  with  some  water  to  a  uniformly  thin-fluid  mass,  and 
applied  with  a  brush  to  the  surface  to  be  silvered.  By  allow_ 
ing  the  paste  to  dry  naturally,  or  with  the  aid  of  a  gentle 
heat,  the  silvering  appears.  The  application  of  the  paste  by 
means  of  a  brush  is  chiefly  made  use  of  for  decorating  with 
silver,  articles  thinly  gilded  by  immersion.  For  articles  not 
gilded,  the  above-mentioned  rubbing-on  of  the  stiff  paste  is  to- 
be  preferred. 

Composition  of  argentiferous  paste. — I.  Silver  in  the  form  of 
freshly  precipitated  chloride  of  silver,*  0.352  oz.,  common 
salt  0.35  oz.,  potash  0.7  oz.,  whiting  0.52  oz.  and  water  a  suffi- 
cient quantity  to  form  the  ingredients  into  a  stiff  paste. 

II.  Silver  in  the  form  of  freshly  precipitated  chloride  of  sil- 


BY    CONTACT,    BY    BOILING,    AND    BY    FRICTION.  505 

ver  *  0.35  oz.,  potassium  cyanide  1.05  ozs.,  sufficient  water  to 
dissolve  these  two  ingredients  to  a  clear  solution,  and  enough 
whiting  to  form  the  whole  into  a  stiff  paste.  This  paste  is 
also  excellent  for  polishing  tarnished  silver  ;  it  is,  however, 
poisonous. 

The  following  non-poisonous  composition  does  excellent 
service:  Silver  in  the  form  of  chloride  of  silver  0.35  oz., 
cream  of  tartar  0.7  oz.,  common  salt  0.7  oz.,  and  sufficient 
water  to  form  the  mixture  of  the  ingredients  into  a  stiff  paste. 

Another  composition  is  as  follows  :  Chloride  of  silver  1  part, 
pearl  ash  3,  common  salt  1J,  whiting  1,  and  sufficient  water 
to  form  a  paste.  Apply  the  latter  to  the  metal  to  be  silvered 
and  rub  with  a  piece  of  soft  leather.  When  the  metal  is  sil- 
vered, wash  in  water,  to  which  a  small  quantity  of  washing 
soda  has  been  added. 

Graining. — In  gilding  parts  of  watches,  gold  is  seldom  di- 
rectly applied  upon  the  copper  ;  there  is  generally  a  prelim- 
inary operation  called  graining,  by  which  a  grained  and 
slightly  dead  appearance  is  given  to  the  articles.  Marks  of 
the  file  are  obliterated  by  rubbing  upon  a  whetstone,  and 
lastly  upon  an  oil  stone.  Any  oil  or  grease  is  removed  by 
boiling  the  parts  for  a  few  minutes  in  a  solution  of  10  parts 
of  caustic  soda  or  potash  in  100  of  water,  which  should  wet 
them  entirely  if  all  the  oil  has  been  removed.  The  articles 
being  threaded  upon  a  brass  wire,  cleanse  them  rapidly  in  the 
acid  mixture  for  a  bright  luster,  and  dry  them  carefully  in 
white  wood  sawdust.  The  pieces  are  fastened  upon  the  even 
side  of  a  block  of  cork  by  brass  pins  with  flat  heads.  The 
parts  are  then  thoroughly  rubbed  over  with  a  brush  entirely 
free  from  grease,  and  dipped  into  a  paste  of  water  and  very 
fine  pumice-stone  powder.  Move  the  brush  in  circles,  in  order 
not  to  rub  one  side  more  than  the  other ;'  thoroughly  rinse  in 
cold  water,  and  no  particle  of  pumice-stone  should  remain 
upon  the  pieces  of  cork.  Next  place  the  cork  and  the  pieces- 

*  From  0.56  oz.  of  nitrate  of  silver. 


•506  ELECTRO-DEPOSITION    OF    METALS. 

in  a  weak  mercurial  solution,  composed  of  water  2J  gallons, 
nitrate  or  binoxide  of  mercury  y¥  oz.,  sulphuric  acid  |  oz.? 
which  slightly  whitens  the  copper.  The  pieces  are  passed 
-quickly  through  the  solution  and  then  rinsed.  This  opera- 
tion gives  strength  to  the  graining,  which  without  it  possesses 
no  adherence. 

The  following  preparations  may  be  used  for  graining :  I. 
Silver  in  impalpable  powder  2  ozs.,  finely-pulverized  cream  of 
tartar  20  ozs.,  common  salt  4  Ibs.  II.  Silver  powder  1  oz., 
<;ream  of  tartar  4  to  5  ozs.,  common  salt  13  ozs.  III.  Silver 
powder,  common  salt,  and  cream  of  tartar,  equal  parts  by 
weight  of  each.  The  mixture  of  the  three  ingredients  must 
be  thorough  and  effected  at  a  moderate  and  protracted  heat. 
The  graining  is  the  coarser  the  more  common  salt  there  is  in 
the  mixture,  and  it  is  the  finer  and  more  condensed  as  the  pro- 
portion of  cream  of  tartar  is  greater,  but  it  is  then  more  diffi- 
cult to  scratch-brush.  The  silver  powder  is  obtained  as  follows: 
Dissolve  in  a  glass  or  porcelain  vessel  f  oz.  of  crystallized 
nitrate  of  silver  in  2J  gallons  of  distilled  water,  and  place  5 
or  6  ribbands  of  cleansed  copper,  f  inch  wide,  in  the  solution. 
These  ribbands  should  be  long  enough  to  allow  of  a  portion  of 
them  being  above  the  liquid.  The  whole  is  kept  in  a  dark 
place,  and  from  time  to  time  stirred  with  the  copper  ribbands. 
This  motion  is  sufficient  to  loosen  the  deposited  silver,  and 
present  fresh  surfaces  to  the  action  of  the  liquor.  When  no 
more  silver  deposits  on  the  copper  the  operation  is  complete, 
and  there  remains  a  blue  solution  of  nitrate  of  copper.  The 
-silver  powder  is  washed  by  decantation  or  upon  a  filter  until 
there  remains  nothing  of  the  copper  solution. 

For  the  purpose  of  graining,  a  thin  paste  is  made  of  one  of 
the  above  mixtures  and  water,  and  spread  by  means  of  a  spatula 
upon  the  watch  parts  held  upon  the  cork.  The  cork  itself  is 
placed  upon  an  earthenware  dish,  to  which  a  rotating  move- 
ment is  imparted  by  the  left  hand.  An  oval  brush  with  close 
bristles,  held  in  the  right  hand,  rubs  the  watch  parts  in  every 
•direction,  but  always  with  a  rotary  motion.  A  new  quantity 


BY    CONTACT,    BY    BOILING,    AND    BY    FRICTION.  507 

•of  paste  is  added  two  or  three  times  and  rubbed  in  the  manner 
indicated.  The  more  the  brush  and  cork  are  turned,  the 
rounder  becomes  the  grain,  which  is  a  good  quality,  and  the 
more  paste  added,  the  larger  the  grain.  When  the  desired 
grain  is  obtained,  the  pieces  are  washed  and  scratch-brushed. 
The  brushes  employed  are  of  brass  wire,  as  fine  as  hair,  and 
very  stiff  and  springy.  It  is  necessary  to  anneal  them  upon 
an  even  fire  to  different  degrees ;  one  soft  or  half  annealed  for 
the  first  operation  or  uncovering  the  grain  ;  one  harder  for 
bringing  up  the  luster;  and  one  very  soft  or  fully  annealed, 
used  before  gilding  for  removing  any  marks  which  may  have 
been  made  by  the  preceding  tool,  and  for  scratch-brushing 
after  gilding,  which,  like  the  graining,  must  be  done  by  giv- 
ing a  rotary  motion  to  the  tool.  If  it  happens  that  the  same 
watch  part  is  composed  of  copper  and  steel,  the  latter  metal 
requires  to  be  preserved  against  the  action  of  the  cleansing 
acids  and  of  the  graining  mixture  by  a  composition  called 
resist.  This  consists  in  covering  the  pinions  and  other  steel 
parts  with  a  fatty  composition  which  is  sufficiently  hard  to 
resist  the  tearing  action  of  the  bristle  and  wire  brushes,  and 
insoluble  in  the  alkalies  of  the  gilding  bath.  A  good  compo- 
sition is  :  Yellow  wax,  2  parts  by  weight ;  translucent  rosin, 
3J  ;  extra-fine  red  sealing-wax,  1J  ;  polishing  rouge,  1.  Melt 
the  rosin  and  sealing-wax  in  a  porcelain  dish,  upon  a  water- 
bath,  and  afterwards  add  the  yellow  wax.  When  the  whole 
is  thoroughly  fluid,  gradually  add  the  rouge  and  stir  with  a 
wooden  or  glass  rod,  withdraw  the  heat,  but  continue  the  stir- 
ring until  the  mixture  becomes  solid,  otherwise  all  the  rouge 
will  fall  to  the  bottom.  The  flat  parts  to  receive  this  resist 
are  slightly  heated,  and  then  covered  with  the  mixture,  which 
melts  and  is  easily  spread.  For  covering  steel  pinions  employ 
a  small  gouge  of  copper  or  brass  fixed  to  a  wooden  handle. 
The  metallic  part  of  the  gouge  is  heated  upon  an  alcohol 
lamp  and  a  small  quantity  of  resist  is  taken  with  it.  The 
composition  soon  melts,  and  by  turning  the  tool  around,  the 
steel  pinion  thus  becomes  coated.  Use  a  scratch-brush  with 


508  ELECTRO-DEPOSITION    OF    METALS. 

long  wires,  and  their  flexibility  prevents  the  removal  of  the 
composition.  When  the  resist  is  to  be  removed  after  gilding, 
put  the  parts  into  warm  oil  or  tepid  turpentine,  then  in  a  very 
hot  soap-water  or  alkaline  solution  ;  and,  lastly,  into  fresh 
water.  Scratch-brush  and  dry  in  warm,  white  wood  saw-dust. 
The  holes  of  the  pinions  are  cleansed  and  polished  with  small 
pieces  of  very  white,  soft  wood,  the  friction  of  which  is  suffi- 
cient to  restore  the  primitive  luster.  The  gilding  of  parts  of 
copper  and  steel  requires  the  greatest  care,  as  the  slightest  rust 
destroys  their  future  usefulness.  Should  some  gold  deposit 
upon  the  steel,  it  should  be  removed  by  rubbing  with  a  piece 
of  wood  and  impalpable  pumice  dust,  tin  putty,  or  rouge. 

The  gilding  of  the  grained  watch  parts  is  effected  in  a  bath 
prepared  according  to  formula  I  or  III,  given  under  "  Deposi- 
tion of  Gold." 

Gilding  by  Contact,  by  Immersion,  and  by  Friction. 

For  contact-gilding  by  touching  with  zinc,  formulas  I,  II, 
IV  and  V,  given  in  Chapter  IX  "  Deposition  of  Gold  "  may 
be  used,  IV  and  V  being  especially  suitable,  if  the  addition 
of  potassium  cyanide  is  somewhat  increased  and  the  baths  are 
sufficiently  heated. 

A  contact  gold  bath  prepared  with  yellow  prussiate  of 
potash  according  to  the  following  formula  also  yields  a  good 
deposit. 

I.  Fine  gold  as  chloride  of  gold  54  grains,  yellow  prussiate 
of  potash  1  oz.,  potash  1  oz.,  common  salt  1  oz.,  water  1  quart. 

The  bath  is  prepared  as  given  for  formula  III  under 
"  Deposition  of  Gold."  For  use,  heat  it  to  boiling. 

II.  Chemically  pure  crystallized  sodium  phosphate  2.11  ozs., 
neutral  crystallized  sodium  sulphite  0.35  oz.,  potassium  cya- 
nide 0.28  oz.,  fine  gold  (as  chloride)  15.43  grains,  water  1 
quart. 

The  bath  is  prepared  as  given  for  formula  V  under  "  Depo- 
sition of  Gold."  Temperature  for  contact-gilding  185°  to 
194°  F.  If  red  gilding  is  to  be  effected  in  this  bath  a  corres- 


BY    CONTACT,    BY    BOILING,    AND    BY    FRICTION.  509 

ponding  addition  of  potassium-copper  cyanide  has  to  be  made, 
7J  grains  sufficing  for  paler  red,  while  15  grains  have  to  be 
added  for  redder  tones. 

Gilding  by  contact  is  done  the  same  way  as  silvering  by 
contact.  The  points  of  contact  must  be  frequently  changed, 
since  in  the  gold  bath  intense  stains  are  still  more  readily 
formed  than  in  the  silver  bath. 

Gilding  by  immersion  (without  battery  or  contact).  The  fol- 
lowing two  formulas  have  proved  very  useful : 

I.  Crystallized  sodkim  pyrophosphate2.82  ozs.,  12  percent, 
prussic  acid  4.&1   drachms,  crystallized  chloride  of  gold  1.12 
drachms,  water  1  quart.     Heat  the  bath  to  the  boiling-point, 
and  immerse  the  pickled  objects  of  copper  or  its  alloys,  mov- 
ing them  constantly  until  gilded.     Iron,  steel,  tin,  and   zinc 
should  be  previously  coppered,  coating  the  objects  with  mer- 
cury (quicking)  being  entirely  superfluous. 

All  gold  baths  prepared  with  sodium  pyrophosphate,  when 
fresh,  give  rapid  and  beautiful  results,  but  they  have  the  dis- 
advantage of  rapidly  decomposing,  and  consequently  can 
seldom  be  completely  exhausted.  In  this  respect  the  follow- 
ing formula  answers  much  better. 

II.  Crystallized    sodium    phosphate    2.82    drachms,   chem- 
ically pure  caustic  potash  1.69  drachms,  chloride  of  gold  0.56 
drachm,  98  per  cent,  potassium  cyanide  9.03  drachms,  water 
1  quart.     Dissolve  the  sodium   phosphate  and  caustic  potash 
in  }  of  the  water,  and  the  potassium  cyanide  and  chloride  of 
gold  in  the  remaining  J,  and  mix  both  solutions.     Heat  the 
solution  to  the  boiling-point.     This  bath  can  be  almost  entirely 
exhausted,  as  it  is  not  decomposed  by  keeping.     Should  the 
bath  become  weak,  add  about  2f  drachms  of  potassium  cya- 
nide, and  use  it  for  preliminary  dipping  until  no  more  gold 
is  reduced.     To  complete  gilding,  the  objects  subjected  to  such 
preliminary  dipping  are  then  immersed  for  a  few  seconds  in  a 
freshly  prepared  bath  of  the  composition  given  above. 

The  bath  prepared  according  to  formula  II  is  also  very 
suitable  for  contact  gilding. 


510  ELECTRO-DEPOSITION    OF    METALS. 

The  layer  of  gold  produced  by  immersion  is*  in  all  cases 
very  thin,  since  only  as  much  gold  is  deposited  as  corresponds 
to  the  quantity  of  basis-metal  dissolved.  For  heavier  gilding 
by  this  process  the  action  of  zinc  or  aluminium  contact  will 
have  to  be  employed  as  auxiliary  means. 

Gilding  by  friction.  This  process  is  variously  termed  gilding 
with  the  rag,  with  the  thumb,  with  the  cork.  It  is  chiefly  em- 
ployed upon  silver,  though  sometimes  also  upon  brass  and 
copper.  The  operation  is  as  follows:  Dissolve  1.12  to  1.69 
drachms  of  chloride  of  gold  in  as  little  water  as  possible,  to- 
which  has  previously  been  added  0.56  drachm  of  saltpetre. 
Dip  in  this  solution  small  linen  rags,  and,  after  allowing  them 
to  drain  off,  dry  them  in  a  dark  place.  These  rags  saturated 
with  gold  solution  are  then  charred  to  tinder  at.  not  too  great 
a  heat,  whereby  the  chloride  of  gold  is  reduced,  partially  to 
protochloride  and  partially  to  finely-divided  metallic  gold. 
This  tinder  is  then  rubbed  in  a  porcelain  mortar  to  a  fine, 
uniform  powder. 

To  gild  with  this  powder,  dip  into  it  a  charred  cork  moist- 
ened with  vinegar  or  salt  water  and  rub,  with  not  too  gentle  a 
pressure,  the  surface  of  the  article  to  be  gilded,  which  must 
be  previously  cleansed  from  adhering  grease.  The  thumb  of 
the  hand  may  be  used  in  place  of  the  cork,  but  in  both  cases 
care  must  be  had  not  to  moisten  it  too  much,  as  otherwise  the 
powder  takes  badly.  After  gilding,  the  surface  may  be  care- 
fully burnished. 

Reddish  gilding  by  friction  is  obtained  by  adding  about  8 
grains  of  cupric  nitrate  to  the  gold  solution. 

For  gilding  by  friction,  a  solution  of  chloride  of  gold  in  an 
excess  of  potassium  cyanide  may  also  be  used,  after  thicken- 
ing the  solution  to  a  paste  by  rubbing  in  whiting.  The  paste 
is  applied  to  the  previously  zincked  metals  by  means  of  a  cork, 
a  piece  of  leather  or  a  brush.  Martin  and  Peyraud,  the  orig- 
inators of  this  method,  describe  the  operation  as  follows : 
Articles  of  other  metals  than  zinc  are  placed  in  a  bath  consist- 
ing of  concentrated  solution  of  ammonium  chloride,  in  which 


BY    CONTACT,    BY    BOILING,    AND    BY    FRICTION.  511 

has  been  placed  a  quantity  of  granulated  zinc.  The  articles- 
are  allowed  to  boil  a  few  minutes,  whereby  they  acquire  a 
coating  of  zinc.  For  the  preparation  of  the  gilding  composi- 
tion, dissolve  11.28  drachms  of  chloride  of  gold  in  a  like- 
quantity  of  water,  and  add  a  solution  of  2.11  ozs.  of  potassium 
cyanide  in  as  little  water  as  possible  (about  2.8  ozs.).  Of  this 
solution  add  so  much  to  a  mixture  of  3.52  ozs.  of  fine  whiting 
and  2.82  drachms  of  pulverized  tartar  that  a  paste  is  formed 
which  can  be  readily  applied  with  a  brush  to  the  article  to  be 
gilded.  When  the  article  is  coated,  heat  it  to  between  140° 
and  158°  F.  After  removing  the  dry  paste  by  washing,  the 
gilding  appears  and  can  be  polished  with  the  burnisher. 

Platinizing  by  contact. 

Though  a  thick  deposit  cannot  be  produced  by  the  contact- 
process,  Fehling's  directions  may  here  be  mentioned  as  suit- 
able for  giving  a  thin  coat  of  platinum  to  fancy  articles.  He 
recommends  a  solution  of  0.35  oz.  of  chloride  of  platinum  and 
7  ozs.  of  common  salt  in  1  quart  of  water,  which  is  made  alka- 
line by  the  addition  of  a  small  quantity  of  soda  lye,  and  for 
use  heated  to  the  boiling-point. 

If  larger  articles  are  to  be  platinized  by  contact,  free  them 
from  grease,  and  after  pickling,  and  if  necessary,  coppering, 
wrap  them  round  with  zinc  wire,  or  place  them  upon  a  bright 
zinc  sheet,  and  introduce  them  into  the  heated  bath.  All  the 
remaining  manipulations  are  the  same  as  in  other  contact- 
processes. 

Tinning  by  Contact  and  by  Boiling. 

For  tinning  by  zinc-contact  in  the  boiling  tin  bath,  the  follow- 
ing solutions  are  suitable  : 

According  to  Gerhold  :  Pulverized  tartar  and  alum,  of  each 
3.5  ozs.,  fused  stannous  chloride  0.88  oz.,  rain-water  10  quarts. 

According  to  Roseleur :  Potassium  pyrophosphate  7  ozs., 
crystallized  stannous  chloride  (tin-salt)  0.38  oz.,  fused  stan- 
nous chloride  2.8  ozs.,  rain-water  10  quarts. 


512  ELECTRO-DEPOSITION    OP    METALS. 

It  might  be  advisable  to  increase  the  content  of  potassium 
pyrophosphate,  and  to  add  about  0.7  oz.  of  caustic  soda. 

According  to  Roseleur  by  immersion  : 

Potassium  pyrophosphate  5.6  ozs.,  fused  stannous  chloride 
1.23  ozs.,  rain-water  10  quarts. 

For  tinning  by  contact,  heat  the  bath  to  boiling  and  suspend 
the  clean  and  pickled  objects  in  contact  with  pieces  of  zinc^ 
•or,  better,  wrapped  around  with  zinc  wire  spirals,  care  being 
had  from  time  to  time  to  shift  them  about  to  prevent  staining. 
Large  baths  which  cannot  be  readily  heated  are  worked  cold, 
the  objects  being  covered  with  a  large  zinc  plate.  In  the  cold 
bath  the  formation  of  the  tin  deposit  requires,  of  course,  a 
longer  time.  By  using  the  electric  current  the  deposit  can  be 
made  as  heavy  as  desired.  By  immersion  in  the  bath  pre- 
pared according  to  the  last  formula,  zinc  can  only  be  coated 
with  a  very  thin  film  of  tin. 

For  tinning  by  contact  in  a  cold  bath,  Zilken  has  patented 
the  following  solution  :  Dissolve  with  the  aid  of  heat  in  100 
•quarts  of  water,  tin-salt  7  to  10.5  ozs.,  pulverized  alum  10.5 
ozs.,  common  salt  15f  ozs.,  and  pulverized  tartar  7  ozs.  The 
cold  solution  forms  the  tin  bath.  The  objects  to  be  tinned 
are  to  be  wrapped  round  with  strips  of  zinc.  Duration  of  the 
process,  8  to  10  hours. 

Darlay  uses  for  a  cold  tin  bath  with  aluminium-contact : 

Water  10  quarts,  stannous  chloride  1.05  ozs.,  potassium 
-cyanide  1.41  ozs.,  caustic  soda  1.76  ozs. 

It  might  be  advisable  to  heat  the  bath  to  at  least  between 
113°  and  122°  F.  For  a  hot  tin  bath  Darlay  uses  : 

Water  10  quarts,  stannous  chloride  0.88  oz.,  potassium  cya- 
nide 10.58  ozs.,  caustic  soda  0.88  oz.,  sodium  pyrophosphate 
8.8  ozs. 

The  contact-body  cannot  be  kept  free  from  deposit  by  the 
addition  of  potassium  cyanide,  and  tinning  is  effected  as  well 
without  as  with  the  addition  of  potassium  cyanide. 

Tinning  solution  for  iron  and  steel  articles.  Crystallized 
-ammonium-alum  7  ozs.,  crystallized  stannous  chloride  2.8 


BY    CONTACT,    BY    BOILING,    AND    BY    FRICTION.  513 

drachms,  fused  stannous  chloride  2.8  drachms,  rain-water  10 
quarts.  Dissolve  the  ammonium-alum  in  the  hot  water,  and 
when  dissolved  add  the  tin-salts.  The  bath  is  to  be  used  boil- 
ing hot  and  kept  at  its  original  strength  by  an  occasional  ad- 
dition of  tin-salt.  The  clean  and  pickled  iron  objects,  after 
being  immersed  in  the  bath,  become  in  a  few  seconds  coated 
with  a  firmly-adhering  film  of  tin  of  a  dead,  white  color,  which 
may  be  polished  by  scratch-brushing,  or  scouring  with  saw- 
dust in  the  tumbling  barrel.  Tinning  by  boiling  in  the  above 
bath  is  the  most  suitable  preparation  for  iron  arid  steel  objects 
which  are  finally  to  be  provided  with  a  heavy  electro-deposit 
of  tin.  To  insure  entire  success  it  is  recommended  thoroughly 
to  scratch-brush  the  objects  after  boiling,  then  to  return  them 
once  more  to  the  bath,  and  finally  to  suspend  them  in  a  bath 
composed  according  to  formula  I,  Ila  or  III,  given  under 
11  Deposition  of  Tin." 

A  tinning  solution  for  small  brass  and  copper  articles  (pins, 
eyes,  hooks,  etc.),  consists  of  a  boiling  solution  of:  Pulverized 
tartar  3.5  ozs.,  stannous  chloride  (tin-salt)  14.11  drachms, 
water  10  quarts.  After  heating  the  bath  to  the  boiling-point, 
immerse  the  objects  to  be  tinned  in  a  tin  basket,  or  in  contact 
with  pieces  of  zinc  in  a  stoneware  basket.  Frequent  stirring 
with  a  tin  rod  shortens  the  process. 

A  tinning  solution  highly  recommended  by  Roseleur  con- 
sists of : 

Crystallized  sodium  pyrophosphate  7  ozs.,  crystallized  stan- 
nous chloride  0.7  oz.,  fused  stannous  chloride  2.82  ozs.,  water 
10  quarts. 

The  solution  is  prepared  in  the  same  manner  as  the  preced- 
ing one. 

Another  solution,  given  by  Bottger,  also  yields  good  results : 
Dissolve  oxide  of  tin  by  boiling  with  potash  lye,  and  place  the 
copper  or  brass  objects  to  be  tinned  in  the  boiling  solution  in 
contact  with  tin  shavings. 

Eisner's  bath  yields  equally  good  results.     It  consists  of  a  so- 
lution of  equal  parts  of  tin-salt  and  common  salt  in  rain-water. 
The  manipulation  is  the  same  as  given  above. 
33 


514  ELECTRO-DEPOSITION    OF    METALS. 

A  characteristic  method  of  tinning  by  Stolba  is  as  follows  : 
Prepare  a  solution  of  1.75  ozs.  of  tin-salt  and  5.64  drachms  of 
pulverized  tartar  in  one  quart  of  water.  Moisten  with  this  so- 
lution a  small  sponge  and  dip  the  latter  into  pulverulent  zinc. 
By  then  rubbing  the  thoroughly  cleansed  and  pickled  articles 
with  the  sponge,  they  immediately  become  coated  with  a  film 
of  tin.  To  obtain  uniform  tinning,  the  sponge  must  be  re- 
peatedly dipped,  now  into  the  solution,  and  then  into  the  zinc- 
powder,  and  the  rubbing  continued  for  a  few  minutes. 

\ 

Zincking  by  Contact. 

For  zincking  iron  by  contact,  a  concentrated  solution  of  zinc 
chloride  and  ammonium  chloride  in  water  is  very  suitable. 
The  objects  are  placed  in  the  solution  in  contact  with  a  large 
zinc  surface. 

Darlay  (German  patent  128319)  gives  the  following  bath 
which,  with  an  aluminium  contact  is  claimed  to  yield  a  useful 
coating  of  zinc : 

Water  10  quarts,  zinc  sulphate  0.35  ozs.,  potassium  cyanide 
1  oz.,  caustic  soda  5.29  ozs. 

It  may  be  supposed  that  the  bath  is  to  be  heated  to  between 
170°  and  194°  F.,  though  the  patent  specification  is  silent  on 
this  point.  Experiments  to  obtain,  according  to  these  direc- 
tions, a  good  coating  of  zinc  on  iron  did  not  yield  satisfactory 
results. 

To  coat  brass  and  copper  with  a  bright  layer  of  zinc  proceed 
as  follows  :  Boil  for  several  hours  commercial  zinc-gray,  i.  e., 
very  finely-divided  metallic  zinc,  with  concentrated  solution 
of  caustic  soda.  Then  immerse  the  articles  to  be  zincked  in 
the  boiling  fluid,  when,  by  continued  boiling,  they  will  in  a 
short  time  become  coated  with  a  very  bright  layer  of  zinc. 
When  a  copper  article  thus  coated  with  zinc  is  carefully 
heated  in  an  oil  bath  to  between  248°  and  284°  F.,  the  zinc 
alloys  with  the  copper,  forming  a  sort  of  bronze  similar  to 
tombac. 


BY    CONTACT,    BY    BOILING,    AND    BY    FRICTION.  515 

Depositions  of  Antimony  and  of  Arsenic  by  Immersion. 

A  heated  solution  of  chloride  of  antimony  in  hydrochloric 
acid — liquor  stibii  chlorati  of  commerce — deposits  upon  brass 
objects  immersed  in  it  a  coating  of  antimony  of  a  steel-gray 
color  inclining  to  bluish. 

A  purer  steel-gray  color  is  obtained  with  the  use  of  a  hot 
solution  of  arsenious  chloride  in  water. 


CHAPTER  XIV. 

COLORING    OF    METALS. 

METAL  coloring  and  bronzing  is  an  important  branch  of 
the  metal  industry,  its  object  being,  on  the  one  hand,  to  em- 
bellish the  original  metallic  surface  and,  on  the  other,  to 
protect  it  from  the  influence  of  atmospheric  air,  moisture, 
various  gases,  etc.  Although,  strictly  speaking,  these  opera- 
tions do  not  form  a  part  of  a  work  on  the  electro-deposition 
of  metals  and  cannot  be  adequately  treated  within  the  limits 
of  a  chapter,  a  few  methods  and  approved  formulas  will  here 
be  given  since  the  electro-plater  is  frequently  forced  to  make 
use  of  one  or  the  other  method  to  furnish  basis-metals  or 
electro-deposits  in  certain  shades  of  colors  demanded  by 
customers. 

Metal  coloring  may  be  effected  by  electrolytic,  chemical 
and  mechanical  means.  Methods  of  coloring  electrolytically 
have  been  given  under  Deposition  of  Nickel  (black  nickel- 
ling),  and  under  Deposition  of  Antimony  and  Arsenic. 

Mechanical  methods  of  coloring  require  the  use  of  pigments, 
bronze  powders,  varnishes,  etc.  and  cannot  be  here  fully  de- 
scribed. To  the  electro-plater  the  most  important  of  these 
operations  is  lacquering  which  will  be  described  in  the  next 
chapter. 

Attention  \yill  here  be  given  chiefly  to  coloring  metals  by 
chemical  means. 

The  practice  of  coloring  metals  requires  considerable  talent 
for  observation  and  a  certain  knowledge  of  the  behavior  of 
metals  or  metallic  alloys  towards  the  chemical  substances 
used. 

Especially  in  coloring  alloys,  for  instance,  brass,  their  per- 

(516) 


COLORING    OF    METALS.  517 

centage  composition  makes  a  difference,  and  patinas  can  be 
produced  upon  a  brass  richer  in  zinc,  which  cannot  be  ob- 
tained upon  an  alloy  richer  in  copper.  Hence  instructions 
for  patinizing  have  to  be  changed  in  one  or  the  other  direc- 
tion, and  this  problem  cannot  be  readily  solved  without  a 
certain  chemical  knowledge.  The  temperature  of  the  solu- 
tions used  is  also  of  great  importance,  and  the  directions  given 
in  this  respect  must  be  accurately  observed. 

1.  Coloring  copper. — With  the  use  of  chemicals  nearly  all 
-colors  can  be  produced  upon  copper,  as  well  as  upon  other 
metals  and  alloys,  by  first  coating  them  electrolytically  with 
copper  and  afterwards  coloring  the  deposit.  For  the  produc- 
tion of  yellow  and  brown,  alkaline  sulphides  are,  for  instance, 
used,  for  green,  copper  salts,  for  black,  metallic  silver,  bis- 
muth, platinum,  etc. 

All  shades  from  the  pale  red  of  copper  to  a  dark  chestnut 
brown  can  be  obtained  by  superficial  oxidation  of  the  copper. 
J^or  small  objects  it  suffices  to  heat  them  uniformly  over  an 
alcohol  flame.  With  larger  objects  a  more  uniform  result  is 
obtained  by  heating  them  in  oxidizing  fluids  or  brushing  them 
over  with  an  oxidizing  paste,  the  best  results  being  obtained 
with  a  paste  prepared,  according  to  the  darker  or  lighter  shades 
desired,  from  2  parts  of  ferric  oxide  and  1  part  of  black-lead, 
or  1  part  each  of  ferric  oxide  and  black-lead,  with  alcohol  or 
water.  Apply  the  paste  as  uniformly  as  possible  with  a 
brush,  and  place  the  object  in  a  warm  place  (oven  or  drying 
chamber).  The  darker  the  color  is  to  be  the  higher  the  tem- 
perature must  be,  and  the  longer  it  must  act  upon  the  object. 
When  sufficiently  heated,  the  dry  powder  is  removed  by  brush- 
ing with  a  soft  brush,  and  the  manipulation  repeated  if  the 
object  does  not  show  a  sufficiently  dark  tone.  Finally  the 
object  is  rubbed  with  a  soft  linen  rag  moistened  with  alcohol, 
or  brushed  with  a  soft  brush  and  a  few  drops  of  alcohol  until 
completely  dry,  and  then  with  a  brush  previously  rubbed 
upon  pure  wax.  The  more  or  less  dark  shade  produced  in 
this  manner  is  very  warm,  and  resists  the  action  of  the  air. 


518  ELECTRO-DEPOSITION    OF   METALS. 

Brown  color  on  copper. — Apply  to  the  thoroughly  cleansed 
object  a  paste  made  of  verdigris  3  parts,  ferric  oxide  3,  sal 
ammoniac  1,  and  sufficient  vinegar  and  heat  until  the  paste 
turns  black,  then  wash  and  dry  the  object.  By  the  addition 
of  some  blue  vitriol  to  the  paste  the  color  may  be  darkened  to 
chestnut-brown. 

A  brown  layer  of  cuprous  oxide  on  copper  is  produced  as  fol" 
lows:  After  polishing  the  articles  with  pumice  powder  apply 
with  a  brush  a  paste  made  of  verdigris  4  parts,  ferric  oxide  4, 
finely  rasped  horn  shavings  1,  and  a  small  quantity  of  vinegar. 
Dry,  heat  over  a  coal  fire,  wash,  and  smooth  with  the  polish- 
ing stone. 

A  brown  color  is  also  obtained  by  brushing  to  dry  ness  with 
a  hot  solution  of  1  part  of  potassium  nitrate,  1  of  common 
salt,  2  of  ammonium  chloride,  and  1  of  liquid  ammonia  in 
95  of  vinegar.  A  warmer  tone  is,  however,  produced  by  the 
method  introduced  in  the  Paris  Mint,  which  is  as  follows : 
Powder  and  mix  intimately  equal  parts  of  verdigris  and  sal 
ammoniac.  Take  a  heaping  tablespoonful  of  this  mixture 
and  boil  it  with  water  in  a  copper  kettle  for  about  twenty 
minutes,  and  then  pour  off  the  clear  fluid.  To  give  copper 
objects  a  bronze-like  color  with  this  fluid,  pour  part  of  it  into 
a  copper  pan  ;  place  the  objects  separately  in  it  upon  pieces 
of  wood  or  glass,  so  that  they  do  not  touch  each  other,  or  come 
in  contact  with  the  copper  pan,  and  then  boil  them  in  the 
liquid  for  a  quarter  of  an  hour.  Then  take  the  objects  from 
the  solution,  rub  them  dry  with  a  linen  cloth,  and  brush  them 
with  a  waxed  brush. 

A  beautiful  and  uniform  brown  tone  on  copper  is  produced  as 
follows :  Place  the  articles,  previously  freed  from  grease  and 
pickled,  in  a  solution  of  5J  ozs.  of  copper  sulphate,  and  2|  ozs. 
potassium  chloride  heated  to  140°  F.  until  the  desired  tone  is 
produced.  Then  brush  with  a  soft  brass-wire  brush,  rinse 
again  for  a  short  time  in  the  pickle,  and  finally  wipe  dry 
with  a  soft  cloth. 

Brown  of  various  shades  on  copper  is  produced  as  follows : 


COLORING    OF    METALS.  519 

Bring  the  objects  previously  cleansed  and  pickled  into  a  solu- 
tion of  liver  of  sulphur  1J  ozs.,  or  a  solution  of  trichloride  of 
antimony  (butter  of  antimony)  1J  ozs.  in  water  1  quart. 
When  the  desired  tone  is  produced,  rinse  the  objects  thor- 
oughly in  water  and  dry.  The  ^hade  of  the  color  may  be 
varied  by  the  concentration  of  the  bath  as  well  as  by  the 
length  of  time  of  its  action.  The  color  is  finally  fixed  by 
rubbing  with  a  rag  saturated  with  oil  varnish  or  by  rubbing 
heated  wax  upon  the  object. 

A  beautiful  brown  on  copper  by  the  so-called  Chinese  process 
is  produced  as  follows  :  Crystallized  verdigris  2  parts,  cinnabar 
2,  ammonium  chloride  5,  finely  powdered  alum  5,  intimately 
mixed  and  made  into  a  thin  paste  with  water  or  wine  vinegar. 
Apply  this  paste  with  a  brush  to  the  polished  surfaces.  Then 
heat  uniformly  over  a  coal  fire  and  when  cold  wash  carefully 
with  water.  By  the  addition  of  copper  sulphate  a  color  shad- 
ing more  into  chestnut-brown  is  obtained,  and  by  the  addition 
of  borax  one  shading  more  into  yellow. 

Gold-yellow  on  copper.  Treat  the  objects  with  a  hot  solution 
diluted  with  water,  of  mercury  10  parts  and  zinc  1  part  in 
hydrochloric  acid,  to  which  some  pulverized  tartar  has  been 
added. 

According  to  Manduit,  copper  and  coppered  articles  may 
be  bronzed  by  brushing  with  a  mixture  of  castor  oil  20  parts, 
alcohol  80,  soft  soap  40,  and  water  40.  This  mixture  pro- 
duces tones  from  bronze  Barbedienne  to  antique  green  patina, 
according  to  the  duration  of  the  action.  After  24  hours  the 
article  treated  shows  a  beautiful  bronze,  but  when  the  mixture 
is  allowed  to  act  for  a  greater  length  of  time  the  tone  is 
changed  and  several  different  shades  of  great  beauty  can  be 
obtained.  After  rinsing,  dry  in  hot  sawdust,  and  lacquer 
with  colorless  spirit  lacquer. 

Yellowish- brown  on  copper  is  produced  by  boiling  the  objects 
in  a  saturated  solution  of  potassium  chloride  and  ammonium 
nitrate.  By  heating  the  objects  after  drying  them,  a  more 
reddish-brown  color  is  obtained. 


520  ELECTRO-DEPOSITION    OF    METALS. 

Dark  brown  to  black  on  copper  is  obtained  by  dissolving 
nitrates  of  bismuth,  copper,  silver  or  cupriferous  silver  in 
water  and  adding  some  nitric  acid.  Copper  to  which  such  a 
fluid  has  been  applied  is,  when  heated,  colored  brown  with 
the  use  of  bismuth,  and  black  with  the  use  of  copper  and  sil- 
ver salts.  Very  dark  black  is -produced  by  placing  the  objects 
for  half  an  hour  over  a  vessel  containing  a  saturated  solution 
of  liver  of  sulphur  to  which  some  hydrochloric  acid  has  been 
added.  The  luster  may  be  increased  by  rubbing  with  a 
woolen  cloth  and  a  waxed  brush. 

Red  to  violet  shades  on  copper  articles.  According  to  a  pro- 
cess patented  in  Germany  by  M.  Mayer,  the  highly  polished 
copper  article  is  electrolytically  provided  with  a  thin  deposit 
of  arsenic  or  antimony.  For  the  preparation  of  the  bath,  solu- 
tion of  an  antimony  or  arsenic  salt  is  poured  into  a  ferric 
chloride  solution  till  the  precipitate  formed  redissolves.  A 
sheet  of  iron  may  serve  as  anode.  The  articles  thus  treated 
are  then  heated  to  cherry  red  and  again  polished.  It  is 
claimed  that  the  electro-deposit  as  a  carrier  of  oxygen  effects  a 
uniform  oxidation  of  the  copper  underneath,  but  at  the  same 
time  prevents  it  from  becoming  too  highly  oxidized  so  that 
by  heating  a  layer  of  oxide  is  chiefly  formed.  The  coating 
thus  obtained  shows  red  to  violet  shades,  adheres  firmly  and 
resists  physical  as  well  as  chemical  influences. 

Copper  is  colored  blue-black  by  dipping  the  object  in  a  hot 
solution  of  11 J  drachms  of  liver  of  sulphur  in  1  quart  of  water, 
moving  it  constantly.  Blue  gray  shades  are  obtained  with 
more  dilute  solutions.  It  is  difficult  to  give  definite  directions 
as  to  the  length  of  time  the  solution  should  be  allowed  to  act, 
since  this  depends  on  its  temperature  and  concentration. 
With  some  experience  the  correct  treatment,  however,  will 
soon  be  learned. 

The  so-called  cuivre-fume  is  produced  by  coloring  the  copper 
or  coppered  objects  blue-black  with  solution  of  liver  of  sulphur, 
then  rinsing,  and  finally  scratch-brushing  them,  whereby  the 
shade  becomes  somewhat  lighter.  From  raised  portions  which 


COLORING    OF    METALS.  521 

are  not  to  be  dark,  but  are  to  show  the  color  of  copper,  the 
coloration  is  removed  by  polishing  upon  a  felt  wheel  or  bob. 

Black  color  upon  copper  is  produced  by  a  heated  pickle  of  2 
parts  of  arsenious  acid,  4  of  concentrated  muriatic  acid,  1  of 
sulphuric  acid  of  66°  Be.,  and  24  of  water. 

Mat-black  on  copper. — Brush  the  object  over  with  a  solution 
of  1  part  of  platinum  chloride  in  5  of  water,  or  dip  it  in  the 
solution.  A  similar  result  is  obtained  by  dipping  the  copper 
object  in  a  solution -of  nitrate  of  copper  or  of  manganese,  and 
drying  over  a  coal  fire.  These  manipulations  are  to  be  re- 
peated until  the  formation  of  a  uniform  mat-black. 

A  solution  recommended  for  obtaining  a  deep  black  color  on 
copper  and  its  alloys  is  composed  as  follows :  Copper  nitrate 
100  parts,  water  100  parts.  The  copper  nitrate  is  dissolved  in 
the  water,  and  the  article,  if  large,  is  painted  with  it ;  if  small, 
it  may  be  immersed  in  the  solution.  It  is  then  heated  over  a 
clear  coal  fire  and  lightly  rubbed.  The  article  is  next  placed 
in,  or  painted,  with  a  solution  of  the  following  composition  : 
Potassium  sulphide  10  parts,  water  100,  hydrochloric  acid  5. 

More  uniform  results,  however,  are  obtained  by  using  a  solu- 
tion about  three  times  more  dilute  than  the  above,  viz.:  Cop- 
per nitrate  100  parts,  water  300.  Small  work  can  be  much 
more  conveniently  treated  by  immersion  in  the  solution,  and 
after  draining  off,  or  shaking  off  the  excess  of  the  solution, 
heating  the  work  on  a  hot  plate  until  the  copper  salt  is  de- 
composed into  the  black  copper  oxide.  It  would  be  difficult 
to  heat  large  articles  on  a  hot  plate,  but  a  closed  mufHe- 
furnace  would  give  better  results  than  an  open  coal  fire.  In 
any  case  heating  should  not  be  continued  longer  than  neces- 
sary to  produce  the  change  mentioned  above. 

Black  color  on  copper,  coppered  objects  and  alloys  rich  in 
copper.  For  this  purpose  Dr.  Groschuff  gives  the  following 
directions  :  Heat  a  suitable  quantity  of  5  per  cent,  soda  lye  in 
a  vessel  of  glass,  porcelain,  stoneware  or  enameled  iron  to 
212°  F.,  add  1  per  cent,  powdered  potassium  persulphate  and 
immerse  the  article  previously  secured  to  a  wire;  an  evolu- 


522  ELECTRO-DEPOSITION    OF    METALS. 

tion  of  oxygen  will  be  perceptible.  The  article  is  moved  to 
and  fro  in  the  hot  bath  till  the  black  color  desired  is  pro- 
duced which,  with  smaller  articles,  is  generally  the  case 
within  five  minutes.  Should  the  evolution  of  oxygen  cease 
previous  to  this,  add  1  per  cent,  more  of  potassium  persulphate. 

The  article  presenting  at  first  a  velvety  appearance  is  rinsed 
in  cold  water,  dried  with  a  soft  towel  and  rubbed  ;  it  will  then 
be  of  a  deep  black  color  with  mat  luster. 

The  solution  may  also  be  used  for  coloring  black  a  large 
number  of  alloys  with  a  high  percentage  of  copper.  Gen- 
erally speaking,  more  time  is  required  for  coloring  alloys 
than  copper. 

Patina.  This  term  is  applied  to  the  beautiful  green  colors 
antique  statues  and  other  art-works  of  bronze  have  acquired 
by  long  exposure  to  the  action  of  the  oxygen,  carbonic  acid, 
and  moisture  of  the  air,  whereby  a  thin  layer  of  copper  car- 
bonate is  formed  upon  them.  It  has  been  sought  to  accelerate 
by  chemical  means  the  formation  of  the  patina  thus  slowly 
produced  by  the  action  of  time  and  the  term  patinizing  has 
been  applied  to  the  production  of  such  colors. 

Artificial  patina.  There  are  numerous  directions  for  the 
production  of  an  artificial  patina  on  metallic  objects,  and,  in 
conformity  with  the  natural  principle  of  formation,  the  vari- 
ous artificial  processes  are  based  upon'  the  slowest  possible 
action  of  the  patinizing  fluid. 

To  avoid  stains  the  surfaces  of  the  metallic  objects  should 
be  as  bright  as  possible,  and  any  adhering  grease  must  first 
be  removed  by  washing  with  dilute  soda  lye.  The  objects  are 
then  placed,  without  touching  them  with  the  bare  hands,  on 
the  bench  or  other  place  where  they  are  to  be  patinized. 

Patinizing  is  rfected  with  a  dilute  solution  applied  with  a 
brush  or  sponge.  After  allowing  the  first  application  to  dry 
at  a  temperature  of  about  60°  F.,  the  process  is  several  times 
repeated.  The  composition  of  the  metal  to  which  the  patiniz- 
ing fluid  is  to  be  applied,  exerts  an  influence  upon  the  forma- 
tion of  a  patina  of  good  quality,  the  latter  being  most  readily 


COLORING    OF    METALS.  523 

formed  upon  bronze,  while  copper  and  brass  are  more  difficult 
to  patinize  ;  alloys  containing  arsenic  easily  turn  black. 

Donath  makes  a  distinction  between  acid  and  alkaline  pat- 
inizing  fluids.  The  former  contain  acetic  acid,  oxalic  acid, 
hydrofluo-silicic  acid,  and  the  latter,  ammonia,  ammonium 
carbonate,  etc.  Coatings  effected  with  acids  require  a  longer 
time  for  their  formation  ;  they  are  in  the  beginning  less  crys- 
talline and  at  first  blue-green,  later  on,  of  the  color  of  ver- 
digris, but  possess  less  resistance  towards  water.  Coatings 
produced  with  ammoniacal  fluids  have  a  dull,  earthy  appear- 
ance, and  a  blue-green  to  gray-green  color.  Yellow-green 
tones  are  obtained  by  the  addition  of  chlorides — common  salt, 
sal  ammoniac — to  the  solution,  while  copper  nitrate  or  copper 
acetate  yield  more  blue-green  colorations.  If  a  yellow-green 
coloration  is  to  be  changed  into  blue-green,  only  ammonium 
carbonate  solution  can  subsequently  be  used. 

Imitation  of  genuine  green  patina,  as  well  as  its  rapid  forma- 
tion upon  objects  of  copper,  and  of  bronze  and  brass,  is  ob- 
tained by  repeatedly  brushing  the  objects  with  solution  of 
ammonium  chloride  in  vinegar,  the  action  of  the  solution 
being  accelerated  by  the  addition  of  verdigris.  A  solution  of 
9  drachms  of  ammonium  chloride  and  2J  drachms  of  potas- 
sium binoxalate  (salt  of  sorrel)  in  1  quart  of  vinegar  acts  still 
better.  When  the  first  coating  is  dry,  wash  the  object,  and 
repeat  the  manipulations,  drying  and  washing  after  each  ap- 
plication, until  a  green  patina  is  formed.  It  is  best  to  bring 
the  articles  after  being  brushed  over  with  the  solution  into  a 
hermetically  closed  box,  upon  the  bottom  of  which  a  few 
shallow  dishes  containing  very  dilute  sulphuric  or  acetic  acid 
and  a  few  pieces  of  marble  are  placed.  Carbonic  acid  being 
thereby  evolved,  and  the  air  in  the  box  being  kept  sufficiently 
moist  by  the  evaporation  of  water,  the  conditions  required  for 
the  formation  of  genuine  patina  are  thus  fulfilled.  If  the 
patina  is  to  show  a  more  bluish  tone,  bfush  the  objects  with  a 
solution  of  4J  ozs.  of  ammonium  carbonate  and  1 J  ozs.  of  am- 
monium chloride  in  1  quart  of  water,  to  which  a  small  quan- 
tity of  gum  tragacanth  may  be  added. 


524  ELECTRO-DEPOSITION    OF    METALS. 

A  blue-green  patina,  much  used  in  Paris,  is  produced  by 
heating  in  the  following  solution  :  Water  500  grammes,  cor- 
rosive sublimate  2.5  grammes,  saltpetre  8.6  grammes,  borax 
5.6  grammes,  zinc  oxide  11.3  grammes,  copper  nitrate  22  to 
22.5  grammes. 

A  brown  patina  is  obtained  with  the  following  solution  : 
Oxalic  acid  3  grammes,  sal  ammoniac  15  grammes,  distilled 
water  280  grammes. 

The  article  is  to  be  frequently  brushed  with  the  solution  ; 
this  process  requires  considerable  time. 

Patina  for  copper  and  brass.  The  production  of  two  fine 
tones  of  color  upon  copper  and  brass  articles  is  due  to  the  fact 
that  ammonia  attacks  and  eventually  dissolves  copper.  The 
following  directions  are  given-  by  La  Nature :  If  to  objects  of 
copper  is  to  be  given  the  appearance  of  very  antique  art 
objects  recently  dug  up,  it  is  only  necessary  to  immerse  them 
in  ammonia.  The  effect  does  not  show  itself  immediately, 
but  only  after  24  hours.  A  beautiful  dark  green  coating, 
which  adheres  quite  firmly,  is  formed.  By  allowing  the 
copper  object  to  remain  for  several  days  in  the  fluid  the  sur- 
face is  more  strongly  attacked  and  the  antique  effect  is 
heightened. 

Another  kind  of  patina  which  cannot  be  produced  upon 
copper  but  only  upon  brass  is  obtained  by  immersing  the 
object  in  a  hot,  nearly  boiling,  mixture  of  75  cubic  centimeters 
of  ammonia,  the  same  quantity  of  water  and  10  grammes  of 
potash.  A  uniform  durable  patina  shows  itself  in  half  a 
minute.  By  allowing  the  article  to  remain  longer  in  the  solu- 
tion the  patina  acquires,  without  being  materially  altered,  a 
steely  bluish-gray  luster. 

To  produce  a  steel-gray  color  upon  copper,  immerse  the  clean 
and  pickled  objects  in  a  heated  solution  of  chloride  of  anti- 
mony* in  hydrochloric  acid.  By  using  a  strong  electric  cur- 
rent the  objects  may  also  be  coated  with  a  steel-gray  deposit  of 
arsenic  in  a  heated  arsenic  bath. 

For  coloring  copper  dark  steel-gray,  a  pickle  consisting  of  1 


COLORING    OF    METALS.  525 

quart  of  hydrochloric  acid,  0.125  quart  of  nitric  acid,  1J  ozs. 
of  arsenious  acid,  and  a  like  quantity  of  iron  filings  is  recom- 
mended. 

Various  colors  upon  massive  copper. — First  draw  the  object 
through  a  pickle  composed  of  sulphuric  acid  60  parts,  hydro- 
chloric acid  24.5,  and  lampblack  15.5  ;  or  of  nitric  acid  100 
parts,  hydrochloric  acid  1 J  and  lampblack  J.  Then  dissolve 
in  a  quart  of  water,  4J  ozs.  of  sodium  hyposulphite,  and  in 
another  quart  of  water,  14J  drachms  of  blue  vitriol,  5J 
drachms  of  crystallized  verdigris,  and  7}  grains  of  sodium 
arsenate.  Mix  equal  volumes  of  the  two  solutions,  but  no 
more  than  is  actually  necessary  for  the  work  in  hand,  and 
heat  to  between  167°  and  176°  F.  By  dipping  articles  of 
copper,  brass,  or  nickel  in  the  hot  solution  they  become  im- 
mediately colored  with  the  colors  mentioned  below,  one  color 
passing  within  a  few  seconds  into  the  other,  and  for  this 
reason  the  effect  must  be  constantly  controlled  by  frequently 
taking  the  objects  from  the  bath.  The  colors  successively 
formed  are  as  follows  : 

Upon  copper  :                    Upon  brass  :  Upon  nickel : 

Orange,  Golden-yellow,  Yellow, 

Terra-cotta.  Lemon  color,  Blue, 

Red  (pale),  Orange,  Iridescent. 

Blood-red,  Terra-cotta, 

Iridescent.  Olive-green. 

Some  of  these  colors  not  being  very  durable,  have  to  be 
protected  by  a  coat  of  lacquer  or  paraffine.  It  is  further 
necessary  to  diligently  move  the  objects,  so  that  all  portions 
acquire  the  same  color.  The  bath  decomposes  rapidly,  and 
hence  only  sufficient  for  2  or  3  hours'  use  should  be  mixed  at 
one  time. 

2.  Coloring  brass  and  bronzes.  Most  of  the  directions  given 
for  coloring  copper  are  also  available  for  brass  and  bronzes, 
especially  those  for  the  production  of  patinas  and  the  oxidized 
tones  by  a  mixture  of  ferric  oxide  and  blacklead. 


526  ELECTRO-DEPOSITION    OF    METALS. 

Many  colorations  on  brass  are,  however,  effected  only  with 
difficulty,  and  are  partially  or  entirely  unsuccessful  as,  for 
instance,  coloring  black  with  liver  of  sulphur.  As  a  pickle 
for  the  production  of  a 

Lustrous  black  on  brass,  the  following  solutions  may  be  used  : 
Dissolve  freshly  precipitated  carbonate  of  copper,  while  still 
moist,  in  strong  liquid  ammonia,  using  sufficient  of  the  cop- 
per salts  so  that  a  small  excess  remains  undissolved,  or,  in 
other  words,  that  the  ammonia  is  saturated  with  copper.  The 
carbonate  of  copper  is  prepared  by  mixing  hot  solutions  of 
equal  parts  of  blue  vitriol  and  of  soda,  filtering  off  and  wash- 
ing the  precipitate. 

Dilute  the  solution  of  the  copper  salt  in  ammonia  with  one- 
fourth  its  volume  of  water,  add  31  to  46  grains  of  graphite 
and  heat  to  between  95°  and  104°  F. 

According  to  experiments  in  the  laboratory  of  the  Physikal- 
isch-Technischen  Reichsanstalt,  the  following  proportions  have 
proved  very  effective  :  Copper  carbonate  3J  ozs.,  liquid  am- 
monia 26  J  ozs.,  and  an.  addition  of  5}  ozs.  of  water.  Place 
the  clean  and  pickled  articles  in  this  pickle  until  they  show  a 
full  black  tone,  then  rinse  in  water,  immerse  in  hot  water, 
and  dry  in  sawdust.  The  solution  soon  spoils,  and  hence  no 
more  than  required  for  immediate  use  should  be  prepared. 

For  black  pickling  in  the  hot  way,  a  solution  of  21  ozs.  of 
copper  nitrate  in  7  ozs.  of  water  mixed  with  a  solution  of  3} 
grains  of  silver  nitrate  in  J  oz.  of  water,  is  recommended. 

Black  of  a  beautiful  luster  may  be  produced,  especially  upon 
nickeled  brass,  by  suspending  the  objects  as  anodes  in  a  solu- 
tion of  lead  acetate  (sugar  of  lead)  in  caustic  soda,  using  a 
slight  current-density. 

Black  color  on  brass  optical  instruments  is  produced  by  plac- 
ing the  brass  in  a  solution  of  platinum  or  chloride  of  gold 
mixed  with  stannous  nitrate.  The  Japanese  bronze  brass  with 
a  solution  of  copper  sulphate,  alum  and  verdigris.  Success  in 
bronzing  depends  on  the  temperature  of  the  alloy,  the  propor- 
tions of  metals  used  in  the  alloy,  drying,  and  many  other 


COLORING    OF    METALS.  527 

small  details  which  can  be  learned  only  by  practical  experi- 
ence. 

Steel  gray  on  brass. — Use  a  mixture  of  1  Ib.  of  strong  hydro- 
chloric acid  with  1  pint  of  water  to  which  are  added  5J  ozs.  of 
iron  filings  and  a  like  quantity  of  pulverized  antimony  sulphide. 

Hydrochloric  acid  compounded  with  white  arsenic  is  also 
recommended  for  the  purpose.  The  mixture  is  brought  into 
a  lead  vessel,  and  the  object  dipped  in  it  should  be  in  contact 
with  the  lead  of  the  vessel,  or  be  wrapped  around  with  a  strip 
of  lead. 

Solution  of  antimony  chloride  produces  a  gray  color  with  a 
bluish  tinge,  and  a  hot  solution  of  arsenious  chloride  in  a 
small  quantity  of  water  a  steel  gray  color. 

Silver  color  on  brass.  Dissolve  in  a  well-glazed  vessel  1J 
ozs.  cream  of  tartar  and  \  oz.  of  tartar  emetic  in  1  quart  of 
hot  water,  and  add  to  the  solution  If  ozs.  of  hydrochloric 
acid,  4J  ozs.  of  granulated,  or  better,  pulverized  tin  and  1  oz. 
of  powdered  antimony.  Heat  the  mixture  to  boiling  and  im- 
merse the  articles  to  be  colored.  After  boiling  at  the  utmost 
for  half  an  hour,  the  articles  will  be  provided  with  a  beautiful, 
hard  and  durable  coating. 

Pale  gold  color  on  brass.  Dissolve  in  90  parts  by  weight  of 
water,  3.6  parts  by  weight  of  caustic  soda,  and  the  same 
quantity  of  milk  sugar.  Boil  the  solution  J  hour.  Then  add 
a  solution  of  3.6  parts  by  weight  in  10  parts  by  weight  of  hot 
water.  Use  the  bath  at  a  temperature  of  176°  F. 

Straw  color,  to  brown,  through  golden  yellow,  and  tombac  color 
on  brass  may  be  obtained  with  solution  of  carbonate  of  copper 
in  caustic  soda  lye.  Dissolve  5.25  ozs.  of  caustic  soda  in  1 
quart  of  water,  and  add  1  j  ozs.  of  carbonate  of  copper.  By 
using  the  solution  cold,  a  dark,  golden-yellow  is  first  formed, 
which  finally  passes  through  pale  brown  into  dark  brown  with 
a  green  luster.  Coloration  is  more  rapidly  effected  by  using 
the  solution  hot. 

Color  resembling  gold  on  brass,  according  to  Dr.  Kayser : 
Dissolve  8J  drachms  of  sodium  hyposulphite  in  17  drachms 


528  ELECTRO-DEPOSITION    OF    METALS. 

of  water,  and  add  5.64  drachms  of  solution  of  antimonious 
chloride  (butter  of  antimony).  Heat  the  mixture  to  boiling 
for  some  time,  then  filter  off  the  red  precipitate  formed,  and 
after  washing  it  several  times  upon  the  filter  with  vinegar, 
suspend  it  in  2  or  3  quarts  of  hot  water ;  then  heat  and  add 
concentrated  soda  lye  until  solution  is  complete.  In  this  hot 
solution  dip  the  clean  and  pickled  brass  objects,  removing 
them  frequently  to  see  whether  they  have  acquired  the  desired 
coloration.  By  remaining  too  long  in  the  bath,  the  articles 
become  gray. 

Brown  color,  called  bronze  Barbedienne,  on  brass.  This  beau- 
tiful color  may  be  produced  as  follows  :  Dissolve  by  vigorous 
shaking  in  a  bottle,  freshly  prepared  arsenious  sulphide  in 
liquid  ammonia,  and  compound  the  solution  with  antimonious 
sulphide  (butter  of  antimony)  until  a  slight  permanent  tur- 
bidity shows  itself,  and  the  fluid  has  acquired  a  deep  yellow 
color.  Heat  the  solution  to  95°  F.,  and  suspend  the  brass 
objects  in  it.  They  become  at  first  golden-yellow  and  then 
brown,  but  as  they  come  from  the  bath  with  a  dark  dirty 
tone,  they  have  to  be  several  times  scratch-brushed  to  bring 
out  the  color.  If,  after  using  it  several  times,  the  solution 
fails  to  work  satisfactorily,  add  some  antimonious  sulphide. 
The  solution  decomposes  rapidly,  and  should  be  prepared 
fresh  every  time  it  is  to  be  used. 

A  suitable  solution  may  also  be  prepared  by  boiling  0.88 
oz.  of  arsenious  acid  and  1  oz.  of  potash  in  1  pint  of  water 
until  the  acid  is  dissolved  and,  when  cold,  add  250  cubic 
centimeters  of  ammonium  sulphide.  According  to  the  degree 
of  dilution,  brown  to  yellow  tones  are  obtained. 

By  this  method  only  massive  brass  objects  can  be  colored 
brown.  To  brassed  zinc  and  iron-,  the  solution  imparts  brown- 
black  tones,  which,  however,  are  also  quite  beautiful. 

Upon  massive  brass,  as  well  as  upon  brassed  zinc  and  iron 
objects,  bronze  Barbedienne  may  be  produced  as  follows  :  Mix 
3  parts  of  red  sulphide  of  antimony  (stibium  sulfuralum  auran- 
tianum)  with  1  part  of  finely  pulverized  bloodstone,  and  tritu- 


COLORING    OF    METALS.  529 

rate  the  mixture  with  ammonium  sulphide  to  a  not  too  thickly- 
fluid  pigment.  Apply  this  pigment  to  the  objects  with  a  brush, 
and,  after  allowing  to  dry  in  a  drying-chamber,  remove  the 
powder  by  brushing  with  a  soft  brush. 

In  Paris  bronze  articles  are  colored  dead-yellow  or  clay-yellow 
to  dark  brown  by  first  brushing  the  pickled  and  thoroughly 
rinsed  objects  with  dilute  ammonium  sulphide,  and,  after  dry- 
ing, removing  the  coating  of  separated  sulphur  by  brushing. 
Dilute  solution  of  sulphide  of  arsenic  in  ammonium  is  then  ap- 
plied, the  result  being  a  color  resembling  mosaic  gold.  The 
more  frequently  the  arsenic  solution  is  applied,  the  browner 
the  color  becomes.  By  substituting  for  the  arsenic  solution  one 
of  sulphide  of  antimony  in  ammonia  or  ammonium  sulphide, 
colorations  of  a  more  reddish  tone  are  obtained. 

Dead  red  color  on  brass.  Suspend  the  articles,  previously 
thoroughly  freed  from  grease,  in  a  solution  of  equal  parts  of 
potassium-lead  oxide  and  red  prussiate  of  potash  heated  to 
122°  F.  until  they  have  acquired  a  sufficiently  dark  color. 

For  coloring  brass  articles  in  large  quantities  brown  by  boiling, 
the  following  solution  is  recommended  :  Water  1  quart,  potas- 
sium chromate  1J  ozs.,  nickel  sulphate  1J  ozs.,  potassium 
permanganate  4f  drachms. 

Solution  of  blue  vitriol  and  potassium  permanganate  serves 
the  same  purpose.  However,  after  boiling,  the  articles  must 
not  be  scratch-brushed,  but  after  drying  rubbed  with  vaseline. 

Violet  and  cornflower-blue  upon  brass:  Dissolve  in  1  quart  of 
water  4J  ozs.  of  sodium  hyposulphite,  and  in  another  quart  of 
water  1  oz.  3|  drachms  of  crystallized  lead  acetate  (sugar  of 
lead),  and  mix  the  solutions.  Heat  the  mixture  to  176°  F., 
and  then  immerse  the  cleansed  and  pickled  articles,  moving 
them  constantly.  First  a  gold-yellow  coloration  appears, 
which,  however,  soon  passes  into  violet  and  blue,  and  if  the 
bath  be  allowed  to  act  further,  into  green.  The  action  is 
based  upon  the  fact  that  in  an  excess  of  hyposulphite  of  soda, 
solution  of  hyposulphite  of  lead  is  formed,  which  decomposes 
slowly  and  separates  sulphide  of  lead,  which  precipitates  upon 
34 


530  ELECTRO-DEPOSITION    OF    METALS. 

the  brass  objects,  and,  according  to  the  thickness  of  the 
deposit,  produces  the  various  lustrous  colors. 

Upon  the  same  action  is  based  the  spurious  gilding  of  small 
silvered  brass  and  tombac  articles.  Though  this  process  has 
been  known  for  many  years,  Joseph  Dittrich  obtained  a  Ger- 
man patent  for  it.  He  dissolves  in  6J  Ibs.  of  water,  10J  ozs. 
of  sodium  hyposulphite,  and  3J  ozs.  of  lead  acetate  (sugar  of 
lead). 

Similar  lustrous  colors  are  obtained  by  dissolving  2.11  ozs. 
of  pulverized  tartar  in  1  quart  of  water,  and  1  oz.  of  chloride 
of  tin  in  J  pint  of  water,  mixing  the  solution,  heating,  and 
pouring  the  clear  mixture  into  a  solution  of  6.34  ozs.  of  sodium 
hyposulphite  in  1  pint  of  water.  Heat  this  mixture  to  176° 
F.,  and  immerse  the  pickled  brass  objects. 

Ebermayer's  experiments  in  coloring  brass. — Below  the  results 
of  Ebermayer's  experiments  are  given.  In  testing  the  direc- 
tions, the  same  results  as  those  claimed  by  Ebermayer  were 
not  always  obtained  ;  and  variations  are  given  in  parentheses. 

I.  Blue  vitriol  8  parts  by  weight,  crystallized  ammonium 
chloride  2,  water  100,  give  by  boiling  a  greenish  color.     (The 
color  is  olive-green,  and  useful  for  many  purposes.     The  color- 
ation, however,  succeeds  only  upon  massive  brass,  but  not 
upon  brassed  zinc.) 

II.  Potassium  chlorate  10  parts  by  weight,  blue  vitriol  10, 
water  1000,  give  by  boiling  a  brown-orange  to  cinnamon-brown 
color.     (Only  a  yellow-orange  color  could  be  obtained.) 

III.  By  dissolving  8  parts  by  weight  of  blue  vitriol  in  1000 
of  water,  and  adding  100  of  caustic  soda  until  a  precipitate  is 
formed,  atid  boiling  the  objects  in  the  solution,  a  gray -brown 
color  is  obtained,  which  can  be  made  darker  by  the  addition 
of  colcothar.     (Stains  are  readily  formed.     Brassed   zinc  ac- 
quires a  pleasant  pale-brown.) 

IV.  With  50  parts  by  weight  of  caustic  soda,  50  of  sulphide 
of  antimony,  and  500  of  water,  a  pale  fig-brown  color  is  pro- 
duced.    (Fig-brown  could  not  be  obtained,  the  shade  being 
rather  dark  olive-green.) 


COLORING    OF    METALS.  531 

V.  By  boiling  400  parts  by  weight  of  water,  25  of  sulphide 
of  antimony  and  600  of  calcined  soda,  and  filtering  the  hot 
solution,  mineral  kermes  is  precipitated.     By  taking  of  this  5 
parts  by  weight  and  heating  with  5  of  tartar,  400  of  water, 
and   10  of  sodium   hyposulphite,  a  beautiful  steel-gray  is  ob- 
tained.    (The  result  is  tolerably  sure  and  good.) 

VI.  Water  400  parts  by  weight,   potassium  chlorate  20, 
nickel  sulphide  10,  give,  after  boiling  for  some  time,  a  brown 
color,  which,  however,  is  not   formed   if  the  sheet  has  been 
pickled.     (The  brown  color  obtained  is  not  very  pronounced.) 

VII.  Water  250  parts  by  weight,  potassium  chlorate  5,  car- 
bonate of  nickel  2,  and  sulphate  of  ammonium  and  nickel  5, 
give,  after  boiling  for  some  time,  a  brown-yellow  color,  playing 
into  a  magnificent  red.     (The  results  obtained  were  only  in- 
different.) 

VIII.  Water  250   parts  by  weight,  potassium   chlorate  5, 
and  sulphate  of  nickel  and  ammonium   10,  give  a  beautiful 
dark  brown.     Upon  massive  brass  a  good  dark  brown  is  ob- 
tained.    The*  formula,  however,  is  not  available  for  brassed 
zinc. 

3.  Coloring  zinc.  Direct  coloring  of  zinc  does  not  give,  as  a 
rule,  reliable  results,  and  it  is  therefore  recommended  to  first 
copper  or  tin  the  zinc  and  color  the  coating  thus  obtained. 

Black  on  zinc.  a.  Dissolve  crystallized  copper  nitrate  2 
parts  and  copper  chloride  2  parts  in  acidulated  water  64  parts, 
and  add  to  the  solution  hydrochloric  acid  of  1.1  specific  gravity 
8  parts.  The  resulting  fluid  has  a  slightly  bluish  color.  A 
sheet  of  zinc,  previously  scoured  bright  by  means  of  dilute 
hydrochloric  acid  and  fine  sand,  will,  when  immersed  in  the 
fluid,  immediately  be  colored  intensely  black.  By  removing 
the  sheet  thus  treated,  at  once  from  the  fluid  and  rinsing  it 
without  loss  of  time  in  a  large  quantity  of  pure  water  and 
allowing  it  to  dry,  the  black  coating  will  adhere  very  firmly 
to  the  zinc. 

b.  Dip  the  object  in  a  boiling  solution  of  pure  green  vitriol 
5.64  ozs.  and  ammonium  chloride  3.17  ozs.  in  2J  quarts  of 


532  ELECTRO-DEPOSITION    OF    METALS. 

water.  Remove  the  loose  black  precipitate  deposited  upon 
the  object  by  brushing,  again  dip  the  object  in  the  hot  solu- 
tion and  then  hold  it  over  a  coal  fire  until  the  ammonium 
chloride  evaporates.  By  repeating  the  operation  three  or  four 
times,  a  firmly  adhering  black  coating  is  formed. 

Gray,  yellow,  brown  to  black  colors  upon  zinc. — Bring  the 
articles  into  a  bath  which  contains  6  to  8  quarts  of  water, 
3J  ozs.  of  nickel-ammonium  sulphate,  3J  ozs.  of  blue  vitriol 
and  3J  ozs.  of  potassium  chlorate.  The  bath  is  to  be  heated 
to  140°  F.  By  increasing  the  content  of  blue  vitriol  a  dark 
color  is  obtained,  and  a  brighter  one  with  the  use  of  a  larger 
proportion  of  nickel  salt.  The  correct  proportions  for  the  de- 
termined shades  will  soon  be  learned  by  practice.  When 
colored,  the  articles  are  thoroughly  rinsed,  dried,  without  rub- 
bing, in  warm  sawdust,  and  finally  rubbed  with  a  flannel  rag 
moistened  with  linseed  oil,  whereby  they  acquire  deep  luster, 
and  the  coating  becomes  more  durable. 

Brown  patina  on  zinc. — The  objects  are  first  coppered  in  a 
copper  bath  containing  potassium  cyanide,  then  in  the  acid- 
copper  bath,  rinsed,  and  finally  suspended  in  a  pickle  consist- 
ing of  a  solution  of  5.29  ozs.  of  blue  vitriol  and  2.82  ozs.  of 
potassium  chlorate  in  one  quart  of  water  at  140°  F.,  until  they 
show  the  desired  brown  tone.  They  are  then  rinsed  in  water, 
scratch-brushed  with  a  fine  brass-brush,  for  a  short  time  re- 
placed in  the  pickle,  again  thoroughly  rinsed  in  water,  and 
dried  with  a  soft  cloth. 

By  suspending  zinc  in  a  nickel  bath  slightly  acidulated  with 
sulphuric  acid,  a  firmly  adhering  blue-black  coating  is,  after 
some  time,  formed  without  the  use  of  a  current.  This  coating 
is  useful  for  many  purposes.  A  similar  result  is  obtained  by 
immersing  the  zinc  objects  in  a  solution  of  2.11  ozs.  of  the 
double  sulphate  of  nickel  and  ammonium  and  a  like  quantity 
of  crystallized  ammonium  chloride  in  1  quart  of  water.  The 
articles  become  first  dark  yellow,  then  successively  brown, 
purple-violet  and  indigo-blue,  and  stand  slight  scratch-brushing 
and  polishing. 


COLORING    OF    METALS.  533 

A  gray  coating  on  zinc  is  obtained  by  a  deposit  of  arsenic  in 
a  heated  bath  composed  of  2.82  ozs.  of  arsenious  acid,  8.46 
drachms  of  sodium  pyrophosphate  and  If  drachms  of  98  per 
cent,  potassium  cyanide,  and  1  quart  of  water.  A  strong  cur- 
rent should  be  used  so  that  a  vigorous  evolution  of  hydrogen 
is  perceptible.  Platinum  sheets  or  carbon  plates  are  used  as 
anodes. 

A  sort  of  bronzing  on  zinc  is  obtained  by  rubbing  it  with  a 
paste  of  pipe-clay  to  which  has  been  added  a  solution  of  1 
part  by  weight  of  crystallized  verdigris,  1  of  tartar,  and  2  of 
crystallized  soda. 

Red-brown  shades  on  zinc.  Rub  with  solution  of  copper 
chloride  in  ammonia. 

Yellow-brown  shades  on  zinc.  Rub  with  solution  of  copper 
chloride  in  vinegar. 

4.  Coloring  iron.  Browning  of  gun  barrels.  Apply  a  mix- 
ture of  equal  parts  of  butter  of  antimony  and  olive  oil.  Allow 
the  mixture  to  act  for  12  to  14  hours,  then  remove  the  excess 
with  a  woolen  rag  and  repeat  the  application.  When  the 
second  application  has  acted  for  12  to  24  hours,  the  iron  or 
steel  will  be  coated  with  a  bronze-colored  layer  of  ferric  oxide 
with  antimony,  which  resists  the  action  of  the  air,  and  may 
be  made  lustrous  by  brushing  with  a  waxed  brush. 

A  patina  which  protects  metals — iron,  zinc,  tin,  etc. — from 
rust,  is,  according  to  Haswell,  obtained  as  follows  :  The  article, 
previously  freed  from  grease  and  pickled,  is  suspended  as 
negative  electrode  in  a  solution  of  15J  grains  of  ammonium 
molybdate  and  J  oz.  of  ammonium  nitrate  in  1  quart  of  water. 
A  weak  current  should  be  used — 0.2  to  0.3  ampere  per  15J 
square  inches. 

To  protect  gun  barrels  and  other  articles  of  iron  and  steel 
from  rust,  they  are,  according  to  Haswell,  suspended  as  anodes 
in  a  bath  consisting  of  a  solution  of  lead  nitrate  and  sodium 
nitrate,  into  which  manganous  oxide  has  been  stirred. 

Lustrous  black  on  iron.  Apply  solution  of  sulphur  in  tur- 
pentine prepared  by  boiling  on  the  water-bath.  After  the 


534  ELECTRO-DEPOSITION    OF    METALS. 

evaporation  of  the  turpentine  a  thin  layer  of  sulphur  remains 
upon  the  iron,  which  on  heating  immediately  combines  with 
the  metal. 

A  lustrous  black  is  also  obtained  by  freeing  the  iron  articles 
from  grease,  pickling,  and  after  drying,  coating  with  sulphur 
balsam,*  and  burning  in  at  a  dark-red  heat.  If  pickling  is 
omitted,  coating  with  sulphur  balsam  and  burning-in  must  be 
twice  or  three  times  repeated. 

The  same  effect  is  produced  by  applying  a  mixture  of  three 
parts  flowers  of  sulphur,  and  1  part  graphite  with  turpentine, 
and  heating  in  the  muffle. 

According  to  Meritens  a  bright  black  color  can  be  obtained 
on  iron  by  making  it  the  anode  in  distilled  water,  kept  at  158° 
F.,  and  using  an  iron  plate  as  cathode.  The  method  was 
tested  as  follows  :  A  piece  of  bright  sheet  pen-steel  was  placed 
in  distilled  water  and  made  the  anode  by  connecting  it  with  the 
positive  pole  of  a  plating  dynamo,  and  a  similar  sheet  was  con- 
nected with  the  negative  pole  to  form  the  cathode.  An  electro- 
motive force  of  8  volts  was  employed.  After  some  time  a  dark 
stain  was  produced,  but  it  lacked  uniformity.  The  experi- 
ment was  repeated  with  larger  plates,  when  a  good  blue-black 
color  was  obtained  on  the  anode  in  half  a  hour.  On  drying 
in  sawdust  the  color  appeared  less  dense,  and  inclined  to  a 
dark  straw  tint.  The  back  of  the  plate  was  also  colored,  but 
not  regularly.  The  face  of  the  cathode  was  discolored  with  a 
grayish  stain  on  the  side  opposite  to  the  anode,  but  on  the 
other  side  the  appearance  was  almost  identical  with  the  black 
of  the  anode.  The  water  became  of  a  yellowish  color. 

Fresh  distilled  water  was  then  boiled  for  a  long  time  so  as 
to  expel  all  trace  of  oxygen  absorbed  from  the  atmosphere, 
and  the  experiment  repeated  as  in  the  former  cases.  No  per- 
ceptible change  took  place  after  the  connection  had  been  made 
with  the  dynamo  for  a  quarter  of  an  hour.  After  the  inter- 
val of  one  hour  a  slight  darkening  occurred,  but  the  effect 

*  Sulphur  dissolved  in  linseed  oil. 


COLORING    OF    METALS.  535 

was  much  less  than  that  produced  in  five  minutes  in  aerated 
water. 

The  action  of  the  liquid  in  coloring  the  steel  is  evidently  one 
of  oxidation,  due  to  the  dissolved  oxygen,  which  becomes  more 
chemically  active  under  the  influence  of  the  electric  condition, 
and  gradually  unites  with  the  iron. 

The  mat  black  coating  upon  clock  cases  of  iron  and  steel — the 
so-called  Swiss  mat — is  not  produced  by  the  electric  process, 
but  by  a  slow  process  of  oxidation,  ferroso-ferric  oxide  being 
formed.  The  objects,  previously  cleaned  from  grease  with  the 
greatest  care,  are  brushed  over  by  means  of  a  sponge  or  brush 
with  a  ferric  chloride  solution,  called  ferroxydin,  allowed  to 
dry,  and  then  steamed.  For  the  production  of  a  very  strong 
mat,  the  process  is  to  be  twice  or  three  times  repeated.  By 
one  operation  a  beautiful  black  with  semi-luster  is  obtained. 

Blue  color  on  iron  and  steel.  Immerse  the  article  in  J  per 
cent,  solution  of  red  prussiate  of  potash  mixed  with  an  equal 
volume  of  J  per  cent,  solution  of  ferric  chloride. 

Brown-black  coating  with9  bronze  luster  on  iron.  Heat  the 
bright  objects  and  brush  them  over  with  saturated  potassium 
dichromate  solution.  When  dry,  heat  them  over  a  charcoal 
fire,  and  wash  until  the  water  running  off  shows  no  longer  a 
yellow  color.  Repeat  the  operation  twice  or  three  times.  A 
similar  coating  is  obtained  by  heating  the  iron  objects  with  a 
solution  of  10  parts  by  weight  of  green  vitriol  and  1  part  of 
sal  ammoniac  in  water. 

To  give  iron  a  silvery  appearance  with  high  luster. — Scour  the 
polished  and  pickled  iron  objects  with  a  solution  prepared  as 
follows:  Heat  moderately  1J  ozs.  of  chloride  of  antimony,  0.35 
ozs.  of  pulverized  arsenious  acid,  2.82  ozs.  of  elutriated  blood- 
stone with  1  quart  of  90  per  cent,  alcohol  upon  a  water-bath 
for  half  an  hour.  Partial  solution  takes  place.  Dip  into  this 
fluid  a  tuft  of  cotton  and  go  over  the  iron  portions,  using  slight 
pressure.  A  thin  film  of  arsenic  and  antimony  is  thereby  de- 
posited, which  is  the  more  lustrous  the  more  carefully  the  iron 
has  previously  been  polished. 


536  ELECTRO-DEPOSITION    OF    METALS. 

5.  Coloring  of  tin. — A  bronze-like  patina  on  tin  may  be  ob- 
tained by  brushing  the  object  with  a  solution  of  If  ozs.  of  blue 
vitriol  and  a  like  quantity  of  green  vitriol  in  1  quart  of  water, 
and  moistening,  when  dry,  with  a  solution  of  3J  ozs.  of  verdi- 
gris in  10J  ozs.  of  vinegar.     When  dry,  polish  the  object  with 
a  soft  waxed  brush  and  some  ferric  oxide.     The  coating  thus 
obtained  being  not  durable,  must  be  protected  by  a  coating 
of  lacquer. 

Durable  and  very  warm  sepia-brown  tone  upon  tin  and  its  al- 
loys.— Brush  the  object  over  with  a  solution  of  1  part  of  plat- 
inum chloride  in  10  of  water,  allow  the  coating  to  dry,  then 
rinse  in  water,  and,  after  again  drying,  brush  with  a  soft  brush 
until  the  desired  brown  luster  appears. 

A  dark  coloration  is  also  obtained  with  ferric  chloride  solu- 
tion. 

6.  Coloring  of  Silver. — See  "  Deposition  of  Silver.  " 
Electrochroma.     The  process  for  the  production  of  colors  on 

metals  by  electro-deposition,  known  under  this  term,  is  the 
invention  of  Mr.  F.  Arquimedas  Ktojaz.  By  this  method  either 
deposits  or  smuts  of  any  desired  color  or  texture  can  be  pro- 
duced upon  any  metal  used  as  a  cathode.  The  anodes  used 
are  of  pure  carbon,  no  metal  of  any  sort  being  put  into  the 
tank  containing  the  plating  solution  except  the  work  itself.  In 
starting  to  color  a  piece  of  metal,  be  it  brass,  copper,  tin,  lead 
or  iron,  etc.,  the  metal  is  first  dipped  into  a  cleaning  solution, 
then  into  a  hot  water  bath,  next  into  the  tank  containing  the 
solution  for  whatever  background  color  is  desired.  A  current 
of  8  to  12  volts  pressure  with  a  strength  of  1  ampere  per  square 
inch  of  surface  is  used.  After  an  immersion  in  the  tank  for 
from  two  to  three  minutes  the  work  is  dipped  into  hot  water, 
and  from  there  into  a  tub  containing  a  dip  solution.  Here  the 
finish  of  the  process  takes  place,  and  the  beautiful  shades  of 
color  are  produced.  A  piece  of  work,  such  as  a  lock  plate  for 
a  store,  may  be  given  a  green  verde  smut  in  the  plating  tank 
and  then  be  changed  to  a  light  blue  background  in  the  dip  tub- 
Gold  finishes,  rose  antique  and  green,  may  be  produced  at 


COLORING    OF    METALS.  537 

will  in  a  few  seconds  of  time,  without  any  gold  in  the  solu- 
tion. 

All  of  the  solutions  used  in  the  process  are  fully  protected 
by  patents  and  are  furnished  ready  for  use.  They  are  said  to 
be  made  up  of  more  than  half  a  dozen  elements,  the  propor- 
tions of  which  are  so  evenly  balanced  that  a  slight  variation 
in  the  amounts  used  of  each  ingredient  will  throw  the  entire 
solution  out  of  gear. 


CHAPTER  XV. 

LACQUERING. 

IN  the  electro-plating  industry  recourse  is  frequently  had  to 
lacquering  in  order  to  make  the  deposits  more  resistant  against 
atmospheric  influences,  or  to  protect  artificially  prepared  colors, 
patinas,  etc.  Thin,  colorless  shellac  solution,  which  does  not 
affect  the  color  of  the  deposit  or  of  the  patinizing,  is,  as  a  rule, 
employed,  while  in  some  cases  colored  lacquers  are  used  to 
heighten  the  tone  of  the  deposit,  as,  for  instance,  gold  lacquer 
for  brass. 

The  lacquer  is  applied  with  a  flat  fine  fitch  brush,  the  ob- 
ject having  previously  been  heated  hand-warm.  The  brush 
should  be  frequently  freed  from  an  excess  of  lacquer,  and  the 
lacquer  be  applied  as  uniformly  as  possible  without  undue 
pressure  of  the  brush.  An  excess  of  lacquer,  which  may  have 
been  applied,  is  removed  by  means  of  a  dry  brush. 

The  lacquer  for  immediate  use  is  kept  in  a  small  glass  or 
porcelain  pot,  across  the  top  of  which  a  string  may  be  stretched. 
This  string  is  intended  for  removing  by  wiping  the  excess  of 
lacquer  taken  up  by  the  brush.  Crusts  of  dried-in  lacquer 
should  be  carefully  removed,  and  the  contents  of  the  small  pot 
should  under  no  conditions  be  poured  back  into  the  can,  as 
otherwise  the  entire  supply  might  be  spoiled. 

After  lacquering,  the  object  is  dried  in  an  oven  at  a  temper- 
ature of  between  140°  and  158°  F.,  small  irregularities  being 
thereby  adjusted,  and  the  layer  of  lacquer  becoming  trans- 
parent, clear  and  lustrous. 

Electro-plated  articles  which  are  to  be  lacquered  must  be 
thoroughly  rinsed  and  dried  to  remove  adhering  plating  solu- 
tion from  the  pores,  otherwise  ugly  stains  will  form  under  the 

coat  of  lacquer. 

(538) 


LACQUERING.  539 

If  it  becomes  necessary  to  thin  a  spirit  lacquer,  only  absolute 
alcohol,  i.  e.t  alcohol  free  from  water,  should  be  used  for  the 
purpose,  since  alcohol  containing  water  renders  the  coat  of 
lacquer  muddy  and  dull. 

The  development  in  the  art  of  lacquer-making  has  advanced 
with  and  in  a  measure  kept  pace  with  that  made  in  the  electro- 
deposition  of  metals.  With  the  use  of  new  metals,  the  intro- 
duction of  new  and  altered  formulas  and  processes  for  finishing 
metals,  the  employment  of  new  and  different  chemicals,  in  fact 
with  every  change  or  alteration  in  the  methods  of  finishing 
and  using  metals,  changes  have  been  made  in  the  nature  of 
the  lacquers  employed  in  their  protection. 

Lacquers  to  be  acceptable  to  the  metal-worker  must  be  per- 
fectly adapted  to  each  special  use,  and  not  only  suit  the  varied 
metals,  finishes  and  conditions  of  the  work,  but  also  meet  and 
overcome  difficulties  arising  from,  for  instance,  the  influence  of 
climatic  changes  and  the  use  to  which  the  lacquered  metal  is 
subjected.  Many  cases  of  trouble  in  the  finishing  of  metal  may 
now  be  traced  to  the  use  of  an  improper  lacquer  for  the  par- 
ticular metal  or  finish.  Thus  ingredients  and  chemicals  which 
from  their  nature  are  antagonistic  to  a  bronze  metal  and  detri- 
mental to  it  should  not  be  included  in  a  lacquer  for  bronze, 
although  the  same  ingredients  may  be  beneficial  to  a  silver, 
gold  or  aluminium  surface. 

The  most  noted  improvements  have  been  effected  in  lacquers 
for  brass  bedsteads,  gas  arid  electric  fixtures,  black  lacquers, 
and  the  lacquers  made  with  the  special  object  of  saving  time 
in  their  application  and  money  in  their  use. 

A  review  of  all  the  lacquers  made  for  the  above-mentioned 
purposes  is  not  within  the  province  of  this  work,  and  w^  must 
therefore  confine  ourselves  to  the  enumeration  of  the  newest 
and  most  important  ones  for  general  use,  with  which  we  have 
become  familiar. 

Pyroxyline  lacquers. — These  lacquers,  known  under  various 
names,  such  as  Lastina,  Pyramide  and  Obelisk,  etc.,  were 
introduced  to  the  trade  in  America  as  early  as  1876,  and  were 


540  ELECTRO-DEPOSITION    OF    METALS. 

gradually  adopted  until  early  in  the  80's,  when  their  use  be- 
came general,  and  since  then  they  have  become  known 
throughout  all  parts  of  America  and  Europe.  Pyroxyline 
lacquer  represents  a  clear,  almost  colorless  fluid,  and  smells 
something  like  fruit-ether,  reminding  one  of  bananas.  It  is 
chiefly  used  as  a  dip  lacquer,  though  there  is  also  a  brush 
lacquer,  which  is  applied  with  a  brush,  like  spirit  lacquer. 

The  lacquer  possesses  the  following  good  properties :  The 
transparent,  colorless  coat  obtained  with  it  can  be  bent  with  the 
metallic  sheet  to  which  it  has  been  applied  without  cracking. 
It  is  so  hard  that  it  can  scarcely  be  scratched  with  the  finger- 
nail, shows  no  trace  of  stickiness,  and  it  is  perfectly  homogene- 
ous even  on  the  edges.  This  favorable  behavior  is  very  likely 
due  to  the  slow  evaporation  of  the  solvent,  and  the  fact  that  the 
lacquer  quickly  forms  a  thickish,  tenacious  layer,  which  though 
moved  with  difficulty  is  not  entirely  immobile.  Another  ad- 
vantage of  the  lacquer — especially  as  regards  the  metallic 
objects — is  that  the  coating  in  consequence  of  its  physical 
constitution  preserves  the  character  of  the  bases.  In  accord- 
ance with  the  nature  of  pyroxyline,  the  coating  is  not  sensibly 
affected  by  ordinary  differences  in  temperature,  and  does  not 
become  dull  and  non-transparent,  as  is  the  case  with  resins,  in 
consequence  of  the  loss  of  molecular  coherence.  It  can  be 
washed  with  water,  and  protects  metals  coated  with  it  from 
the  action  of  the  atmosphere.  It  may  also  be  colored,  but  of 
course  only  with  coloring  substances — mostly  aniline  colors — 
which  are  soluble  in  the  solvent  used. 

For  lacquering  articles  by  dipping,  they  should  be  as  clean 
as  for  plating,  and  so  arranged  that  the  lacquer  will  run  off 
propefly.  Allow  them  to  drip  over  the  drip  tank  until  the 
lacquer  stops  flowing.  Dry  in  a  temperature  of  100°  to  120° 
F.,  if  possible  using  a  thermometer.  Dip  lacquers  will  dry  in 
the  air,  but  baking  improves  the  finish. 

The  receptacle  for  holding  the  lacquer  and  thinner  for  dip- 
ping purposes,  should  be  either  of  glass,  stoneware,  chemically 
enameled  iron,  or  a  tin-lined  wooden  box — the  preference  be- 


LACQUERING.  541 

ing  in  the  order  named.  Lacquer  or  thinner  should  never  be 
placed  in  copper  or  galvanized  iron  tanks. 

For  thinning  the  lacquer  when  it  has  become  too  thick  by 
the  evaporation  of  the  solvent,  use  the  thinner  which  is  recom- 
mended for  each  particular  grade  of  lacquer. 

The  appearance  of  rainbow  colors  upon  objects  lacquered 
with  pyroxyline  lacquer  is  due  either  to  insufficient  cleanli- 
ness, especially  to  the  presence  of  grease  upon  the  objects,  or 
to  the  lacquer  having  been  too  much  diluted.  Objects  to  be 
lacquered  should  be  freed  from  grease  by  the  use  of  platers' 
compound,  rinsed  in  hot  water,  dried  in  thinner  and  then 
lacquered.  The  use  of  benzine,  aside  from  the  danger  it  en- 
tails, is  not  always  effective  in  removing  grease  from  the  pores 
of  the  metal.  After  cleaning,  the  polished  surface  of  the  work 
should  not  be  touched  with  the  hands.  If  the  rainbow  colors 
are  due  to  the  lacquer  having  been  too  much  thinned,  let  the 
vessel  containing  it  stand  uncovered  for  some  time  in  a  place 
free  from  dust,  so  that  it  becomes  somewhat  more  concentrated 
by  the  evaporation  of  the  solvent,  or  correct  the  tendency  to 
rainbow  colors  by  adding  more  undiluted  lacquer  to  the  mix- 
ture. In  adding  thinner  to  lacquer  it  is  always  advisable  to 
give  it  plenty  of  time  to  act  upon  the  pigment  in  the  lacquer. 
This  can  be  facilitated  by  stirring  with  a  wooden  paddle. 

Very  nice  shades  of  color  can  be  produced  by  coating  the 
objects,  previously  well  cleansed  from  grease,  with  lacquer  by 
dipping,  allowing  the  coat  to  become  dry,  then  suspending  the 
objects  for  a  few  seconds  in  golden-yellow,  red,  green,  etc., 
dyes,  known  as  dipping  colors,  next  washing  in  water  and 
finally  drying.  By  mixing  the  coloring  dyes  in  various  pro- 
portions nearly  every  desired  tone  of  color  can  be  obtained. 

Special  invisible  lacquer  for  ornamental  cast  and  chased  interior 
grille,  rail  and  enclosure  work.  This  lacquer  is  made  in  three 
grades  for  use,  1,  with  the  brush ;  2,  with  the  spraying 
machine  ;  and  3,  as  a  dip  lacquer.  Its  presence  cannot  be 
detected  on  any  of  these  sensitive  finishes,  and  the  fine  mat 
finishes  are  left  without  the  slightest  luster  after  it  has  been 


542  ELECTRO-DEPOSITION    OF    METALS. 

applied  thereto.  It  can  be  mixed  with  the  pigment  fillings 
so  much  used  in  cast  ornamental  mountings,  figured  mould- 
ing for  the  verds,  Florentine,  rose  and  antique  effects.  Sand- 
blasted and  brushed  plain  parts  will  not  take  on  a  sheen  from 
this  lacquer  and  will,  therefore,  not  make  a  contrast  in  the 
lights  of  the  filled  and  smooth  portions  of  the  work.  The 
fine  reliefs  in  these  finishes,  it  has  been  found,  will  not  be 
disturbed  because  of  the  lacquer  softening  the  pigments  when 
it  is  applied  by  spraying.  In  use  this  lacquer  can  be  thinned 
so  as  to  flow  away  from  the  various  parts  that  make  up  a 
grille  or  rail  without  leaving  any  lines  or  waves,  or  causing 
glossy  places  or  variations  of  lines.  This  lacquer  is  made  by 
The  Egyptian  Lacquer  Manufacturing  Co.,  of  New  York,  and 
with  it  the  rich  subdued  effects  of  dead,  mat,  sanded  and 
semi-dead  finishes  can  be  protected  without  in  the  least 
affecting  their  appearance. 

Satin  finish  lacquer  is  made  by  the  same  concern  just  men- 
tioned ;  it  comes  in  two  grades,  one  for  brush  and  the  other 
for  dip  work.  Its  purpose  is  to  maintain  the  light,  but  some- 
what solid,  effect  in  which  body  color  rather  than  tints  pre- 
dominate ;  its  deadness  gives  to  these  body  effects  a  plastic 
appearance.  It  can  be  used  to  protect  a  velvet-like  tint  re- 
sembling the  ground  gold,  frosting  or  satin  finish  seen  in 
ormolu  and  colonial  gold,  as  well  as  dead  and  dull  surfaces, 
or  unpolished,  lusterless  and  mat  gold  and  mat  silver.  It  can 
also  be  used  to  create  a  dead  luster,  or  a  deadened  lustrous 
surface,  for  example,  on  mat  designs  upon  a  lustrous  ground, 
where  the  lacquer  lights  up  the  satin  finish.  Jewelry,  silver 
and  novelty  manufacturers  can  use  it  for  general  finishing  of 
their  work,  as  it  will  not  alter  the  sensitive  metal  colorings, 
nor  will  it  fill  up  to  a  gloss  delicately  brushed,  satined,  or 
chased  surfaces  or  smut  tints. 

Dip  lacquer  for  pickled  castings  to  be  copper-plated  and  oxi- 
dized. Articles  made  from  iron  and  steel  castings  that  are 
pickled  or  water  rolled,  or  from  hot-rolled  steel,  where  the 
scale  is  pickled  off,  or  any  other  similar  work  which  is  pre- 


LACQUERING.  543 

pared  by  the  same  inexpensive  method,  when  copper-plated 
and  oxidized,  must  be  lacquered  with  a  lacquer  which  will 
give  life  to  the  naturally  dead  surface  of  the  metal  and  to  the 
smut  left  from  the  oxidation  when  not  scratch-brushed.  This 
is  a  very  rapid  and  inexpensive  process  since  it  does  away 
with  the  costly  operations  of  polishing,  scratch-brushing  and 
cleaning ;  the  finish  depends  entirely  upon  the  life  and  luster 
of  the  lacquer,  hence  it  is  best  to  use  one  of  the  lacquers  now 
designated. 

With  helios  dip  lacquer,  special,  which  is  made  by  The 
Egyptian  Lacquer  Manufacturing  Co.,  of  New  York,  a  fine 
luster  is  given  to  the  dead  backgrounds  and  a  bright  and 
lustrous  finish  to  the  smooth  parts  of  the  work  and  in  many 
respects  this  lacquer  renders  the  work  equal  to  that  which  has 
been  polished.  Many  other  lacquers  which  have  been  tried 
dry  down  to  the  natural  deadness  of  the  metal  finish  and 
consequently  the  effect  of  the  plating  and  oxidizing  is  lost,  or, 
if  not  entirely  lost,  is  not  brought  out  in  its  right  color. 

Old  brass  or  brush-brass  finishes.  From  90  to  95  per  cent  of 
all  brass  for  gas  and  electric  fixtures,  bedsteads  and  similar 
work  is  finished  in  brush-brass.  Lacquers  are  specially  made 
for  the  high  gloss  effects,  as  well  as  for  the  dull,  or  antique 
finish.  As  this  finish  is  more  susceptible  to  tarnish  and  stain 
than  any  other  known  finish,  it  is  important  that  precise 
particulars  be  given  as  to  the  handling  of  this  work  prelim- 
inary to  lacquering.  For  instance,  where  this  work  is  finished 
with  pumice,  sand,  flint,  etc.,  and  water,  as  most  of  it  is,  it 
should,  as  fast  as  completed  be  placed  in  a  tank  containing 
borax  solution  made  by  dissolving  1  Ib.  powdered  borax  in 
hot  water  and  adding  enough  water  to  make  5  gallons.  Use 
cold.  Let  the  work  accumulate  in  the  solution  until  ready 
to  lacquer.  Then  rinse  the  work  in  hot  water  and  dip  it  in 
thinner.  It  will  dry  without  stain  by  hanging  up  for  a 
moment  or  two,  when  it  should  be  immediately  lacquered. 

Where  "  old  brass  composition  "  or  emery  and  oil  is  used, 
the  work  should  be  cleaned  from  grease  in  "  plater's  com- 


544  ELECTRO-DEPOSITION    OF    METALS. 

pound  "  or  some  other  non-tarnishing  cleaner,  and  can  be 
placed  in  the  borax-solution  as  fast  as  finished  on  the  brush. 
It  is  then  rinsed  in  hot  (not  too  hot)  water,  dried  in  thinner, 
and  immediately  lacquered. 

Wiping  the  surface  with  a  soft  cloth  or  chamois  skin  does 
not  remove  the  moisture  from  the  metal.  This  is  particularly 
apparent  when  there  is  much  humidity  in  the  air,  and  ver- 
digris or  oxide  rapidly  forms  in  the  scratches  made  by  the 
abrasive  materials  and  causes  much  subsequent  trouble.  The 
heat  of  the  oven  converts  this  moisture,  combined  with  the 
oxide,  into  steam  which  penetrates  the  lacquer  and  causes 
staining  of  the  film.  Sawdust  should  never  be  used  for 
drying  metals  given  an  old-brass  finish. 

Brush  brass  finish  lacquers.  This  very  sensitive  and  easily 
discolored  finish  is  readily  marred  by  the  use  of  an  inefficient 
transparent  dip  lacquer.  No  existing  finish  requires  more 
exacting  and  careful  treatment  than  the  brush  brass  finish, 
the  finely  brushed  lines  attracting  and  retaining  substances 
which  tarnish  it  readily.  As  a  rule  these  substances  are  not 
visible,  and  cannot  be  easily  removed  by  ordinary  cleaning 
methods.  After  a  time  every  speck  of  dirt  shows  under  the 
lacquer  coating,  and  is  the  cause  of  the  various  discolorations 
often  seen  in  brush  brass  finish  ;  they  vary  from  the  tints 
shading  into  the  browns  to  tints  running  into  the  greens,  and 
are  in  almost  every  instance  caused  by  the  oxidizing  influ- 
ences of  contaminating  matters  left  upon  or  attracted  by  the 
metal  before  it  has  been  lacquered.  When  work  is  handled 
in  large  quantities  these  imperfections  are  especially  notice- 
able, for  such  work  cannot  always  be  inspected  one  piece  at  a 
time.  The  old  method  of  drying  the  buffed  and  smooth-sur- 
faced finishes  with  sawdust  and  then  rubbing  them  with  a  soft 
muslin  material  is  inadequate  as  well  as  uncertain  for  the 
brush  brass ;  in  fact  this  process  primarily  causes  the  imper- 
fections which  it  is  intended  to  prevent.  At  any  rate,  the 
result  is  necessarily  doubtful  when  brush  brass  is  dried  in  this 
way  and  allowed  to  stand  for  even  a  very  short  time  before  it 
is  protected  with  lacquer. 


LACQUERING.  545 

Egyptian  brush  brass  dip  lacquer  and  brush  brass  thinner, 
made  by  the  Egyptian  Lacquer  Manufacturing  Co.,  of  New 
York,  meets  the  necessary  and  varied  conditions  called  for  by 
this  finish.  After  the  brush  brass  has  been  washed  in  plater's 
compound  and  well  rinsed  in  cold  and  hot  waters,  the  work 
is  first  dipped  into  the  brush  brass  thinner,  which  absorbs  all 
moisture  left  on  the  metal  and  removes  whatever  impurities 
may  have  been  attracted  to  it,  and  prepares  the  work  for  its 
dip  into  the  brush  brass  dip  lacquer.  By  the  dip  into  the 
thinner  a  chemically  pure  metal  surface  is  provided  for  the 
reception  of  the  lacquer  coating,  and  this  guarantees  the  brush 
brass  finish  itself  against  discoloration,  since  the  lacquer  has 
been  applied  to  a  practically  chemically  clean  and  pure 
surface. 

Brush  brass  work  which  cannot  be  conveniently  dip- 
lacquered  should  be  spray-lacquered  in  preference  to  lacquer- 
ing with  a  brush,  because  the  fine  irregularities  of  the  brushed 
surface  of  the  metal  retard  the  free  flow  of  a  brush  lacquer. 
In  other  words,  a  brush  lacquer  cannot  be  applied  quite  as 
effectively  as  on  a  smooth  finish,  for,  owing  to  the  irregu- 
larities of  the  metal  surface  spoken  of,  an  obstruction  is  placed 
in  the  way  of  the  flowing  of  the  lacquer  when  it  is  applied 
with  a  brush,  because  with  the  use  of  the  latter  the  separa- 
tions in  the  lacquer,  due  to  the  uneven  distribution  of  it  from 
the  bristles  of  the  brush,  sometimes  leave  minute  parts  of  the 
surface  unlacquered  and  the  irregularities  of  the  brushed 
metal  surface  prevent  the  lacquer  from  spreading  over  these 
minutely  exposed  lines.  Thus  when  applying  the  lacquer 
with  a  brush  it  happens  now  and  then  that  the  exposed  and 
unlacquered  portions  tarnish  and  destroy  the  appearance  of 
the  entire  work.  On  large  articles  the  lacquer  should  be 
sprayed,  and  the  article  itself  turned  by  mechanical  means 
during  the  application  of  the  lacquer,  so  as  to  give  momentum 
to  its  flow,  thereby  insuring  its  even  distribution. 

Brass  bedstead   lacquering.     Complaints  of  the  same  kind, 
namely,  streaks  in  lacquered  work,  have  been  the  cause  for 
35 


546  ELECTRO-DEPOSITION    OF    METALS. 

replacing  brush  lacquering  of  brass  bedsteads  by  the  spray. 
Since  the  vogue  for  satin  and  drawn  emery  finishes  have  taken 
the  place  of  the  old  English  gilt  bedstead  finish  the  spraying 
process  has  become  even  more  necessary.  The  unusual  depth 
of  the  cut  in  the  metal  surface  made  by  these  finishes  has  cre- 
ated a  new  problem  for  lacquer  makers.  The  lacquer  used  on 
this  work  should  be  unusually  heavy,  in  fact  heavy  enough 
and  dense  enough  to  fill  these  abnormally  penetrated  surfaces, 
for  the  lacquer  film  must  in  all  instances  be  built  up  so  as  to 
protect  the  highest  exposed  points  of  this  finish.  The  lacquer 
for  this  finish  must  be  applied  with  a  spray  since  it  is  neces- 
sary that  a  thick  and  plastic  coating  should  be  applied,  one 
indeed  which  when  dry  shall  be  hard  and  tough  enough  to 
resist  marring  from  the  usual  rough  and  severe  treatment  to 
which  a  bedstead  is  subjected. 

Dead  black  lacquers  produce  imitation  dead  and  mat  finishes. 
These  are  variously  known  as  imitation  Bower  Barff,  wrought 
iron,  ebony  or  rubber  finishes.  If  the  same  preliminary  steps 
are  taken  in  preparing  metal  goods  for  the  black  lacquers  as 
for  japan  and  enamel,  just  as  durable  and  lasting  results  will 
be  obtained  in  a  small  fraction  of  the  time  and  at  a  minimum 
cost  in  labor.  The  best  class  of  japanning  on  iron  castings, 
hot  or  cold  rolled  steel  requires  two  coats  of  either  thin  japan 
or  some  other  similar  preparation,  each  coat  requiring  several 
hours'  baking,  and  usually  a  delay  of  several  days  before  the 
surface  of  the  last  coat  is  in  condition  to  be  rubbed  down. 

To  get  the  same  results  with  the  black  lacquers  on  sand 
pitted  cast  iron,  two  coats  of  metallic  filler,  applied  with  a  brush, 
baked  a  short  time  at  about  180°  F.  to  harden,  and  then 
rubbed  down  with  fine  emery  cloth  or  No.  2  garnet  paper,  fol- 
lowed by  one  or  two  air-drying  coats  of  lacquer  will  be  suffi- 
cient. On  smooth-surfaced  metals  one  or  two  thin  coats  of 
lacquer  can  be  applied  in  place  of  the  metallic  filler  as  a  base 
for  the  final  coat.  In  many  cases  one  coat  of  the  lacquer  will 
be  found  sufficient  to  give  the  desired  finish,  and  the  entire 
process  may  be  completed  in  a  few  hours,  where  it  will  re- 


LACQUERING.  547 

quire  from  one  to  five  days  to  secure  the  same  finish  with 
japan,  and  besides  all  the  equipment  necessary  for  the  latter 
will  be  entirely  eliminated. 

If  desired,  the  metal  can  be  given  a  light  copper  plate  and 
then  be  oxidized  as  a  base  for  the  finishing  coat  of  black 
lacquer. 

For  high  luster  finishes  such  as  are  obtained  with  enamels, 
glossy,  black  lacquers  are  used,  and  to  increase  the  brilliancy 
and  high  luster  the  same  as  with  enameled  goods  which  are 
given  a  finishing  coat  of  baking  varnish,  a  high  grade  of 
transparent  lacquer  is  used  over  the  glossy  black  lacquer  the 
same  as  the  varnish  on  the  enamel. 

On  goods  made  from  non-ferrous  metals  such  as  high-grade 
optical  goods,  opera  and  field  glasses,  and  all  classes  of  instru- 
ment work,  where  sliding  tubes  and  other  parts  are  to  be 
finished  with  a  glossy  or  dead  black  lacquer,  where  both 
beauty  and  great  durability  are  the  chief  essentials,  the  surface 
of  the  brass  should  be  first  prepared  by  chemically  blacking 
the  metal  with  copper-ammonia  or  any  other  good  black  dip. 
Then  a  filling  coat  of  any  black  lacquer,  preferably  a  dead 
black,  should  be  used.  The  surface  is  then  in  perfect  condition 
for  the  finishing  coat  of  black  lacquer.  A  black  background 
and  very  adhesive  surface  are  obtained  by  this  method,  and  the 
finish  will  withstand  the  hard  usage  these  goods  are  made  for. 

Dead  black  lacquer  as  a  substitute  for  Bower-Barff.  The 
genuine  Bower-Barff  is  a  matted  black  finish  for  iron  and 
steel.  It  is  produced  by  heat  and  steam  liberating  the  oxygen 
from  the  iron  and  forming  magnetic  oxide. 

The  oven  and  other  equipment  required  for  this  finish  is 
not  practicable  in  the  average  factory,  as  the  demand  for 
goods  in  this  finish,  outside  builders'  hardware,  is  not  com- 
mensurate with  the  cost  of  providing  and  maintaining  a  plant 
for  this  purpose. 

A  number  of  imitation  finishes  are  made,  by  using  solutions 
of  sulphur  and  linseed  oil,  sulphur,  graphite  and  turpentine, 
and  other  similar  solutions.  A  coating  of  these  mixtures  is 


548  ELECTRO-DEPOSITION    OF    METALS. 

applied  and  the  metal  heated  to  a  red  heat  to  burn  it  in  or 
else  the  goods  are  baked  in  a  muffle.  But  they  are  all  slow 
and  uncertain  processes,  and  some  kind  of  special  equipment 
must  be  provided  to  do  this  work. 

The  method  for  obtaining  this  finish  most  in  use,  and  for 
which  any  plating-room  is  equipped,  is  by  using  an  antique 
black  or  Bower-Barff  lacquer.  Such  lacquer  has  a  number  of 
advantages  over  the  above-described  processes,  which  can 
only  be  used  on  iron  or  steel ;  the  lacquer  will  give  the  finish 
on  any  metal. 

To  get  the  Bower-Barff  on  iron  or  steel  the  metal  should 
first  be  lightly  copper-plated  and  oxidized  ;  and  if  brass  or 
bronze  is  used  it  is  only  necessary  to  oxidize  the  metal  with 
any  black  dip,  or  electro-oxidize.  Then  the  antique  black 
lacquer  is  applied  for  the  finish.  The  lacquer  can  also  be 
lightly  sand-blasted  if  an  increased  mat  is  desired. 

In  the  above-described  processes  good  results  are  obtained 
by  the  use  of  the  following  lacquers,  made  by  the  Egyptian 
Lacquer  Manufacturing  Co.  of  New  York  :  Dead  Blacks,  Egyp- 
tian Antique  Blacks,  Ebony,  and  Rubber  Finish  Lacquers. 

Spraying  of  lacquers. — The  application  of  lacquers  by  the 
pneumatic  air  spray  having  for  the  last  few  years  been  gradu- 
ally adopted,  has  proved  advantageous  in  finishing  various 
goods,  the  success  in  application  depending  upon  many  minor 
details  of  manipulation  ;  these  come  readily  to  the  lacquerer 
while  using  the  spray. 

The  spraying  machine  consists  of  a  pump,  called  a  com- 
pressor, generating  the  air,  transferring  the  air  to  a  storage 
tank.  If  this  pump  is  automatic,  copper  flexible  tubing  is 
used,  if  stationary,  a  gas  pipe.  The  storage  tank  which  holds 
the  air,  has  a  gauge  indicating  the  number  of  pounds  carried. 
A  safety  valve  is  also  on  the  tank  to  control  the  air.  These 
tanks  vary  a  great  deal ;  it  depends  entirely  upon  the  number 
of  cups  drawing  off  the  air  and  the  air  must  be  regulated  ac- 
cordingly. It  will  run  from  18  Ibs.,  and  in  some  cases  as 
high  as  60.  There  is  a  rubber  hose  of  flexible  copper  tube 


LACQUERING.  549 

connected  to  the  storage  tank  long  enough  to  cover  the  entire 
work -bench  to  which  the  cups  are  fastened.  The  cup  or  con- 
tainer is  an  atomizer  throwing  a  spray  very  much  the  same  as 
a  perfume  atomizer,  although  it  is  made  in  sizes  from  half  a 
pint  to  a  quart.  Cups  or  containers  are  made  both  of  glass 
and  metal.  Some  prefer  the  glass  for  the  reason  that  it  is 
possible  to  see  the  lacquer  in  the  container  at  any  time.  Glass 
cups  have,  however,  the  drawback  of  liability  of  breakage 
which  may  result  from  careless  or  rough  usage  about  the  shop, 
and  besides  some  sprays  are  so  constructed  that  under  certain 
conditions  it  is  an  easy  matter  for  the  air  pressure  to  be  acci- 
dentally switched  directly  into  the  container,  and  with  a  pres- 
sure of  40  Ibs.  both  container  and  lacquer  are  destroyed.  For 
these  reasons  it  would  seem  that  metal  containers  are  to  be 
preferred.  The  spray  may  be  gauged  by  a  small  catch  on  the 
side  of  the  nozzle.  This  style  of  sprayer  is  considered  very 
practical,  although  there  are  many  more  complicated  ones  in 
the  market. 

The  equipment  to  be  used  in  producing  the  air,  storing  it 
and  in  forcing  it  to  the  spray  in  a  pure  condition  should  be 
of  sufficient  capacity  and  be  provided  with  the  proper  appli- 
ances to  guard  against  fluctuations  which  in  the  flow  of  the 
lacquer  stream  itself  interferes  with  the  continuous  flow  of  the 
lacquer.  This  flow  of  necessity  must  be  uniform  in  strength 
and  outflow,  else  the  results  cannot  fail  to  be  irregular.  It 
naturally  follows  that  the  compressor  which  regulates  this 
must  be  such  as  to  be  capable  of  sustaining  this  pressure 
uninterruptedly.  The  quality  of  the  lacquering  changes  with 
the  irregularity  of  the  pressure.  The  air  should  be  taken 
from  a  part  of  the  building  which  is  far  removed  from  the 
steam  exhausts  or  other  localities  where  the  air  or  atmosphere 
is  impure  or  moist ;  the  drier  the  air,  the  less  condensed  water 
will  enter  into  the  pipe  line.  The  air  should  be  stored  in  a 
tank  close  to  where  the  spray  is  in  use,  for  this  helps  in  the 
precipitating  of  impurities  just  before  it  goes  into  the  lacquer, 
and  the  extra  volume  close  at  hand  steadies  the  pressure.  A 


550  ELECTRO-DEPOSITION    OF    METALS. 

reducing  valve  in  the  line  between  the  tank  and  spray,  which 
can  be  drained  occasionally,  is  another  precaution  which  may 
be  provided  against  the  admission  of  water.  The  addition  of 
a  filter  will  be  found  to  be  of  great  advantage,  as  it  will  catch 
the  most  minute  particles  of  oil,  moisture  and  dirt  just  before 
the  air  reaches  the  flexible  hose  to  which  the  spray  is  attached. 

Assuming  that  both  the  pressure  and  clean  air  referred  to 
can  be  relied  upon,  then  the  next  thing  necessary  is  to  use 
the  lacquer  in  as  heavy  a  condition  as  possible.  By  this  is 
meant  that  it  should  be  neither  too  heavy  nor  too  light  for 
the  air  to  raise  it  to  the  nozzle,  atomize  it  and  apply  it  by 
flowing  it  out  from  the  spray  upon  the  work  in  an  even  and 
heavy  film. 

The  lacquer  should  never  be  thinned  so  as  to  make  it  easier 
in  the  spray,  for  in  that  case  the  lacquer  will  create  runs  upon 
the  surface  of  the  work;  if  unusual  thinning  is  necessary  to 
get  an  even  flow  from  the  spray  then  either  the  pressure  or 
the  adjustment  of  the  spray,  or  the  spray  itselt,  is  at  fault. 
While  the  lacquer  is  being  applied  from  the  spray  the  work 
which  is  being  lacquered  should  be  kept  moving  in  a  revolv- 
ing motion  in  order  to  insure  an  even  distribution  of  the  lac- 
quer, and  avoid  an  uneven  distribution  of  it ;  in  other  words, 
to  prevent  matting. 

The  high  pressure  used  drives  the  lacquer  onto  the  object, 
after  which,  however,  the  liquid  must  take  care  of  itself,  and 
it  must  then  flow  together  into  a  smooth  surface,  or  else  the 
whole  process  is  worthless. 

The  spraying-on  of  lacquers  to  be  successfully  used  depends 
not  only 'upon  the  nature  of  the  articles  sprayed,  but  upon  the 
lacquer  itself.  Special  lacquers  have  been  made  for  these  pur- 
poses, and  with  them  success  may  readily  be  obtained.  A 
special  lacquer  has  been  made  for  lamps,  chandeliers  and  gas 
fixtures  ;  another  for  silver  and  white  metals ;  another  'for 
builders'  hardware.  With  these  when  applied  uniformly,  the 
lacquer  spreads  evenly  and  covers  the  surface  entirely  with- 
out break,  and  presents  an  unusually  uniform  appearance  with- 


LACQUERING.  551 

out  disfiguring  blotches  or  patches,  indicating  an  unequal  thick- 
ness of  lacquer. 

Most  of  the  lacquers  which  we  have  seen  tested  were  made  by 
The  Egyptian  Lacquer  Manufacturing  Company  of  New  York. 
In  many  instances  it  will  be  found  that  ordinary  operators 
with  less  skill  than  the  trained  lacquerer  can  do  very  satisfac- 
tory work  with  these  machines. 

Spraying  black  lacquers.  By  applying  the  black  lacquers 
with  a  spray  various  finishes  heretofore  made  with  either 
baking  enamels  or  japans  can  now  be  finished  with  black 
lacquer.  Whenever  great  durability  and  toughness  are  essen- 
tial and  where  the  fine  finish  made  with  the  black  lacquer  is 
but  a  secondary  consideration,  a  priming  lacquer  should  be 
first  applied  to  the  work  ;  after  this  the  black  lacquer  should 
be  sprayed  over  it.  Such  a  finish  makes  up  in  toughness  and 
tenacity  the  slight  runs  in  its  appearance.  A  second  coating 
of  black  lacquer  without  this  priming  coat  will  not  be  proof 
against  the  hard  usage  to  which  some  of  these  finishes  are 
frequently  exposed. 

A  coat  of  priming  lacquer  is  of  great  advantage  in  many 
instances  where  the  metal  surface  is  not  of  an  adhesively 
magnetic  nature,  or  on  a  metal  that  cannot  be  entirely  pre- 
vented from  taking  an  oxide  if  exposed  to  the  air  even  only 
during  the  short  time  of  lacquering.  The  coat  of  priming 
lacquer  is  also  a  desirable  preventative  where  large  quan- 
tities of  work  are  being  lacquered  and  where  cleanliness  of 
the  work  cannot  always  be  absolutely  relied  upon.  Peeling 
and  chipping,  either  or  both,  are  often  caused  by  the  inex- 
perience of  the  lacquerer  in  mixing  the  lacquer ;  if  the  body 
is  thinned  to  the  extent  that  it  weakens  the  binding  qualities 
of  the  material  something  of  the  kind  is  bound  to  happen. 

Since  the  advent  of  antique  effects,  such  as  mission  and 
Flemish,  and  other  dark  and  subdued  finishes  on  furniture, 
etc.,  the  manufacturers  of  art  metal  goods  have  given  close 
attention  to  having  their  goods  in  conformity  with  the  furni- 
ture and  trimmings  in  buildings. 


552  ELECTRO-DEPOSITION    OF    METALS. 

I 

They  have  found  the  dead  black  lacquers  the  best  for  this  * 
purpose,  and  the  question  of  application  has  been  solved  by 
the  spray,  as  it  was  impossible  to  get  the  fine  results  they  re- 
quire by  either  brushing  or  dipping  the  black  lacquers,  for 
unless  the  operator  was  skilled  in  the  application  of  lacquers 
by  these  methods  there  would  be  such  imperfections  as  streaks, 
laps,  runs  or  drip.  With  the  spray  all  these  difficulties  are 
obviated  and  the  finish  cannot  be  otherwise  than  perfect,  and 
the  lacquer  thereby  used  to  the  best  advantage,  with  the  fine 
result  intended  for  it  by  the  makers. 

To  use  the  spray  successfully  for  this  purpose,  the  base  used 
in  the  lacquer  must  be  adapted  to  go  through  the  spray 
nozzle  without  clogging  and  going  onto  a  surface  lumpy. 
With  the  spray  any  of  the  blacks  proposed  by  The  Egyptian 
Lacquer  Manufacturing  Co.  can  be  applied  on  all  classes  of 
metals,  whether  of  a  design  with  deep  indentations  or  inter- 
stices or  on  the  flattest  surface,  with  artistic  perfection. 

The  same  can  be  said  about  the  finishing  of  other  goods, 
such  as  slate  electric  switchboards,  gas  stoves,  heaters,  steel  or 
other  box  enclosures,  cast  parts,  steel  or  brass  stampings,  or,  in 
fact,  all  other  articles  made  from  any  of  the  metals  or  any  of 
the  alloys. 

The  black  lacquers  will  retain  their  original  finish  and  re- 
main black  under  heat.  And  there  is  no  other  black  made 
that  will  adorn  this  class  of  goods  the  same  from  the  points  of 
beauty,  durability  and  salableness.  Stoves  and  heaters  have 
large  and  porous  surfaces  as  the  sheet  metal  is  left  in  its 
natural  condition  just  as  it  comes  from  the  rolling  mill,  and 
for  this  reason  it  has  been  found  difficult  to  apply  the  black 
lacquer  with  a  brush,  but  the  spray  puts  it  on  perfectly,  and 
transforms  it  from  an  object  of  roughness  to  one  of  uni- 
formity. To  avoid  marring  the  nickel  trimmings  during  the 
operation  of  spraying,  a  mask  or  other  covering  is  used  to 
protect  those  parts,  and  it  is  then  a  very  rapid  process. 

This  also  applies  to  all  other  articles  constructed  from  the 
same  material  and  on  the  same  order  of  the  stoves  and  heaters. 


LACQUERING.  553 

On  other  metal  goods,  where  designs  or  ornaments  are  to  be 
put  on,  with  black  or  other  colored  lacquers,  stencils  are  used, 
and  the  lacquers  sprayed  onto  it.  With  the  spray  application 
there  will  be  no  runs  or  other  disfigurement  of  the  design. 

The  spray,  with  the  blacks  or  other  colored  lacquers,  can 
be  used. 

Water-dip  lacquers  and  their  use. — These  lacquers  are  not,  as 
often  believed,  lacquers  in  which  water  is  used.  Their  name 
is  derived  from  the  fact  that  after  the  metal  has  been  dipped 
or  plated,  it  may,  while  wet  and  without  drying  it,  be  dipped 
into  the  lacquer  without  in  any  way  affecting  the  metal  finish. 

The  advantage  of  water-dip  lacquers  is  readily  appreciated 
by  the  manufacturers  who  are  rapidly  adopting  them  for  many 
€lasses  of  small  work.  They  are  especially  well  adapted  for 
bright-dipped  finishes,  such  as  are  usually  finished  in  bulk  by 
basket  dipping.  Tarnish  affects  this  finish  almost  instantly 
if  it  is  allowed  to  dry  and  then  lacquered  in  the  usual  way  ; 
therefore  the  lacquering  must  be  carried  out  as  soon  as  the 
dipping  process  has  been  finished. 

The  most  flagrant  example  of  tarnishing  is  in  the  case  of 
plated  work,  particularly  goods  copper-plated,  and  to  prevent 
tarnishing,  such  goods  must  be  lacquered  at  once.  Even  the 
customary  drying-out  will  usually  not  suffice  to  prevent  the 
tarnishing,  and  the  result  is  either  the  increase  in  labor  in 
handling  the  goods,  or  the  production  of  a  large  amount  of 
imperfect  goods. 

The  method  of  drying  work  in  sawdust  before  lacquering, 
with  the  consequent  carrying  of  sawdust  into  the  lacquer,  and 
the  frequent  discoloration  of  the  finish  by  wet  sawdust,  can  be 
entirely  eliminated,  and  this  one  important  improvement 
alone  in  handling  such  work  has  brought  about  an  extensive 
use  for  the  water-dip  lacquers. 

Since  the  advent  of  mechanical  platers  water-dip  lacquers 
have  another  and  new  field,  as  the  goods  plated  in  this  way 
can  be  put  into  a  mesh  basket  as  soon  as  taken  from  the  plater 
and  lacquered,  which  not  only  gives  the  finish  immediate  pro- 


554  ELECTRO-DEPOSITION    OF    METALS. 

tection  but  is  in  keeping  with  the  quickness  and  low  cost  of 
this  method. 

Points  to  follow  when  using  water-dip  lacquers  for  small  work, 
such  as  cupboard  catches,  window  fasteners,  cheap  building 
and  trunk  hardware,  coat  hooks,  tacks,  furniture  nails,  and 
other  small  specialties  and  novelties.  The  work  may  be  placed 
in  a  wire  mesh  basket,  rinsed  in  cold  and  hot  water,  dipped 
into  the  lacquer,  which  can  be  used  so  thin  that  there  will  be 
no  accumulation  or  drip  left,  and  the  work  can  be  dried  in 
bulk  without  the  pieces  sticking  together.  The  goods  thus 
lacquered  can  be  put  right  into  a  box  and  sent  to  the  shipping 
room  where  they  will  dry  out  hard  and  with  a  high  luster. 

The  water-dip  lacquers,  made  by  The  Egyptian  Lacquer 
Manufacturing  Company  of  New  York,  contain  ingredients 
which  permit  lacquering  in  bulk  of  small  brass-plated  work? 
copper  acid-dipped  or  oxidized  finishes  being  rinsed  in  either 
hot  or  cold  water,  and  without  drying  dipped  directly  into  the 
lacquer.  Electro-deposited  copper  oxidizes  rapidly,  and  espe- 
cially so  in  a  humid  atmosphere.  An  instant  application  of 
these  lacquers,  while  the  work  still  retains  its  luster  is  recom- 
mended. It  is  very  desirable  for  bulk,  basket  or  en-masse 
lacquering. 

A  large  collection  of  small  articles  can  be  perfectly  lacquered 
by  simple  immersion. 

Syphon  out  the  water  every  morning  from  the  lacquering 
tank,  either  with  a  rubber  hose  or  by  means  of  a  faucet  at  the 
bottom  of  the  tank. 

A  wire  screen,  nickel-plated  and  with  a  coarse  mesh,  should 
be  placed  in  the  lacquer  jar  or  tank,  three  or  four  inches  from 
the  bottom.  This  will  prevent  the  work  from  being  dipped 
through  the  lacquer  into  the  precipitated  water,  which  lies  at 
the  bottom  of  the  jar.  All  dirt  and  foreign  matter  carried  into 
the  lacquer  with  the  work  will  sift  through  the  screen  and  can 
be  drawn  off  with  the  water. 


CHAPTER  XVI. 

i 

HYGIENIC    RULES    FOR    THE    WORKSHOP. 

IN  but  few  other  branches  of  industry  has  the  workman  so 
constantly  to  deal  with  powerful  poisons  as  well  as  other  sub- 
stances and  vapors,  which  are  exceedingly  corrosive  in  their 
action  upon  the  skin  and  the  mucous  membranes,  as  in  electro- 
plating. However,  with  ordinary  care  and  sobriety,  all  influ- 
ences injurious  to  health  may  be  readily  overcome. 

The  necessity  of  frequently  renewing  the  air  in  the  workshop 
by  thorough  ventilation  has  already  been  referred  to  in  chapter 
IV,  "  Electro-plating  Establishments  in  General."  Workmen 
exclusively  engaged  in  pickling  objects  are  advised  to  neutral- 
ize the  action  of  the  acid  upon  the  enamel  of  the  teeth  and  the 
mucous  membrane  of  the  mouth  and  throat  by  frequently 
rinsing  the  mouth  with  dilute  solution  of  bicarbonate  of  soda. 
Those  engaged  in  freeing  the  objects  from  grease  lose,  for  want 
of  cleanliness,  the  skin  on  the  portions  of  the  fingers  which 
come  constantly  in  contact  with  the  lime  and  caustic  lyes. 
This  may  be  overcome  by  frequently  washing  the  hands  in 
clean  water;  and  previous  to  each  intermission  in  the  work  the 
workman  should,  after  washing  the  hands,  dip  them  in  dilute 
sulphuric  acid,  dry  them,  and  thoroughly  rub  them  with  cos- 
moline,  or  a  mixture  of  equal  parts  of  glycerine  and  water. 
The  use  of  rubber  gloves  by  workmen  engaged  in  freeing  the 
objects  from  grease  cannot  be  recommended,  they  being  ex- 
pensive and  subject  to  rapid  destruction.  It  is  better  to  wrap 
a  linen  rag  seven  or  eight  times  around  a  sore  finger,  many 
workmen  using  this  precaution  to  protect  the  skin  from  the 
corrosive  action  of  the  lye. 

It  should  be  a  rule  for  every  employee  in  the  establishment 
not  to  drink  from  vessels  used  in  electro-plating  manipula- 

(555) 


556  ELECTRO-DEPOSITION    OF    METALS. 

tions  ;  for  instance,  porcelain  dishes,  beer  glasses,  etc.  One 
workman  may  this  moment  use  such  a  vessel  to  drink  from, 
and  without  his  knowledge  another  may  employ  it  the  next 
morning  for  dipping  out  potassium  cyanide  solution,  and  the 
first  using  it  again  as  a  drinking  vessel  may  incur  sickness,  or 
even  fatal  poisoning. 

The  handling  of  potassium  cyanide  and  its  solutions  re- 
quires constant  care  and  judgment.  \Working  with  sore  hands 
in  such  solutions  should  be  avoided  as  much  as  possible ;  but 
if  it  has  to  be  done,  and  the  workman  feels  a  sharp  pain  in 
the  sore,  wash  the  latter  quickly  with  clean  water,  and  apply 
a  few  drops  of  blue  vitriol  solution. 

Many  individuals  are  very  sensitive  to  nickel  solutions, 
eruptions  which  are  painful  and  heal  slowly  breaking  out 
upon  the  arms  and  hands,  while  others  may  for  years  come  in 
contact  with  nickel  baths  without  being  subject  to  such  erup- 
tions. In  such  cases  prophylaxis  is  also  the  safeguard,  i.  e., 
to  prevent  by  immediate  thorough  washing  the  formation  of 
the  eruption  if  the  skin  has  been  brought  in  contact  with  the 
nickel  solution,  as,  for  instance,  in  taking  out  with  the  hand 
an  object  which  has  dropped  into  a  nickel  bath. 

Poisoning  by  prussic  acid,  potassium  cyanide  and  cyanide  com- 
binations.— In  cases  of  internal  poisoning^  first  aid  must  be 
quickly  rendered  and  a  physician  immediately  called.  There 
is  but  little  hope  of  saving  the  life  of  a  person  poisoned  b}7 
prussic  acid,  as  well  as  when  potassium  cyanide  or  soluble 
cyanide  combinations  in  large  quantities  have  been  taken  into 
the  stomach.  In  such  cases  solution  of  acetate  of  iron  should 
be  quickly  administered  and  the  patient  made  to  inhale  some 
chlorine  prepared  by  putting  a  teaspoonful  of  chloride  of  lime 
in  water  acidulated  with  a  small  quantity  of  sulphuric  acid. 
Water  as  cold  as  possible  should  at  intervals  be  also  poured 
over  the  head  of  the  patient. 

Poisoning  by  copper  salts. — The  stomach  should  be  quickly 
emptied  by  means  of  an  emetic  or,  in  want  of  this,  the  patient 
should  thrust  his  finger  to  the  back  of  his  throat  and  induce 


HYGIENIC    RULES    FOR    THE    WORKSHOP.  557 

vomiting  by  tickling  the  uvula.  After  vomiting,  drink  milkr 
white  of  egg,  gum-water,  or  some  mucilaginous  decoction. 

Poisoning  by  lead  salts  requires  the  same  treatment  as  poison- 
ing by  copper-salts.  A  lemonade  of  sulphuric  acid,  or  an  alka- 
line solution  containing  carbonic  acid,  such  as  Vichy  water  or 
bicarbonate  of  soda,  is  also  very  serviceable. 

Poisoning  by  arsenic. — The  stomach  must  be  quickly  emptied 
by  an  energetic  emetic,  when  freshly  precipitated  ferric  hydrate 
and  calcined  magnesia  may  be  given  as  an  antidote.  Calcined 
magnesia  being  generally  on  hand,  mix  it  with  15  or  20 
times  the  quantity  of  water,  and  give  of  this  mixture  5  or  6 
tablespoonfuls,  every  10  to  15  minutes. 

Poisoning  by  alkalies. — Use  weak  acids,  such  as  vinegar, 
lemon  juice,  etc.,  and  in  their  absence  sulphuric,  hydrochloric 
or  nitric  acid  diluted  to  the  strength  of  lemonade.  After  the 
pain  in  the  stomach  has  diminished,  it  will  be  well  to  adminis- 
ter a  few  spoonfuls  of  olive  oil. 

Poisoning  by  mercury  salts. — Mercury  salts,  and  particularly 
the  chloride  (corrosive  sublimate),  form  with  the  white  of  egg 
(albumen)  a  compound  very  insoluble  and  inert.  The  remedy, 
albumen,  is  therefore  indicated.  Sulphur  and  sulphuretted 
water  are  also  serviceable  for  the  purpose. 

Poisoning  by  sulphuretted  hydrogen. — The  patient  should  be 
made  to  inhale  the  vapor  of  chlorine  from  chlorine  water, 
Javelle  water,  or  bleaching-powder.  Energetic  friction,  espe- 
cially at  the  extremities  of  the  limbs,  should  be  employed. 
Large  quantities  of  warm  and  emollient  drinks  should  be  given, 
and  abundance  of  fresh  air. 

Poisoning  by  chlorine,  sulphurous  acid,  nitrous  and  hyponitric 
gases. — Admit  immediately  an  abundance  of  fresh  air,  and  ad- 
minister light  inspirations  of  ammonia.  Give  plenty  of  hot 
drinks  and  excite  friction  in  order  to  conserve  the  warmth  and 
transpiration  of  the  skin.  Employ  hot  foot-baths  to  remove 
the  blood  from  the  lungs.  Afterwards  maintain  in  the  mouth 
of  the  patient  some  substance  which,  melting  slowly,  will  keep 
the  throat  moist,  such  as  jujube  and  marshmallow  paste,  mo- 
lasses candy,  and  licorice  paste.  Milk  is  excellent. 


CHAPTER  XVII. 

GALVANOPLASTY    (REPRODUCTION). 

BY  galvanoplasty  proper  is  understood  the  production,  with 
the  assistance  of  the  electric  current,  of  copies  of  articles  of 
various  kinds,  true  to  nature,  and  of  sufficient  thickness  to 
form  a  resisting  body,  which  may  be  detached  from  the  object 
serving  as  a  mould. 

By  means  of  galvanoplasty  we  are  enabled  to  produce  a 
simple,  smooth  plate  of  copper  of  such  homogeneity  as  never 
shown  by  rolled  copper,  and  such  copper  plates  are  used  for 
engraving.  From  a  medal,  copper-engraving,  type  or  other 
metallic  object,  a  galvanoplastic  copy  may  be  made,  which  is 
to  be  considered  as  the  negative  of  the  original,  in  so  far  as  it 
shows  the  raised  portions  of  the  original  depressed,  and  the 
depressed  portions  raised.  If  now  from  this  negative  a  fresh 
impression  be  made  by  galvanoplasty,  the  result  will  be  a  true 
copy  of  the  original,  possessing  the  same  sharpness  and  fine- 
ness of  the  contours,  lines  arid  hatching. 

A  true  reproduction  of  plastic  works  of  art  can  in  the  same 
manner  be  made,  but  a  current-conducting  surface  is  required 
for  effecting  the  deposit.  As  seen  above,  for  the  reproduction 
of  a  metallic  original,  two  galvanoplastic  deposits  are  re- 
quired, one  for  the  purpose  of  obtaining  a  negative,  and  the 
other  in  order  to  produce  from  the  negative  the  positive — a 
copy  true  to  the  original. 

Jacobi,  the  inventor  of  galvanoplasty,  already  endeavored 
to  avoid  the  process  of  two  galvanoplastic  deposits  by  making 
an  impression  of  the  original  in  a  plastic  mass  (melted  rosin, 
wax,  or  plaster  of  Paris),  rendering  this  non-metallic  negative 
conductive,  and  depositing  upon  it  copper,  thus  obtaining  a 

true  copy  of  the  original. 

(558) 


GALVANOPLASTY  (REPRODUCTION).  559 

It  is  not  within  the  scope  of  this  work  to  describe  the  various 
phases  through  which  the  art  of  galvanoplasty  has  passed 
since  its  invention.  In  the  historical  part  reference  has  been 
made  to  several  facts,  such  as  making  non-metallic  impressions 
(moulds  or  matrices)  conductive  by  graphite,  a  discovery  for 
which  we  are  indebted  to  Murray,  and  which  was  also  made 
independently  by  Jacobi  ;  further,  the  production  of  moulds 
in  gutta-percha ;  so  that  in  this  chapter  we  have  solely  to  deal 
with  the  present  status  of  galvanoplasty. 

I.     GALVANOPLASTY  IN  COPPER. 

Copper  is  the  most  suitable  metal  for  galvanoplastic  pro- 
cesses, that  which  is  precipitated  by  electrolysis  showing  the 
following  valuable  properties  :  It  can  be  deposited  chemically 
pure,  and  in  this  state  is  less  subject  to  change  than  ordinary 
commercial  copper,  or  the  copper  alloys  in  general  use,  its 
tensile  strength  being  20  per  cent,  greater  than  that  of  smelted 
copper.  Its  hardness  is  also  greater,  while  its  specific  gravity 
(8.85)  lies  between  that  of  cast  and  rolled  copper. 

The  physical  properties  of  copper  deposited  by  electrolysis 
are  dependent  upon  the  condition  of  the  bath,  as  well  as  on 
the  intensity  and  tension  of  the  current.  The  bath  used  for 
depositing  copper  is  in  all  cases,  a  solution  of  copper  sulphate 
(blue  vitriol). 

Smee  proved  by  experiments  that,  with  as  intense  a  current- 
strength  as  possible  without  the  evolution  of  hydrogen,  the 
copper  'is  obtained  as  a  tenacious,  fine-grained  deposit.  But 
when  the  current-strength  is  so  intense  that  hydrogen  is 
liberated,  copper  in  a  sandy,  pulverulent  form  is  obtained, 
and  in  coarsely  crystalline  form  when  the  current-strength  is 
very  slight. 

At  a  more  recent  period,  Hubl  and  Forster  have  instituted 
a  series  of  systematic  experiments  for  the  determination  of  the 
conditions  under  which  deposits  with  different  physical  prop- 
erties are  obtained.  Forster,  in  addition,  deserves  credit  for 
his  investigations  of  the  anodal  solution-processes. 


560  ELECTRO-DEPOSITION    OF    METALS. 

Hiibl  worked  with  5  per  cent,  neutral  and  5  per  cent,  acid 
solutions,  as  well  as  with  20  per  cent,  neutral  and  20  per  cent, 
acid  solutions.  The  neutral  solutions  were  prepared  by  boil- 
ing blue  vitriol  solution  with  carbonate  of  copper  in  excess, 
and  the  acid  solutions  by  adding  2  per  cent,  of  sulphuric  acid 
of  66°  Be.  The  result  was  that  in  the  neutral  5  per  cent,  solu- 
tion less  brittle  deposits  were  obtained  with  a  slight  current- 
density  than  in  a  more  concentrated  solution,  though  the 
appearance  of  the  deposits  was  the  same.  The  experiments 
with  acidulated  baths  confirmed  the  fact  that  free  sulphuric 
acid  promotes  the  formation  of  very  fine-grained  deposits  even 
with  very  slight  current-densities,  and  it  would  seem  that  the 
brittleriess  of  copper  deposited  from  the  acid  baths  is  influ- 
enced less  by  the  concentration  than  by  the  current-density 
used. 

With  the  use  of  high  current-densities,  spongy  deposits  of  a 
dark  color,  but  frequently  also  sandy  deposits  of  a  red  color, 
are  obtained  from  the  neutral  as  well  as  from  acid  blue  vitriol 
solutions.  These  phenomena  are  directly  traceable  to  the 
effect  of  the  hydrogen  reduced  on  the  cathodes. 

However,  such  spongy  deposits  are  also  obtained  with  the 
use  of  slight  current-densities,  when  the  concentration  of  the 
-electrolyte  has  become  less  by  the  exhaustion  of  the  bath  on 
the  cathodes,  and  Mylius  and  Fromm  have  shown  that  copper 
reduced  under  such  conditions  had  absorbed  hydrogen,  while 
Lenz,  in  addition  to  hydrogen,  found  in  a  brittle  copper  de- 
posit, carbonic  oxide  and  carbonic  acid.  Soret  also  found 
carbonic  acid  in  addition  to  hydrogen,  and  attributes  to  it- the 
unfavorable  effect,  while  he  considers  a  content  of  hydrogen 
as  unessential  for  the  mechanical  properties  of  the  electrolytic- 
ally  deposited  copper. 

It  is  impossible  to  understand  where  the  carbonic  acid  is  to 
come  from,  provided  there  has  been  no  contamination  of  the 
electrolyte  by  organic  substances. 


GALVANOPLASTY    (REPRODUCTION).  561 

A.     GALVANOPLASTIC  REPRODUCTION  FOR  GRAPHIC  PURPOSES. 
(ELECTROTYPY.  ) 

The  processes  used  in  galvanoplasty  may  be  arranged  in  two 
classes,  viz.,  the  deposition  of  copper  with,  or  without,  the  use 
of  external  sources  of  current,  the  first  comprising  galvanoplastic 
deposits  produced  by  means  of  the  single-cell  apparatus,  and 
the  other  those  by  the  battery,  thermo-electric  pile,  dynamo 
or  accumulator. 

1.      Galvanoplastic  Deposition  in  the  Cell  Apparatus. 

The  cell  apparatus  consists  of  a  vessel  containing  blue 
vitriol  solution  kept  saturated  by  a  few  crystals  of  blue  vitriol 
placed  in  a  muslin  bag,  or  a  small  perforated  box  of  wood, 
stoneware,  etc.  In  this  vessel  are  placed  round  or  square 
porous  clay  cells  (diaphragms)  which  contain  dilute  sulphuric 
acid  and  a  zinc  plate,  the  zinc  plates  being  connected  with 
each  other  and  with  the  objects  to  be  moulded — which  may 
be  either  metallic  or  made  conductive  by  graphite — by  copper 
wire  or  copper  rods. 

The  objects  to  be  moulded  play  the  same  role  as  the  copper 
electrode  in  the  Daniell  cell,  and  the  cell  apparatus  is  actually 
a  Daniell  cell,  closed  in  itself,  in  which  the  internal,  instead 
of  the  external,  current  is  utilized.  As  soon  as  the  circuit  is 
closed  by  the  contact  of  the  objects  to  be  copied  with  the  zinc 
of  the  porous  cell,  the  electrolytic  process  begins.  The  zinc 
is  oxidized  by  the  oxygen  and  with  the  sulphuric  acid  forms 
zinc  sulphate  (white  vitriol)  while  the  copper  is  reduced  from 
the  blue  vitriol  solution  and  deposited  in  a  homogeneous 
layer  upon  the  objects  to  be  moulded. 

Forms  of  cells.  The  form  and  size  of  the  simple  cell-appa- 
ratus vary  very  much  according  to  the  purpose  for  which  the 
latter  is  to  be  used.  While  formerly  a  horizontal  arrangement 
of  the  objects  to  be  copied  and  of  the  zinc  plates  was  generally 
preferred,  because  with  this  arrangement  the  fluids  show  a  more 
uniform  concentration,  preference  was  later  on  properly  given 
to  the  vertical  arrangement.  Particles  becoming  detached 
36 


562 


ELECTRO-DEPOSITION    OF    METALS. 


FIG.  135. 


from  the  zinc  plates  get  only  too  easily  upon  the  object  to  be 
reproduced  and  cause  holes  in  the  deposit,  while  with  the 
vertical  arrangement  the  progress  of  deposition  can  at  any 
time  be  controlled  by  lifting  out  the  objects  without  taking  the 
apparatus  apart,  as  in  the  case  with  the  horizontal  arrange- 
ment. Hence,  only  such  apparatus  in  which  the  zinc  plates 
and  the  objects  to  be  moulded  are  arranged  vertically  oppo- 
site one  to  the  other  will  here  be  discussed. 

A  simple  apparatus  frequently  used  by  amateurs  for  mould- 
ing metals,  reliefs,  etc.,  is  shown  in  Fig.  135. 

In  a  cylindrical  vessel  of  glass  or  stoneware  filled  with  satu- 
rated blue  vitriol  solution  is  placed  a  porous  clay  cell,  and  in 
the  latter  a  zinc  cylinder  projecting  about  0.039  to  0.79  inch 

above  the  porous  clay  cell.  To 
the  zinc  is  soldered  a  copper 
ring,  as  plainly  shown  in  the 
illustration.  The  clay  cell  is 
filled  with  dilute  sulphuric  acid 
(1  acid  to  30  water),  to  which 
some  amalgamating  salt  may 
be  suitably  added.  The  articles 
to  be  moulded  are  suspended 
to  the  copper  ring,  care  being 
had  to  have  the  surfaces  which 
are  to  be  covered  near  and 
opposite  to  the  cell.  To  sup- 
plement the  content  of  copper, 
small  linen  or  sail-cloth  bags 

filled  with  blue  vitriol  are  attached  to  the  upper  edge  of  the 
vessel. 

Large  apparatus. — To  cover  large  surfaces,  large,  square 
tanks  of  stoneware,  or  wood,  lined  with  lead,  gutta-percha,  or 
another  substance  unacted  upon  by  the  bath  are  used.  For 
baths  up  to  three  feet  long,  stoneware  tanks  are  to  be  preferred. 
Fig.  136  shows  the  French  form  oj  cell  apparatus.  In  the 
middle  of  the  vat,  and  in  the  direction  of  its  length,  is  dis- 


GALVANOPLASTY    (REPRODUCTION). 


563 


posed  a  row  of  cylindrical  cells,  close  to  each  other,  each  pro- 
vided with  its  zinc  cylinder.  A  thin  metallic  ribbon  is  con- 
nected with  all  the  binding  screws  of  the  cylinder,  and  is  in 
contact  at  its  extremities  with  two  metallic  bands  on  the 
ledges  of  the  depositing  vat.  The  metallic  rods  supporting 
the  moulds  are  in  contact  with  the  metallic  bands  of  the 
ledges,  and  therefore,  in  connection  with  the  zincs.  * 

FIG.  136. 


The  German  form  of  cell  apparatus  is  shown  in  Fig.  137. 
It  is  provided  with  long,  narrow,  rectangular  cells  of  a  corres- 
pondingly greater  height  than  the  column  of  fluid. 

Across  the  vat  are  placed  three  conducting  rods  connected 
with  each  other  by  binding  screws  and  copper  wire.  To  the 
center  rod,  which  lies  over  the  cells,  are  suspended  the  zinc 
plates  by  means  of  a  hook,  while  the  outer  two  rods  serve  for 
the  reception  of  the  moulds. 

The  zinc  surfaces  in  the  simple  apparatus  should  be  of  a 
size  about  equal  to  that  of  the  surfaces  to  be  reproduced,  if 
dilute  sulphuric  acid  (1  acid  to  30  water)  is  to  be  used. 


564 


ELECTRO-DEPOSITION    OF    METALS. 


Copper  bath  for  the  cell  apparatus. — This  consists  of  a  solu- 
tion of  41  to  44  Ibs.  of  pure  blue  vitriol  free  from  iron,  for  a 
100-quart  bath,  with  an  addition  of  about  3}  to  4J  Ibs.  of 
sulphuric  acid  of  60°  Be.,  free  from  arsenic. 

It  is  not  customary  to  add  to  the  copper  bath  serving  for 
graphic  purposes  a  larger  quantity  of  sulphuric  acid  than 
that  mentioned  above,  because  acid  diffuses  constantly  from 
the  fluid  in  the  clay  cells  into  the  bath,  thus  gradually  in- 
creasing the  content  of  acid  in  the  latter.  If  the  generation 

FIG.  137. 


of  current  is  induced  by  acidulating  the  water  in  the  clay 
cells,  a  further  addition  of  acid  for  the  cells  would  actually 
not  be  required  for  the  progressive  development  of  the  current, 
since  the  acid-residue  formed  by  the  decomposition  of  the 
blue  vitriol  migrates  from  the  zinc  of  the  cells,  and  brings 
fresh  zinc-ions  into  solution.  A  diffusion  of  acid  from  the 
cells  into  the  bath  would  in  this  manner  be  avoided,  and  only 
the  zinc-sulphate  solution  formed  would  diffuse  into  the 
copper  bath.  It  appears,  however,  that  without  an  occasional 
addition  of  a  small  quantity  of  sulphuric  acid  to  the  cell- 
solution  the  process  of  deposition  runs  its  course  very  slowly, 
which  is  not  desirable  for  the  manufacture  of  cliches. 

It  may  therefore  happen  that  after  working  the  copper  bath 


GALVANOPLASTY  (REPRODUCTION). 


565 


for  a  long  time,  it  contains  too  much  acid,  a  portion  of  which 
has  to  be  removed.  For  this  purpose  the  bath  was  formerly 
mixed  with  whiting,  and  the  gypsum  formed  filtered  off.  This 
method,  however,  cannot  be  recommended,  gypsum  being  not 
entirely  insoluble  in  water,  and  it  is  better  to  replace  it  by 
cupric  carbonate  or  cuprous  oxide  (cupron).  If  cupric  car- 
bonate be  used,  it  is  advisable  thoroughly  to  stir  the  bath,  or 
what  is  better,  to  boil  it,  so  as  to  remove  as  completely  as  pos- 
sible the  carbonic  acid. 

By  the  diffusion  of  zinc  sulphate  solution  from  the  clay 
cells,  the  bath  becomes  gradually  rich  in  zinc  salt,  and  it  will 
be  noticed  that  a  certain  limit — with  a  content  of  about  10  per 
cent,  zinc  sulphate — the  copper  deposits  turn  out  brittle.  The 
bath  has  then  to  be  entirely  renewed. 

The  content  of  copper  in  the  bath  decreases  in  accordance 
with  the  copper  deposited,  and  the  concentration  of  the  bath 
would  consequently  become  so  low  that  useful  deposits  could 
no  longer  be  obtained,  if  care  were  not  taken  to  replace  the 
copper.  This  is  done  by  suspending  perforated  baskets  of 
stoneware  or  lead,  filled  with  blue  vitriol  crystals,  in  the  bath. 

Since  directions  are  frequently  found  in  which  the  blue 
vitriol  solutions  to  be  used  are  given  according  to  their  weights 
by  volume  or  degrees  of  Be.,  a  table  showing  the  content  of 
blue  vitriol  is  given  below. 


Degrees  Be. 

Weight  by  volume. 

This  solution 
contains  crystallized 
blue  vitriol. 

5°    
10°    
12° 

1.035 
1.072 
1  088 

5  per  cent. 
11 
13 

15°    
16°    
17°     .                   
18°    
19°    .... 

1.113 
1.121 
1.130 
1.138 
1.147 

17 
18 
19 
20 
21 

20°    
21° 

1.157 
1  166 

23 

24 

22° 

1  176 

25 

566  ELECTRO-DEPOSITION    OF    METALS. 

Electro-motive  force. — The  effective  electro-motive  force  in 
the  cell  apparatus  amounts  to  about  0.75  volt.  It  may  be 
regulated  by  either  bringing  the  matrices  more  closely  to  the 
diaphragms,  or  removing  them  a  greater  distance  from  them. 
In  the  first  case,  the  resistance  of  the  bath  is  decreased,  the 
current-density  being  consequently  increased,  while  in  the 
other,  the  resistance  of  the  bath  is  increased  and  the  current 
density  decreased. 

For  regulating  the  electro-motive  force  a  rheostat  may  also 
be  placed  in  the  circuit,  between  the  matrices  and  the  zincs, 
instead  of  connecting  them  directly  by  a  copper  wire.  Although 
this  method  is  not  in  vogue,  it  is  certainly  recommend  able. 

For  working  on  a  large  scale,  the  cell  apparatus  is  but  sel- 
dom used,  at  least  not  for  the  production  of  electros.  It  is, 
however,  occasionally  employed  for  the  reproduction  of  ob- 
jects of  art  with  very  high  reliefs,  so  as  to  cover  them  as  uni- 
formly as  possible  and  quite  slowly  with  copper.  The  cell 
is  also  still  liked  for  the  production  of  matrices. 

2.  Galvanoplastic  Deposition  by  the  Battery  and  Dynamo. 

Since  it  has  been  shown  in  the  preceding  section  that  a  cell 
apparatus  is  to  be  considered  as  a  Daniell  cell  closed  in  itself,  it 
will  not  be  difficult  to  comprehend  that  in  economical  respects 
no  advantage  is  offered  by  the  production  of  galvanoplastic 
depositions  by  a  separate  battery,  because  in  both  cases  the 
chemical  work  is  the  same,  and  the  zinc  dissolved  by  the  use 
of  the  Daniell  or  Bunsen  cell  effects  no  greater  quantity  of  cop- 
per deposit  in  the  bath  than  the  same  quantity  of  zinc  dissolved 
in  the  cells  of  the  single  apparatus.  In  other  respects  the  use 
of  a  battery,  however,  offers  great  advantages. 

The  employment  of  an  external  source  of  current  requires 
the  same  arrangement  as  shown  in  Figs.  44  and  45,  pp.  140, 
copper  anodes  being  placed  in  the  bath  and  connected  with 
the  anode  pole  of  the  battery.  Copper  being  dissolved  in  the 
anodes,  the  sulphuric  acid  residue  which  is  liberated  is  satura- 
ted with  blue  vitriol,  the  content  of  copper  being  thus,  if  not 


GALVANOPLASTY    (REPRODUCTION).  567 

entirely,  at  least  approximately,  kept  constant.  Furthermore, 
no  foreign  metallic  salts  reach  the  bath,  as  is  the  case  in  the 
simple  apparatus,  by  zinc  sulphate  solution  penetrating  from 
the  clay  cells  and  causing  the  formation  of  rough  and  brittle 
deposits  of  copper.  With  the  use  of  anodes  of  chemically  pure 
copper  the  bath  will  thus  always  remain  pure. 

The  current  may  also  be  regulated  within  certain  limits  by 
bringing  the  anodes  more  closely  to  the  objects,  or  removing 
them  a  greater  distance  from  them.  The  principal  advantage, 
however,  consists  in  that  by  placing  a  rheostat  in  the  circuit 
the  current  strength  can  be  controlled  as  required  by  the  dif- 
ferent kinds  of  moulds. 

a.  Depositions  with  the  Battery. 

Cells. — The  Daniell  cell  described  on  p.  71,  yields  an 
electro-motive  force  of  about  1  volt,  and  is  much  liked  for  this 
purpose.  Since  the  copper  bath  for  galvanoplastic  purposes 
requires  for  its  decomposition  an  electro-motive  force  of  only 
0.5  to  1  volt,  it  will  be  best  for  slightly  depressed  moulds  to 
couple  the  elements  for  quantity  (Fig.  19,  p.  89)  alongside  of 
each  other ;  and  only  in  cases  where  the  particular  kind  of 
moulds  requires  a  current  of  greater  electro-motive  force  to 
couple  two  cells  for  electro-motive  force  one  after  the  other,  an 
excess  of  current  being  rendered  harmless  by  means  of  the 
rheostat,  or  by  suspending  larger  surfaces. 

Bunsen  or  Meidinger  cells  may,  however,  be  used  to  great 
advantage,  since  the  zincs  of  the  Daniell  cells  become  tarnished 
with  copper,  and  have  to  be  frequently  cleansed  if  the  process 
is  not  to  be  retarded  or  entirely  interrupted.  The  Bunsen 
cells  need  only  be  coupled  for  quantity,  their  electro-motive 
force  being  considerably  greater.  To  be  sure,  the  running 
expenses  are  much  greater  than  with  Daniell  cells,  at  least 
when  nitric  acid  is  used  for  filling.  The  lasting  constancy  of 
the  Meidinger  cells  would  actually  make  them  the  most  suit- 
able of  all  for  continuous  working,  but  by  reason  of  their 
slight  current  strength  a  large  number  of  them  would  have 
to  be  used. 


568  ELECTRO-DEPOSITION    OP    METALS. 

All  that  has  been  said  under  "  Installations  with  Cells,"  p. 
132,  in  regard  to  conducting  the  current,  rheostats,  conduct- 
ing rods,  anodes,  etc.,  applies  also  to  plants  for  the  galvano- 
plastic  deposition  of  copper  with  batteries. 

b.  Depositions  with  the  Dynamo. 

The  improvements  in  dynamos  have  also  benefited  indus- 
trial galvanoplasy,  and  problems  can  now  be  solved  in  a  much 
shorter  time  and  with  much  greater  ease  than  in  a  cell  appa- 
ratus, without  having  to  put  up  with  the  obnoxious  vapors 
which  make  themselves  very  disagreeably  felt  in  working  on 
a  large  scale  with  a  simple  apparatus.  That  the  use  of  a 
dynamo  offers  decided  advantages  is  best  proved  by  the  fact 
that  no  galvanoplastic  plant  of  any  importance  works  at 
present  without  one,  and  there  can  scarcely  be  any  doubt  that 
establishments  which  still  work  exclusively  with  the  simple 
apparatus  will  be  forced  to  make  use  of  a  dynamo,  if  they 
wish  to  keep  up  with  competition  as  regards  cheapness  and 
rapidity  of  work. 

Dynamos. — It  is  best  to  use  a  dynamo  capable  of  yielding  a 
large  quantity  of  current  with  an  impressed  electro-motive 
force  of  2.  or,  at  the  utmost,  3  volts,  in  case  it  is  not  to  serve 
for  rapid  galvanoplasty;  for  the  latter  a  machine  of  5  to  10  volts 
impressed  electro-motive  force  is  required.  For  the  old,  slow 
process,  by  which  deposits  for  graphic  purposes  are  produced 
in  5  to  6  hours,  an  impressed  electro-motive  force  of  2  volts 
suffices  for  baths  coupled  in  parallel.  If,  however,  there  are  to 
be  charged  from  the  dynamo  one  or  more  accumulator  cells, 
which  are  to  furnish  current  to  the  bath  while  the  steam  engine 
is  not  running  during  the  intermission  of  work,  or  to  finish 
deposits  after  working  hours,  the  impressed  electro-motive 
force,  with  cells  coupled  in  parallel,  must  be  3  volts,  and  with 
cells  coupled  in  series  in  proportion  to  their  number. 

It  may  also  happen  that  in  a  galvanoplastic  plant  currents 
of  greatly  varying  electro-motive  force  may  be  required  for 
depositions.  For  depositing  copper  according  to  the  old  pro- 


GALVANOPLASTY  (REPRODUCTION). 


569 


cess  there  should,  for  instance,  be  available  a  large  current- 
strength  with  only  1  to  1.5  volts,  while  for  a  rapid  galvano- 
plastic  bath  a  current  of  6  volts  is  at  the  same  time  to  be  used. 
If  a  dynamo  of  6  volts  impressed  electro-motive  force  were  to 
be  used,  the  excess  of  electro-motive  force  would  have  to  be 
destroyed  by  rheostats  in  front  of  the  baths  requiring  a  slight 
electro-motive  force,  in  case  it  is  not  convenient  to  couple 
these  baths  in  series  (see  later  on).  The  destruction  of  electro- 
motive force  is,  however,  not  economical,  and,  in  such  a  case, 
the  use  of  two  dynamos  with  different  electro-motive  forces  is 
advisable.  It  is  best  to  combine  both  dynamos  with  a  motor- 
generator,  if  the  plant  is  connected  with  a  power  circuit  of  a 

FIG.  138. 


central  station,  the  construction  being  such  that  the  dynamo 
which  is  perhaps  only  temporarily  in  use  can  be  readily 
disengaged. 

Fig.  138  shows  such  a  double  aggregate,  built  by  the  firm 
of  Dr.  G.  Langbein  &  Co.  for  the  German  Imperial  Printing 
Office.  The  larger  dynamo  has  a  capacity  of  1000  amperes 
and  2.5  volts,  and  the  smaller  one,  one  of  250  amperes  and 
6  volts. 

Current-conductors  of  sufficient  thickness,  corresponding  to 
the  quantities  of  current  have  to  be  provided  to  prevent  loss 
of  current  by  resistance  in  the  conductors.  To  avoid  repetir 


570  ELECTRO-DEPOSITION    OF    METALS. 

tion,  we  refer  to  what  has  been  said  on  this  subject  under 
"  Arrangement  of  Electro-plating  Establishments,"  the  direc- 
tions there  given  applying  also  to  the  galvanoplastic  process. 

Coupling  the  baths. — When  coupling  the  baths  in  parallel, 
each  bath  will  have  to  be  provided  with  a  rheostat  and  am- 
meter, while  a  voltmeter  with  a  voltmeter  switch  may  be  em- 
ployed in  common  for  several  baths.  If  the  baths  are  of 
exactly  the  same  composition  and  the  same  electrode-distances 
are  maintained  in  them,  regulation  of  the  current  by  the 
shunt  rheostat  of  the  dynamo  will  suffice. 

Coupling  the  baths  in  series  may  under  certain  conditions 
be  of  advantage.  In  such  a  case,  a  dynamo  of  adequately 
higher  electro-motive  force  will  of  course  have  to  be  employed. 

With  the  baths  coupled  in  se.ries  the  cathode  (object)  sur- 
faces in  all  the  baths  should  be  of  the  same  size,  or  at  least 
approximately  so.  The  baths  are  coupled  in  series  by  con- 
necting the  anodes  of  the  first  bath  with  the  -f-  pole  of  the 
dynamo,  the  cathodes  of  the  first  bath  with  the  anodes  of  the 
second,  the  cathodes  of  the  second  with  the  anodes  of  the  third, 
and  so  on,  and  reconducting  the  current  from  the  cathodes  of 
the  last  bath  to  the  —  pole  of  the  dynamo  (Fig.  64). 

With  this  simple  coupling  in  series,  the  impressed  electro- 
motive force  is  uniformly  distributed  in  all  the  baths,  so  that 
with  four  baths  coupled  in  series,  and  an  impressed  electro- 
motive force  of  4  volts,  an  electro-motive  force  of  1  volt  is  pre- 
sent in  each  bath  if  the  conductivity  resistance  be  left  out  of 
consideration.  Hence,  it  may  be  readily  calculated  how  many 
baths  have  to  be  coupled  in  series  to  utilize  a  given  impressed 
electro-motive  force,  when  the  electro-motive  force  required  for 
one  bath  is  known. 

If,  for  instance,  there  is  a  dynamo  with  6  volts  impressed 
electro-motive  force,  and  the  electro-motive  force  required  for 
one  bath  is  1.5  volts,  then  4  baths  have  to  be  coupled  in  series, 
since  they  require  1.5  X  4  =  6  volts.  If,  however,  only  one 
volt  is  required  for  one  bath,  then  6  baths  will  have  to  be 
coupled  in  series,  or,  in  case  fewer  baths  are  to  be  used,  the 


GALVANOPLASTY  (REPRODUCTION). 


571 


impressed  electro-motive  force  of  the  dynamo  has  to  be  suitably 
regulated  by  the  shunt  rheostat. 

Besides,  the  simple  coupling  in  series,  mixed  coupling,  also 
called  coupling  in  groups,  a  combination  of  coupling  in  parallel 
and  in  series,  may  be  employed.  This  is  effected  by  combin- 
ing a  number  of  baths  to  a  group  in  parallel,  and  coupling 
several  such  groups  in  series. 

FIG.  139. 


fptt. 


f 

r 

r 

RHEOSTA 

•Ai- 

In  large  galvanoplastic  plants  the  advantages  derived  from 
this  mixed  coupling  are  as  follows : 

With  the  simple  couple  in  series,  the  electrode-surfaces  in 
all  the  baths  must  be  of  the  same  size.  When  finished  objects 
are  taken  from  a  bath,  the  current  conditions  are  changed, 
until  in  place  of  the  object  taken  out  fresh  surfaces  of  the  same 
size  are  suspended  in  the  bath,  and  as  this  cannot  always  be 
immediately  done,  irregularities  in  working  will  result.  If, 
however,  the  baths  be  combined  in  groups  in  the  manner 
shown  in  Fig.  139,  only  the  cathode-surfaces  of  each  of  the 
groups  coupled  in  parallel,  need  to  be  of  the  same  size,  or  ap- 
proximately so,  and  with  the  observation  of  this  condition  it 


572  ELECTRO-DEPOSITION    OF    METALS. 

is  entirely  indifferent  whether  a  bath  of  one  group  is  not  at 
all  charged  with  cathodes. 

For  the  adjustment  of  any  difference  in  the  electro-motive 
force  in  the  baths  of  the  separate  groups,  it  is  advisable  to 
place  in  each  bath  a  rheostat  in  shunt. 

While  with  baths  coupled  iif  parallel,  the  electro-motive 
force  of  the  dynamo  corresponds  to  the  requisite  electro- motive 
force  of  one  bath,  but  the  current-strength  is  calculated  from 
the  sum  of  all  the  cathodes  present  in  the  different  baths, 
with  baths  coupled  in  series  only  the  total  cathode  surface  of 
one  bath  is  decisive  as  regards  the  current-strength,  the  electro- 
motive force  of  the  machine  resulting  from  the  sum  of  the 
electro-motive  forces  of  the  separate  baths.  With  baths 
coupled  in  groups  the  requisite  impressed  electro-motive  'force 
is  calculated  from  the  number  of  groups  of  baths  coupled  in 
series,  but  the  current-strength  from  the  total  cathode-surface 
of  only  one  group. 

The  following  examples  may  serve  as  illustrations  :  Suppose 
3  baths,  each  with  100  square  decimeters  cathode-surface,  are 
coupled  in  parallel,  and  the  electro-motive  force  for  one  bath 
is  1.5  volts.  Hence  in  the  three  baths  there  are  100  X  3  = 
300  square  decimeters  cathode  surface,  and  if,  for  instance,  one 
square  decimeter  requires  2  amperes,  then  the  3  baths  require 
300  X  2  =  600  amperes.  Thus  the  capacity  of  the  dynamo 
must  be  600  amperes,  with  an  impressed  electro-motive  force 
of  1.5  volts,  but  for  practical  reasons  a  machine  of  2  volts 
should  be  selected. 

Suppose  4  baths,  each  charged  with  100  square  decimeters 
cathode- surface,  are  coupled  in  series,  and  the  bath  electro- 
motive force  is  1.25  volts,  and  the  current-density  2  amperes. 
Hence  there  will  be  required,  100  X  2  =  200  amperes,  and 
1.25  X  4  =  5  volts. 

Suppose  9  baths  are  coupled,  mixed  in  three  groups  of  3 
baths  each,  the  latter  being  coupled  in  parallel,  and  the  three 
groups  coupled  in  series.  Now  if  each  group  be  charged  with 
300  square  decimeters  cathode-surface  and  the  bath  electro- 


GALVANOPLASTY  (REPRODUCTION).  573 

motive  force  be  also  1.25  volts  and  the  current-density  2  am- 
peres, then  there  will  be  required,  300  X  2  =  600  amperes, 
and  1.25  X  3  =  3.75  volts,  or  practically,  4  volts  impressed 
electro-motive  force. 

c.   Combined  Operation  with  Dynamo  and  Accumulators. 

When,  as  is  frequently  the  case  in  galvanoplastic  plants 
working  with  the  slow  process  of  deposition,  electrotypes  have 
to  be  finished  in  a  hurry,  recourse  has  to  be  had  to  night 
work.  If  the  dynamo  is  not  driven  by  a  motor-generator  fed 
from  a  power  circuit  of  a  central  station,  it  will  be  necessary 
to  use  for  night  work  either  a  cell  apparatus,  or  to  feed  the 
bath  from  accumulators. 

An  interruption  in  the  galvanoplastic  deposition  of  copper 
is  a  great  drawback,  because  an  additional  deposit  made  after 
the  current  has  been  interrupted  adheres  badly  upon  the  one 
previously  made,  as  blisters  are  readily  formed,  or  the  deposit 
peels  off.  The  chief  object  in  the  use  of  an  accumulator  is 
that  it  allows  of  the  work  being  carried  on  during  the  noon 
hour  when  the  steam  engine  is  generally  stopped,  and  of  fin- 
ishing matrices  which  are  suspended  late  in  the  afternoon, 
after  working  hours. 

In  order  to  avoid  repetition,  the  reader  is  referred  to  what 
has  been  said  on  p.  184  et  seq.,  in  regard  to  the  use  of  an  ac- 
cumulator in  addition  to  the  dynamo. 

For  galvanoplasty  in  copper  by  the  slow  process,  one  accu- 
mulator cell  of  sufficient  capacity  to  supply  current  for  2  or  3 
hours  is,  as  a  rule,  all  that  is  required.  This  cell  is  charged 
from  the  dynamo  at  the  same  time,  while  the  latter  directly 
operates  the  bath,  a  machine  with  an  impressed  electro-motive 
force  of  3  volts  being  required  for  the  purpose. 

If  several  cells  have  to  be  used,  it  has  to  be  decided  accord- 
ing to  the  capacity  of  the  dynamo,  whether  they  are  to  be 
charged  in  parallel  or  in  series.  If  great  demands  are  for  a 
longer  time  made  on  the  accumulators,  it  is  advisable  to  use  a 
separate  dynamo  for  charging  purposes. 


574  ELECTRO-DEPOSITION    OF    METALS. 

Copper  baths  for  galvanoplastic  depositions  with  a  separate 
source  of  current. — The  directions  for  the  composition  of  the 
bath  vary  very  much,  some  authors  recommending  a  copper 
solution  of  18°  Be.,  which  is  brought  up  to  22°  Be.  by  the 
addition  of  pure  concentrated  sulphuric  acid.  Others  again 
increase  the  specific  gravity  of  the*  bath  up  to  25°  Be.  by  the 
addition  of  sulphuric  acid,  while  some  prescribe  an  addition 
of  3  to  7  per  cent,  of  sulphuric  acid. 

It  is  difficult  to  give  a  general  formula  suitable  for  all  cases, 
because  the  addition  of  sulphuric  acid  will  vary  according  to 
the  current-strength  available,  the  nature  of  the  moujds,  and 
the  distance  of  the  anodes  from  the  objects.  The  object  of 
adding  sulphuric  acid  is,  on  the  one  hand,  to  render  the  bath 
more  conductive  and,  when  used  in  proper  proportions,  to 
make  the  deposit  more  elastic  and  smoother,  and  prevent-the 
brittleness  and  coarse-grained  structure  which,  under  certain 
conditions,  appear. 

However,  it  is  also  the  function  of  the  sulphuric  acid  to 
prevent  the  primary  decomposition  of  the  blue  vitriol,  and  to 
effect  in  a  secondary  manner  the  reduction  of  the  copper.  As 
has  been  explained  on  p.  50,  acids,  bases  and  salts  dissociate 
in  aqueous  solution,  and  only  substances  which  dissociate 
in  aqueous  solution  are  conductors  of  the  electric  current, 
they  being  the  better  conductors,  the  greater  their  power  of 
dissociation  is.  The  dilute  sulphuric  acid  being  much  more 
dissociated,  takes  charge  in  a  much  higher  degree  of  con- 
ducting the  current  than  the  less  strongly  dissociated  blue 
vitriol  solution.  Consequently  the  cation  of  the  sulphuric 
acid — the  hydrogen-ions — migrates  to  the  cathode,  and  effects 
the  decomposition  of  the  blue  vitriol,  an  equivalent  quantity 
of  copper  being  reduced  upon  the  cathode. 

The  addition  of  a  large  quantity  of  sulphuric  acid,  as  recom- 
mended by  some  authors,  cannot  be  approved,  it  having  been 
found  of  advantage  only  in  a  few  cases. 

For  depositing  with  a  battery,  somewhat  more  sulphuric 
acid  may  for  economical  reasons  be  added  to  the  bath  than 


GALVANOPLASTY  (REPRODUCTION).  575 

when  working  with  the  current  of  a  dynamo.  The  following 
composition  has  in  most  cases  been  found  very  suitable  for  the 
reproduction  of  shallow,  as  well  as  of  deep,  moulds  : 

Blue  vitriol  solution  of  19J°  Be.  100  quarts,  sulphuric  acid 
of  66°  Be.  free  from  arsenic  4|  to  6J  Ibs. 

The  bath  is  prepared  as  follows :  Dissolve  48J  Ibs.  of  blue 
vitriol  in  pure  warm  water,  and,  to  avoid  spurting,  add  gradu- 
ally, stirring  constantly,  the  sulphuric  acid.  At  the  normal 
temperature  of  59°  F.  the  bath  may  be  worked  with  a  current- 
density  of  up  to  2  amperes,  and  if  the  bath  be  agitated,  the 
current-density  may  be  up  to  3  amperes. 

Properties  of  the  deposited  copper. — As  regards  elasticity, 
strength  and  hardness  of  galvanoplastic  copper  deposits,  Hubl 
determined  that  copper  of  great  tenacity,  but  possessing  less 
hardness  and  strength,  is  deposited  from  a  20  per  cent,  solu- 
tion with  the  use  of  a  current-density  of  2  to  3  amperes. 

For  copper  printing  plates  a  20  per  cent,  solution  compounded 
with  3  per  cent,  sulphuric  acid,  and  current-density  of  1.3 
amperes  was  found  most  suitable  by  Giesecke.  Dissolve  for 
this  purpose  50.6  Ibs.  of  blue  vitriol  for  a  100-quart  bath  and 
add  6.6  Ibs.  of  sulphuric  acid. 

Forster  and  Seidel  have  shown  that  the  mechanical  proper- 
ties of  the  copper  are  materially  influenced  by  the  temperature 
of  the  electrolyte.  From  Forster's  investigations,  with  a 
cathodal  current-density  of  1  ampere  in  an  electrolyte  com- 
posed of  150  grammes  blue  vitriol  and  50  grammes  sulphuric 
acid  per  liter,  it  appears  that  the  copper  obtained  with  the 
electrolyte  at  140°  F.,  showed  the  greatest  tenacity,  it  decreas- 
ing again  at  a  higher  temperature  while  the  strength  slightly 
increased. 

The  nature,  i.  e.,  the  composition,  of  the  electrolyte  also 
exerts  an  influence  upon  the  structure  of  the  deposit.  Forster 
compounded  the  electrolyte  previously  used  with  a  quantity 
of  sodium  sulphate  equivalent  to  that  of  the  blue  vitriol. 
The  result  showed  that  the  strength  as  well  as  the  tenacity 
was  unfavorably  influenced  at  a  higher  temperature. 


576  ELECTRO-DEPOSITION    OF    METALS. 

Current  conditions. — In  order  to  obtain  a  dense,  coherent 
and  elastic  deposit  in  the  acid  copper  bath,  it  is  first  of  all 
necessary  to  bring  the  current-strength  into  the  proper  pro- 
portion to  the  deposition-surface,  this  applying  to  depositions 
in  the  simple  apparatus,  as  well  as  to  that  produced  with  an 
external  source  of  current. 

The  stronger  the  sulphuric  acid  in  the  clay  cells  of  the 
simple  apparatus  is,  the  more  rapidly  is  the  copper  precipi- 
tated upon  the  moulds.  If  the  zinc-surfaces  of  the  clay  cells 
are  very  large  in  proportion  to  the  surfaces  of  the  moulds, 
the  deposition  of  copper  also  takes  place  more  rapidly.  The 
rapid  reduction  of  copper,  however,  must  above  all  be  avoided 
if  deposits  of  desirable  qualities  are  to  be  obtained,  because  a 
deposit  of  copper  forced  too  rapidly  turns  out  incoherent, 
spongy,  frequently  full  of  blisters  and,  with  a  very  strong 
current,  even  pulverulent. 

The  color  of  the  deposit  is  to  some  extent  a  criterion  of  its 
quality,  a  red-brown  color  indicating  an  unsuitable  deposit, 
while  a  good,  useful  one  may  be  counted  upon  when  it  shows 
a  beautiful  rose  color. 

For  filling  the  clay  cells,  it  has  previously  been  stated  that 
the  acid  is  to  be  diluted  in  the  proportions  of  1  part  of  concen- 
trated sulphuric  acid  of  66°  Be.  to  30  parts  of  water,  the  zinc 
surface  being  supposed  to  be  of  about  the  same  size  as  the  ma- 
trix-surface. If  the  zinc-surface  should  be  smaller,  stronger 
acid  may  be  used,  and  if  it  be  larger,  the  acid  may  be  more 
dilute.  The  proper  concentration  of  the  acid  in  the  clay  cells 
is  readily  ascertained  from  the  progressive  result  of  the  deposit 
and  its  color. 

What  has  been  said  in  reference  to  the  current-strength  ap- 
plies also  to  the  deposition  of  copper  with  a  separate  source  of 
current  (battery  or  dynamo).  The  current-strength  must  be  so 
adjusted  by  means  of  a  rheostat  as  to  allow  of  comparatively 
rapid  deposition  without  detriment  to  the  quality  of  the  de- 
posit. 

According  to  the  composition  of  the  bath,  a  fixed  minimum 


GALVANOPLAhTY  (REPRODUCTION). 


577 


and  maximum  current-density  corresponds  to  it,  which  must 
not  be  exceeded  if  serviceable  deposits  are  to  be  obtained. 
There  is,  however,  a  further  difference  according  to  whether 
the  bath  is  at  rest  or  agitated.  Hiibl  obtained  the  following 
results  : 


Blue  vitriol  solution. 

Minimum  and  maximum  current-density 
per  15.5  square  inches. 

With  solution  at 
rest. 
Ampdres. 

With  solution  gently 
agitated. 
Amperes. 

15  per  cent,  blue  vitriol,  without 
sulphuric  acid  ... 
15  per  cent,  blue  vitriol,   with  6 
per  cent,  sulphuric  acid 
20  per  cent,  blue  vitriol,  without 
sulphuric  acid 
20  per  cent,   blue  vitriol,  with  6 
per  cent,  sulphuric  acid  .... 

2.6  to  3.9 
1.5  "  2.3 
3.4  "  5.1 
2.0  "  3.0 

3.9  to  5.2 
2.3  "  3.0 
5.1  "  6.8 
3.0  "  4.0 

Touching  the  addition  of  sulphuric  acid,  it  was  shown  that 
no  difference  in  the  texture  of  the  deposit  is  perceptible  if  the 
addition  of  acid  varies  between  2  and  8  per  cent. 

The  most  suitable  current-density  for  the  production  of  good 
deposits  with  a  bath  of  the  composition  given  on  p.  575,  when 
at  rest,  is  for  slow  deposition  1  to  2  amperes  per  square  deci- 
meter of  matrix  surface,  and  when  the  bath  is  agitated  2  to  3 
amperes.  The  current-densities  for  rapid  galvanoplastic  baths 
will  be  given  later  on. 

Since  for  ordinary,  strongly  acid  copper  baths  an  electro- 
motive of  |,  to  at  the  utmost  1 J,  volts  is  required,  the  more 
powerful  Bunsen  cells  will  have  to  be  coupled  alongside  each 
other,  while  of  the  weaker  Daniell  or  Lallande  cells,  two,  or  of 
the  Meidinger  cells,  three,  will  have  to  be  coupled  one  after 
the  other,  and  enough  of  such  groups  have  to  be  combined  to 
make  their  active  zinc-surfaces  of  nearly  the  same  size  as  the 
surfaces  of  the  matrices.  However,  for  strongly  acid  baths 
37 


578  ELECTRO-DEPOSITION    OF    METALS. 

coupling  the  separate  weaker  cells  alongside  each  other  also 
suffices. 

When  all  parts  of  the  matrices,  as  well  as  the  deeper  por- 
tions, are  covered  with  copper,  the  current  is  weakened  in  case 
a  deposit  of  a  pulverulent  or  coarse-grained  structure  appears 
on  the  edges  of  the  moulds,  and  it  is  feaned  that  the  deposit 
upon  the  design  or  type  might  also  turn  out  pulverulent. 
The  current  need  not  be  weakened  more  than  is  necessary  to 
prevent  the  dark  deposits  on  the  edges  from  progressing  further 
towards  the  interior  of  the  mould-surfaces.  If,  by  reason  of 
too  strong  a  current,  pulverulent  copper  has  already  deposited 
upon  the  design  or  type,  and  the  fact  is  noticed  in  time  and 
the  current  suitably  weakened,  the  deposit  can  generally  be 
saved  by  the  layers  being  cemented  together  by  the  copper 
which  is  coherently  deposited  with  the  weaker  current. 

In  depositing  with  the  dynamo,  the  current-density  and 
electro-motive  force  have  to  be  properly  regulated  by  means 
of  a  rheostat. 

Brittle  copper  deposits  may  be  caused,  not  only  by  an  unsuit- 
able composition  of  the  electrolyte,  improper  current-densities 
and  impure  anodes  (see  later  on),  but  also  by  contamination 
of  the  bath  with  non-metallic  substances,  certain  organic  sub- 
stances especially  having  an  unfavorable  effect  upon  the  prop- 
erties of  the  copper  deposit. 

Forster  found  the  use  of  hooks  coated  with  rubber  solution 
in  benzol  for  suspending  the  cathodes  a  protection  against  the 
attacks  of  the  electrolyte  and  the  air,  and  smooth  copper  de- 
posits of  a  beautiful  velvety  appearance  were  obtained,  but 
they  were  so  brittle  that  they  could  not  be  detached  without 
breaking  from  the  basis.  The  deposit  contained  small  quan- 
tities of  carbonaceous  substances,  which  could  have  been  de- 
rived only  from  a  partial  solution  of  the  rubber. 

Hubl  also  describes  the  fact  of  having  obtained  brittle  cop- 
per by  the  electrolyte  having  been  contaminated  by  a  small 
quantity  of  gelatine  which  had  passed  into  solution  in  the 
preparation  of  an  electrotype  upon  heliographic  gelatine  reliefs. 


GALVANOPLASTY  (REPRODUCTION).  579 

Dr.  Langbein  had  frequently  occasion  to  notice  that  baths  in 
tanks  lined  with  lead,  and  provided  with  a  coat  of  asphalt  and 
mastic  dissolved  in  benzol,  yielded  brittle  copper  when  the 
coat  of  lacquer  was  not  perfectly  hard,  and  it  was  observed 
that  by  reason  of  an  accidental  contamination  of  the  electro- 
lyte with  gelatine,  deposits  were  formed  which  showed  the 
branched  formation  of  crystals  similar  to  an  arbor  Batumi, 
and  were  extremely  brittle. 

Erich  Miiller  and  P.  Behntje  *  have  recently  investigated 
the  effects  of  such  organic  additions  (colloids)  on  blue  vitriol 
solutions,  additions  of  gelatine,  egg  albumen,  gum,  and  starch 
being  drawn  upon  for  comparing  the  effects.  After  an  elec- 
trolysis for  15  hours,  the  deposits  obtained  from  baths  com- 
pounded with  gum  and  starch  solutions  showed  no  material 
difference  in  appearance  from  deposits  obtained  with  the  same 
current-strength  from  pure  acidulated  blue  vitriol  solution. 
Deposits  obtained  from  baths  to  which  gelatine  and  egg 
albumen  had  been  added,  however,  had  lustrous  streaks  run- 
ning from  top  to  bottom.  The  weight  of  these  deposits  was, 
moreover,  greater  than  that  of  the  copper  obtained  from  pure 
solution,  and  the  presence  of  gelatine  in  the  deposit  could  be 
established  by  analysis.  Further  experiments  proved  that 
the  above-mentioned  phenomena  were  dependent  on  the 
current-density,  and  with  smaller  additions  of  gelatine,  and 
3.5  amperes,  thoroughly  homogeneous,  mirror-bright  copper 
coatings  could  be  obtained,  thus  rendering  it  possible  to  pro- 
duce, by  an  addition  of  gelatine,  a  lustrous  coppering  from 
acid  copper  baths.  The  properties  of  this  copper  are,  however 
such  as  are  not  desirable  for  galvanoplastic  purposes. 

It  is  therefore  absolutely  necessary  to  exclude  such  organic 
substances,  even  if  only  dissolved  in  traces,  from  contact  with 
the  electrolyte. 

.Duration  of  deposition. — The  time  required  for  the  produc- 
tion of  a  deposit  entirely  depends,  according  to  what  has  been 

*  Zeitschrift  fur  Elektrochemie,  XII,  317. 


580 


ELECTRO-DEPOSITION    OF    METALS. 


said  on  p.  124,  on  the  current-density  used.  One  ampere  de- 
posits in.  one  hour  1.18  grammes  of  copper,  and  from  this, 
when  the  current-density  is  known,  the  thickness  acquired  by 
the  deposit  in  a  certain  time  can  be  readily  calculated. 

A  square  decimeter  of  copper,  1  millimeter  thick,  weighs 
about  89  grammes,  and  to  produce  this  weight  with  \  ampere 
current-density,  there  are  required  $£££  =  75  hours.  By  tak- 
ing the  thickness  of  a  deposit  as  0.18  millimeter,  which  suf- 
fices for  all  purposes  of  the  graphic  industry,  then  1  square 
decimeter  will  weigh  89  X  0.18  =  16.02  grammes,  and  for 
their  deposition  with  1  ampere  current-density  will  be  re-' 
quired,  in  round  numbers,  ^nr  =  13  J  hours. 

Below  is  given  the  duration  of  deposition  for  electrotypes 
0.18  millimeter  thick  with  different  current-densities,  and  in 
addition  the  time  is  stated  which  would  be  required  for  the 
formation  of  a  deposit  1  millimeter  thick,  so  that  the  calcula- 
tion of  the  time  required  for  depositing  a  copper  film  of  a 
thickness  different  from  0.18  millimeter  can  be  readily  made 
by  multiplying  the  number  of  hours  in  the  third  column  by 
the  desired  thickness  of  the  copper. 


With  a  current-density  of 

Duration  of  deposition  for 
0.18  millimeter  thick- 
ness of  copper 

A  deposit  of  1  millimeter 
thickness  requires 

0.5    ampere 

27     hours 

150£    hours 

0.75 

18 

101- 

1.0 

' 

13* 

75 

1.5 

9 

, 

50 

2  0 

k 

6f 

37^ 

2.5 

t 

6* 

30 

3.0 

* 

4^ 

25 

4.0 

' 

3| 

18* 

5.0 

1 

2f 

15 

6.0 

t 

2J 

12$ 

7.0 

' 

2 

10f 

8.0 

]T7_ 

Q  ^ 

9.0 

1* 

8i 

Nitrate  baths. — To  shorten  the  duration  of  deposition,  baths 


GALVANOPLASTY  (REPRODUCTION).  581 

have  been  recommended  which,  in  place  ot  blue  vitriol,  are 
prepared  with  cupric  nitrate,  and  which  by  reason  of  being 
more  concentrated  will  bear  working  with  greater  current- 
densities.  To  further  increase  their  conducting  power,  ammo- 
nium chloride  is  added.  Independent  of  the  fact  that  de- 
posits obtained  in  these  baths  are  inferior  in  quality  to  those 
produced  in  blue  vitriol  baths,  such  baths  require  frequent 
corrections,  they  becoming  readily  alkaline  in  consequence  of 
the  formation  of  ammonia.  Besides,  in  view  of  the  short 
time  required  for  deposition  by  the  rapid  galvanoplastic  pro- 
cess, there  is  no  necessity  for  nitrate  baths. 

Agitation  of  the  baths. — From  Hiibl's  table  it  will  be  seen 
that  a  copper  bath  in  motion  can  bear  considerably  higher 
current-densities,  and  hence  will  work  more  rapidly  than  a 
bath  at  rest.  In  electrolytically  refining  copper  it  was  found 
that,  if  the  process  of  reducing  the  copper  is  to  proceed  in  an 
unexceptional  manner,  the  bath  must  be  kept  entirely  homo- 
geneous in  all  its  parts.  When  a  copper  bath  is  at  rest,  and 
the  operation  of  deposition  is  in  progress,  the  following  pro- 
cess takes  place  :  The  layers  of  fluid  on  the  anodes  having  by 
the  solution  of  copper  become  specifically  heavier,  have  a 
tendency  to  sink  down,  while  layers  of  fluid  which  have  be- 
come poorer  in  copper,  and  consequently  specifically  lighter, 
rise  on  the  cathodes  to  the  surface.  These  layers  contain 
more  sulphuric  acid  than  the  lower  ones,  hence  their  resist- 
ance is  slighter  and  their  conducting  power  greater,  the  latter 
being  still  further  increased  by  the  layers  heated  by  the  cur- 
rent also  rising  to  the  surface.  In  consequence  of  this  process 
there  will  be  a  variable  growth  in  thickness  of  the  deposit, 
and  various  phenomena  may  appear  which,  according  to  the 
composition  of  the  layers  in  question,  can  be  theoretically 
established.  If  the  intermixture  of  the  electrolyte  has  not 
progressed  to  any  great  extent,  and  thus  there  are  no  great 
differences,  as  regards  composition,  between  the  upper  and 
lower  layers  of  the  fluid,  the  deposit  will  be  quite  uniformly 
formed  upon  the  lower  as  well  as  upon  the  upper  portions  of 


582  ELECTRO-DEPOSITION    OF    METALS. 

the  cathodes,  although  it  will  be  somewhat  thicker  on  the 
lower  portions,  which  dip  into  the  more  concentrated  copper 
solution,  than  on  the  upper  portions.  This  difference  in 
thickness  in  favor  of  the  lower  cathode-surfaces  will  become 
more  pronounced  as  the  concentration  of  the  lower  layers  of 
the  fluid  increases,  while  the  growth  in  thickness  on  the  upper 
cathode-surface  is  kept  back.  The  concentration  of  the  upper 
layers  of  fluid  may  finally  happen  to  become  so  slight  that  the 
hydrogen-ions  do  not  meet  with  sufficient  blue  vitriol  for  de- 
composition, and  hydrogen  will  consequently  be  separated 
and  the  formation  of  a  sandy  or  spongy  deposit  noticed. 

It  may,  however,  also  happen  that  a  current  of  slight  electro- 
motive force  cannot  overcome  the  greater  resistance  of  the 
more  concentrated  lower  layers  of  fluid,  and  in  consequence 
passes  almost  exclusively  through  the  upper  layers.  So  long 
as  the  hydrogen-ions  find  sufficient  blue  vitriol  and  the  cur- 
rent-density is  slight,  the  growth  of  the  deposit  on  the  upper 
cathode-surfaces  may,  in  this  case,  progress,  while  it  comes  to 
a  stand-still  on  the  lower  ones. 

Experiments  by  Sand  *  have  shown  that  in  consequence  of 
local  exhaustion  of  blue  vitriol  in  an  acid  copper  bath  more 
than  60  per  cent,  of  the  current  is,  notwithstanding  natural 
diffusion,  consumed  for  the  evolution  of  hydrogen.  The  pro- 
duction of  serviceable  deposits  under  such  conditions  is  of 
course  impossible. 

By  constant  agitation  of  the  bath,  the  layers  poorer  in  metal, 
which  have  deposited  copper  on  the  cathodes,  are  rapidly  re- 
moved, and  layers  of  fluid  richer  in  metal  are  conveyed  to  the 
cathodes,  the  greatest  possible  homogeneity  of  the  bath  being 
thus  effected,  and  the  operation  of  deposition  becoming 
uniform. 

Baths  in  motion  show  less  inclination  to  the  formation  of 
buds  and  other  rough  excrescences,  and  hence  the  current- 
density  may  be  greater  than  with  solutions  at  rest,  the  result 

*Zeitschrift  fur  physikalishe  Chemie,  xxxv,  641. 


GALVANOPLASTY  (REPRODUCTION).  583 

being  that  deposition  is  effected  with  greater  rapidity.  These 
experiences  gathered  in  electro-metallurgical  operations  on  a 
large  scale,  have  been  advantageously  applied  to  galvano- 
plasty. 

Stirring  contrivances. — Constant  agitation  of  the  copper  bath 
may  be  effected  in  various  ways.  A  mechanical  stirring  con- 
trivance may  be  provided,  or  agitation  may  be  effected  by 
blowing  in  air,  or  finally,  by  the  flux  and  reflux  of  the  copper 
solution. 

With  the  use  of  a  stirring  apparatus,  stirring  rods  of  hard 
rubber  or  glass  which  are  secured  to  a  shaft  running  over  the 
bath,  swing  like  pendulums,  between  the  electrodes.  This 
motion  of  the  shaft  is  effected  by  means  of  leverage  driven 
from  a  crank  pulley.  The  stirring  rods  should  not  move 
with  too  great  rapidity,  otherwise  the  slime  from  the  anodes, 
which  settles  in  the  bath,  might  be  stirred  up. 

Agitation  of  the  bath  has  also  been  effected  by  slowly  re- 
volving, by  means  of  a  suitable  mechanism,  cast  copper  anodes 
of  a  square  cross-section,  this  mode  of  motion  having  the 
advantage  of  very  thoroughly  mixing  the  electrolyte  without 
being  too  violent. 

If  the  bath  is  to  be  agitated  by  blowing  in  air,  the  latter  is 
forced  in  by  means  of  a  pump  through  perforated  lead  pipes, 
arranged  horizontally  about  two  inches  from  the  bottom  of 
the  tank. 

It  is  best  to  use  a  small  air  compressor  in  connection  with 
an  air  chamber  provided  with  a  safety  valve.  The  quantity 
of  air  to  be  conveyed  to  the  perforated  lead  pipes  is  regulated 
by  means  of  a  cock  or  valve.  The  number  and  size  of  the  per- 
forations in  the  lead  coil  must  be  such  that  the  air  passes  out 
as  uniformly  as  possible  the  entire  length  of  the  pipe,  so  that 
all  portions  of  the  electrolyte  are  uniformly  agitated.  For 
smaller  baths  an  ordinary  well-constructed  air-pump  suffices 
for  pressing  in  the  air. 

Agitation  of  the  bath  by  flux  and  reflux  of  the  solution 
may  be  effected  in  various  ways,  and  is  especially  suitable 
where  many  copper  baths  are  in  operation. 


584 


ELECTRO-DEPOSITION    OF    METALS. 


I 


The  baths  are  arranged  in 
the  form  of  steps.  Near  the 
bottom  each  bath  is  provided 
with  a  leaden  outlet-pipe  ^Fig. 
140),  which  terminates  above 
the  next  bath  over  a  distribut- 
ing gutter,  or  as  a  perforated 
pipe,  h.  From  the  last  bath  the 
copper  solution  flows  from  a 
reservoir,  E,  from  which  it  is 
forced  by  means  of  a  hard- 
rubber  pump,  i,  into  the  reser- 
voir, A,  placed  at  a  higher 
level.  From  A  it  again  passes 
through  the  baths,  B,  C  and  D. 
A  leaden  steam-coil  may,  if 
necessary,  be  placed  in  A,  to 
increase  the  temperature,  if  it 
should  have  become  too  low. 
Over  A  a  wooden  frame  cov- 
ered with  felt  may  be  placed  ; 
the  copper  solution  flowing 
upon  the  frame  and  passing 
through  the  felt,  is  thereby 
filtered. 

While  agitation  of  the  bath 
presents  great  advantages,  there 
is  one  drawback  connected  with 
it,  which,  however,  should  not 
prevent  its  adoption.  With 
baths  at  rest,  dust  and  insolu- 
ble particles  becoming  detached 
from  the  anodes  sink  to  the 
bottom  and  have  no  injurious 
effect  upon  the  deposit.  On 
the  other  hand,  in  agitated 


GALVANOPLASTY  (REPRODUCTION).  585 

baths,  they  remain  suspended  in  the  electrolyte,  and  it  may 
happen  that  they  grow  into  the  deposit,  giving  rise  to  the  for- 
mation of  roughnesses  (buds).  Everywhere  that  such  rough- 
ness is  formed,  it  increases  more  rapidly  in  proportion  to  the 
other  smooth  portions  of  the  cathode,  and  these  excresences 
frequently  attain  considerable  thickness,  which  is  not  at  all 
desirable. 

It  is,  therefore,  advisable  to  make  provision  for  keeping- 
such  baths  perfectly  clean.  Baths  agitated  by  flux  and 
reflux  can  be  readily  filtered,  as  described  above,  previous 
to  their  passing  into  the  collecting  reservoir.  Solutions  agi- 
tated by  a  stirring  contrivance,  or  by  blowing  in  air,  should 
be  occasionally  allowed  to  rest  and  settle.  The  perfectly  clear 
solution  is  then  siphoned  off,  and  the  bottom  layers  are  freed 
from  insoluble  particles  by  filtering.  With  the  use  of  impure 
anodes,  which,  however,  cannot  be  by  any  means  recom- 
mended, it  is  best  to  sew  them  in  some  kind  of  fabric,  for  in- 
stance, muslin,  the  fibers  of  which  have  been  impregnated 
with  ethereal  paraffine  solution  to  make  them  more  resistant 
towards  the  action  of  the  sulphuric  acid.  In  order  to  keep 
the  electrolyte  as  clean  as  possible,  it  is  best  to  treat  chem- 
ically pure  anodes  in  the  same  manner. 

In  case  no  means  for  agitating  the  bath  should  be  available, 
good  results  may,  according  to  Maximowitsch,  be  obtained  by 
the  following  arrangement :  The  electrodes  are  placed  hori- 
zontally and  in  such  a  manner  that  in  the  bath  the  anodes  are 
over  the  cathodes.  The  new  solution  is  thus  formed  in  the 
upper  portions  of  the  bath  on  the  anodes  and  being  specifically 
heavier  than  the  old  exhausted  solution  sinks  to  the  bottom 
where  it  displaces  the  exhausted  solution  poor  in  copper,  the 
latter  being  by  reason  of  its  slighter  specific  gravity  forced  up- 
wards. Hence,  without  the  use  of  any  mechanical  contriv- 
ance the  freshly -formed  solution  is  constantly  mixed  with  the 
old  solution. 

To  prevent  small  particles  of  metal  from  the  anodes  falling 
upon  the  cathodes  and  there  giving  rise  to  the  evolution  of  gas, 


586  ELECTRO-DEPOSITION    OF    METALS. 

a  frame  filled  with  unbleached,  undyed  silk  is  placed  between 
the  two  electrodes. 

For  the  production  of  a  beautiful,  dense  and  firm  deposit, 
according  to  this  process,  Schonbeck  recommends  the  follow- 
ing bath:  GYystallized  blue  vitriol  125  Ibs.,  concentrated  sul- 
phuric acid  12J  Ibs.,  water  500  Ibs. 

Current-density  per  square  decimeter  electrode  surface  6  to  10 
amperes  ;  electro-motive  force  for  every  ampere  0.8  volt ;  electrode 
distance  8  centimeters. 

Anodes. — Annealed  sheets  of  the  purest  electrolytic  copper 
should  be  suspended  in  the  bath.  Impure  anodes  introduce 
other  metallic  constituents  into  the  bath,  and  the  result  might 
be  a  brittle  deposit.  The  use  of  old  copper  boiler  sheets,  so 
frequently  advocated,  is  decidedly  to  be  rejected. 

The  more  impurities  the  anodes  contain,  the  darker  the 
residue  formed  upon  them  will  be,  and  this  residue  in  time 
deposits  as  slime  upon  the  bottoms  of  the  tanks.  Anodes  of 
electrolytically  deposited,  and  therefore  perfectly  pure,  copper 
also  yield  a  residue,  which,  however,  is  of  a  pale  brown  ap- 
pearance, and  consists  of  cuprous  oxide  and  metallic  copper. 
It  is  recommended  daily  to  free  the  anodes  from  adhering 
residues  by  brushing,  so  as  to  decrease  the  collection  of  slime 
in  the  bath.  The  anodes  of  baths  in  motion  are  best  sewed,  as 
above  described,  in  a  close  fabric  to  retain  insoluble  particles. 

In  connection  with  his  previously  mentioned  experiments, 
Forster  ascertained  that  with  the  use  of  ordinary  copper,  at  0.3 
ampere  current-density,  about  7.4  grammes  (4.15  drachms)  of 
red-brown  anode  slime  with  60  to  70  per  cent,  of  copper,  par- 
tially in  the  form  of  cuprous  oxide,  were  at  the  ordinary  tem- 
perature obtained  from  6.6  Ibs.  of  anode  copper.  On  the  other 
hand,  at  a  temperature  of  104°  F.,  only  24  grammes  (1.25 
drachms)  of  a  pale  gray  slime  consisting  chiefly  of  silver,  lead, 
lead  sulphate  and  antimony  combinations  with  only  a  slight 
content  of  copper  were  under  otherwise  equal  conditions  ob- 
tained. By  raising  the  temperature  of  the  electrolyte  to  140° 
F.  the  quantity  of  anode  slime  increased  considerably,  and  at 


GALVANOPLASTY  (REPRODUCTION).  587 

1  ampere  current-density  amounted  to  about  twenty  times  as 
much.  The  slime,  in  addition  to  a  smaller  quantity  of  the 
above-described  pale  gray  slime,  contained  larger  quantities  of 
well-formed  lustrous  copper  crystals  which  could  scarcely  be 
derived  from  the  rolled  copper  anodes.  Wohlwills  made 
analogous  observations  in  the  electrolysis  of  gold  chloride 
solution  containing  hydrochloric  acid,  and  based  upon  these 
observations,  Forster  assumes  that  at  the  higher  temperature 
the  anode  copper  sends  forth  augmented  univalent  cuprous- 
ions  into  the  copper  solution,  the  cuprous  sulphate  solution 
formed  being  decomposed  to  cupric  sulphate  (blue  vitriol) 
while  copper  is  separated,  according  to  the  following  equation  : 

Cu2S04     =      CuS04     +      Cu. 

Cuprous  sulphate.      Cupric  sulphate.       Copper. 

The  anode  surfaces  should  be  at  least  equal  to  that  of  the 
moulds,  and  for  shallow  moulds  the  distance  between  them  and 
the  anodes  may  be  from  2  to  3  inches,  but  for  deeper  moulds 
it  must  be  increased. 

Tanks. — Acid-proof  stoneware  tanks  serve  for  the  reception 
of  the  acid  copper  baths,  or  for  larger  baths,  wooden  tanks 
lined  with  pure  sheet-lead  about  0.11  to  0.19  inch  thick,  the 
seams  of  which  are  soldered  with  pure  lead.  It  should  be 
borne  in  mind  that  a  coat  of  lacquer,  as  previously  men- 
tioned, may  have  an  injurious  effect. 

Rapid  galvanoplasty.  Thus  far  galvanoplastic  baths  with 
an  average  content  of  22  per  cent,  of  blue  vitriol  and  2  to  3 
per  cent,  of  sulphuric  acid  have  only  been  referred  to.  Such 
baths  were  exclusively  used  up  to  the  end  of  1899.  The 
current-density  employed  in  practice  amounted  to  scarcely 
more  than  25  amperes,  and  the  customary  thickness  of  0.15 
to  0.18  millimeters  for  electrotypes  was  at  the  best  attained  in 
4J  to  5  hours. 

The  much-felt  want  of  producing  galvanoplastic  deposits  of 
sufficient  thickness  in  a  materially  shorter  time  gave  rise  to 
search  for  ways  and  means  to  attain  this  object. 


588  ELECTRO-DEPOSITION    OF    METALS. 

Taking  into  consideration  the  fact  that  a  larger  quantity  of 
copper  can  in  a  shorter  time  be  deposited  with  the  use  of 
higher  current-densities,  the  conditions  under  which  the  use 
of  higher  current-densities  becomes  possible  without  leading 
to  the  reduction  of  a  useless,  brittle  or  pulverulent  deposit 
had  to  be  ascertained.  By  the  investigations  of  Hubl  it  had 
been  shown  that  the  production  of  good  deposits  is  by  no 
means  dependent  on  a  high  content  of  sulphuric  acid  in  the 
electrolyte,  but  that  acidulating  the  copper  bath  only  so  far  as 
to  prevent  the  formation  of  basic  salts  suffices. 

It  was  further  known  that  by  the  bath  containing  a  large 
quantity  of  sulphuric  acid,  the  solubility  of  blue  vitriol  is  de- 
creased, and  since  good  deposits  can  with  high  current- 
densities  be  obtained  only  from  highly-concentrated  blue 
vitriol  solutions,  the  reduction  of  the  content  of  sulphuric 
acid  became  an  absolute  necessity. 

There  is,  however,  still  another  reason  why  copper  baths 
working  with  high  current-densities  can  only  be  compounded 
with  small  quantities  of  sulphuric  acid.  It  has  previously 
been  mentioned  that  the  sulphuric  acid  is  dissociated  into 
hydrogen-ions  and  S04-ions,  and  that  hydrogen-ions  effect 
the  reduction  of  copper  in  a  secondary  manner.  By  a  small 
addition  of  sulphuric  acid,  this  secondary  reduction  is  to  be 
largely  avoided,  and  the  copper  is  to  be  brought  to  separate 
chiefly  in  a  primary  manner,  because  by  reason  of  the 
accelerated  process  of  reduction  at  high  current  densities, 
there  is  danger  of  hydrogen-ions  being  brought  to  separate  as 
hydrogen  gas  on  the  cathodes,  which  might  give  rise  to  the 
formation  of  a  sandy  or  spongy  deposit. 

In  a  20  per  cent,  blue  vitriol  solution  compounded  with  1 
per  cent,  of  sulphuric  acid,  the  copper  solution  and  the  sul- 
phuric acid  participate  equally,  according  to  Hubl,  in  con- 
ducting the  current ;  while  with  a  content  of  5  per  cent,  of 
acid,  the  conduction  of  the  current  is  almost  exclusively  taken 
charge  of  by  the  acid-ions.  Thus,  the  smaller  the  content  of 
free  sulphuric  acid,  the  greater  the  quantity  of  primarily  de- 


GALVANOPLASTY  (REPRODUCTION).  589 

posited  copper  will  be,  and  the  less  the  danger  of  hydrogen- 
occlusion,  or  the  formation  of  a  hydrate. 

However,  a  smaller  content  of  sulphuric  acid  in  the  electro- 
lyte, together  with  a  greater  content  of  blue  vitriol,  is  by  itself 
not  sufficient  for  removing  the  possibility  of  the  formation  of 
spongy  deposits  caused  by  the  layers  of  fluid  on  the  cathode 
having  become  poorer  in  metal.  Provision  has  to  be  made 
for  the  vigorous  agitation  of  the  electrolyte,  so  that  the  layers 
poor  in  metal  on  the  cathode  are  constantly  replaced  by  layers 
richer  in  metal,  a  discharge  of  hydrogen-ions  on  the  cathodes 
being  thus  best  prevented  ;  and  coherent  copper-deposits  of 
great  hardness  and  sufficient  tenacity  for  graphic  purposes  are 
even  with  very  high  current-densities  obtained. 

This  process,  based  upon  the  principles  above  mentioned, 
was  perfected  in  1900,  and  the  term  rapid  galvanoplasty  has 
been  applied  to  it. 

It  is  obvious  that  the  term  rapid  galvanoplastic  bath  cannot 
be  claimed  solely  for  one  composition,  but  that  all  acid  copper 
baths  which  yield  deposits  in  a  materially  shorter  time  than 
was  formerly  possible  may  thus  be  designated.  According  to 
the  objects  the  rapidly-working  baths  are  to  serve,  it  would 
even  be  rational  that  their  compositions  should  vary,  as  will 
be  directly  seen. 

While  shallow  impressions,  for  instance,  autotypes,  wood- 
cuts, etc.,  only  require  a  very  small  addition  of  sulphuric  acid, 
for  deep  impressions  of  set-up  type  a  larger  content  of  sulphuric 
acid  is  necessary,  especially  when  the  type  has  been  set  with 
low  spaces.  For  the  reproduction  of  moulds  of  objects  of  art 
in  very  high  relief,  rapid  galvanoplasty  is  only  within  certain 
limits  applicable. 

Below  will  be  given  two  compositions  of  rapid  galvanoplastic 
baths,  which  are  considered  the  highest  and  lowest  limits, 
though  it  is  not  to  be  understood  that  good  results  cannot  be 
obtained  with  baths  containing  more  or  less  blue  vitriol  and 
sulphuric  acid.  These  two  baths,  however,  have  proved  re- 
liable in  practical  rapid  galvanoplasty,  and  the  necessity  for 
other  compositions  will  scarcely  arise. 


590  ELECTRO-DEPOSITION    OF    METALS. 

For  shallow  impressions  of  autotypes,  wood-cuts,  etc. — In  a 
100  quart  bath  :  74.8  Ibs.  of  blue  vitriol,  0.44  Ib.  of  sulphuric 
acid  of  66°  Be. 

Dissolve  the  blue  vitriol  with  the  assistance  of  heat. 

This  bath  being  oversaturated  with  blue  vitriol,  crystals 
would  be  formed,  which  must  by  all  means  be  avoided,  and 
for  this  purpose  the  bath  has  to  be  constantly  kept  at  a  tem- 
perature of  about  78.8°  to  82.4°  F.  At  this  temperature  the 
bath  shows  about  25°  Be.,  and  at  64.4°  F.,  27°  Be. 

Heating  the  bath  is  best  effected  by  means  of  a  lead  coil  on 
the  bottom  of  the  lead-lined  tank,  through  which  steam  is 
introduced  until  the  bath  shows  the  desired  temperature. 
Since,  by  reason  of  the  high  current-densities,  the  temperature 
of  the  bath  is  still  further  increased,  which  might  be  detri- 
mental with  the  use  of  wax  moulds,  the  lead  coil  should  be 
furnished  with  an  additional  branch  for  the  introduction  of 
cold  water  in  case  the  temperature  becomes  excessive. 

It  is  not  likely  that  a  larger  bath  of  the  above-mentioned 
composition  will  cool  off  enough  over  night  for  the  crystalliza- 
tion of  blue  vitriol,  especially  if  it  is  covered  and  the  work- 
room is  not  exceedingly  cold.  There  is  danger  of  the  crystal- 
lization of  blue  vitriol  if  the  work-room  is  not  kept  at  an  even 
temperature,  or  the  bath  is  not  worked  for  one  or  more  days 
in  succession.  In  the  latter  case  it  is  advisable,  the  evening 
before  work  is  stopped,  to  heat  the  bath  more  than  usual  and 
dilute  it  with  water.  The  quantity  of  the  latter  which  has  to 
be  added  to  make  up  what  may  in  a  certain  time  be  lost  by 
evaporation  will  soon  be  learned  by  experience.  If,  for  the 
sake  of  precaution,  the  bath  is  covered,  it  will  be  found  ready 
for  work  when  operations  are  resumed. 

In  order  to  obtain  deposits  of  good  quality  with  high  current- 
densities,  vigorous  agitation  of  the  bath  is  required.  This  is 
most  uniformly  effected  by  blowing  in  air  by  means  of  an  air 
.compressor.  The  bath  may  also  be  agitated,  though  less  uni- 
formly so  in  all  portions,  by  means  of  a  copper  paddle  fitted 
to  the  front  of  the  tank  and  driven  by  means  of  a  band  from 


GALVANOPLASTY  (REPRODUCTION).  591 

a  transmission.  It  is  placed  about  six  inches  above  the  bot- 
tom of  the  tank  and,  the  paddles  being  set  at  an  angle  of  45°, 
a  vigorous  motion  of  the  lower  layers  towards  the  surface  is 
effected. 

If  the  above-mentioned  conditions  be  observed,  the  current- 
density  for  this  bath  may  amount  up  to  6  amperes  per  square 
decimeter,  and  with  a  distance  of  about  6  centimeters  of  the 
cathodes  from  the  anodes,  the  electro-motive  force  will  ap- 
proximately be  (3  volts.  When  working  on  an  average  with 
6  amperes  per  square  decimeter,  a  deposit  of  0.15  millimeter 
thick  will  in  this  bath  be  obtained  in  1J  to  If  hours. 

With  the  use  of  gutta-percha  matrices,  the  bath  may  be 
somewhat  more  heated  than  when  working  with  wax  moulds, 
and  still  higher  current-densities  than  those  given  above  may 
be  employed,  the  deposit  being  then  finished  in  a  still  shorter 
time.  It  is,  however,  advisable  not  to  carry  the  work  of  the 
current  to  an  excess,  otherwise  the  copper  might  readily  show 
properties  not  at  all  desirable. 

It  may,  under  certain  circumstances  be  advantageous,  nay 
even  necessary,  to  face  the  black-leaded  matrices  with  copper 
at  a  somewhat  slighter  current-density,  while  the  bath  is  at 
rest,  i.  e.j  not  agitated  by  a  stirring  contrivance,  or  by  blow- 
ing in  air,  and  to  resume  agitation  and  increase  the  current- 
strength  only  after  the  matrices  are  coated  with  copper. 
Thus,  according  to  the  size  of  the  galvanoplastic  plant,  it  may 
be  desirable  to  have  a  smaller  coppering  bath  not  furnished 
with  a  stirring  contrivance,  from  which  the  matrices,  after 
having  been  faced  with  copper,  are  transferred  to  the  agitated 
bath. 

It  may  here  be  remarked  that  Knight's  process  of  coppering 
the  matrices  with  neutral  blue  vitriol  solution  and  iron  fil- 
ings, which  is  much  liked,  is  not  applicable  in  rapid  galvano- 
plasty.  In  suspending  such  matrices  coated  with  copper  in 
the  rapid  bath,  the  slight  copper-film  is,  so  to  say,  burnt,  and 
a  proper  deposit  can  no  longer  be  effected. 

In  a  bath  of  the  composition  given  above,  it  is  sometimes 


592  ELECTRO-DEPOSITION    OP    METALS. 

difficult  to  obtain  with  the  above-mentioned  high  current- 
densities  unexceptionable  electrotypes  from  matrices  produced 
from  deep  and  steep  set-up  type.  The  shallow  portions,  to  be 
sure,  copper  well,  but  the  copper  does  not  spread  into  the 
deeper  portions,  and  holes  are  left.  By  the  addition  of  certain 
substances,  for  instance,  alcohol,  this  drawback  can,  to  be  sure, 
be  somewhat  improved,  but  not  entirely  removed,  and  for  this 
reason  such  matrices  are  further  worked  in  a  bath,  the  compo- 
sition of  which  is  given  below.  It  is,  however,  preferable  to 
preparatively  copper  such  type-compositions,  especially  when 
low  spaces  have  been  used,  and  after  about  J  hour  to  transfer 
the  matrices  to  the  rapid  galvanoplastic  bath.  By  working  in 
this  manner,  the  electrotypes  will  be  free  from  holes,  and  fin- 
ishing even  the  largest  customary  forms  will  not  require  more 
than  2  hours. 

For  deep  impressions. — In  a  100-quart  bath  :  57.2  Ibs.  of  blue 
vitriol,  1.76  Ib.  of  sulphuric  acid. 

It  is  recommended  not  to  deposit  at  a  lower  temperature  of 
the  bath  than  68°  F.,  though  with  this  concentration  the 
danger  of  crystallization  is  less.  For  heating  and  cooling  the 
electrolyte,  a  lead  coil,  as  previously  described,  is  advantage- 
ously used,  and  provision  for  thorough  agitation  has  to  be 
made.  This  bath  is  generally  allowed  to  work  with  4.5  to  5 
amperes  current-density,  the  electro-motive  force,  with  a  dis- 
tance of  6  centimeters  of  the  anodes  from  the  cathodes,  amount- 
ing then  to  about  4|  volts.  The  copper  deposit  attains  in  2J 
hours  a  thickness  of  0.15  millimeter,  and  in  2f  hours  one  of 
0.18  millimeter.  Higher  current-densities  are  also  permis- 
sible, and  the  operator  will  soon  find  out  how  far  he  can  go  in 
this  respect. 

Deeper  forms  become  well  covered,  especially  if,  according 
to  Rudholzner's  proposition,  about  1  Ib.  of  alcohol  is  added. 
But,  nevertheless,  it  is  recommended  to  preparatively  copper 
in  the  ordinary  acid  copper  bath  impressions  of  very  steep 
set-up  type  with  low  spaces,  as  with  the  use  of  high  current- 
densities  the  streaks  which  are  temporarily  formed  upon 


GALVANOPLASTY    (REPRODUCTION).  593 

the  printing  faces  of  the  electrotypes  are  thus  most  surely 
avoided. 

Heating  the  baths  may  be  omitted  in  plants  lacking  the 
necessary  contrivances.  The  blue  vitriol  solution  must  then 
be  of  such  a  composition  as  to  preclude  all  danger  of  blue 
vitriol  crystallizing  out  even  at  the  lowest  temperature  of  the 
work-room.  Somewhat  lower  current-densities  corresponding 
to  the  slighter  concentration  have  of  course  to  be  used. 

Regarding  the  quality  of  the  copper  deposit  effected  with 
high  current-densities,  it  may  be  said  that  its  tenacity  is  good, 
better  in  the  second  bath  than  in  the  one  first  mentioned,  but 
in  all  cases  sufficient  for  the  electrotypes.  The  copper  is  how- 
ever, decidedly  somewhat  harder  than  that  deposited  from  the 
ordinary  baths  as  proved  by  its  slight  wear  in  printing. 

The  treatment  of  the  rapid  galvanoplastic  baths  will  be 
readily  understood  from  what  has  been  said  above.  On  the 
one  hand,  the  baths  must  riot  be  allowed  to  cool  to  a  tempera- 
ture at  which  the  blue  vitriol  would  no  longer  be  held  in 
solution,  but  would  crystallize  ;  and,  on  the  other,  the  reaction 
has  from  time  to  time  to  be  tested  with  red  congo  paper  which 
must  acquire  a  plainly-perceptible  blue  color.  If  such  is  not 
the  case,  no,  or  too  little,  free  sulphuric  acid  is  present  in  the 
bath,  and  brittle  deposits  will  be  formed  which  cannot  be  de- 
tached whole  from  the  matrices.  When  this  is  noticed  add 
0.44  Ib.  of  sulphuric  acid  per  100  quarts  of  bath,  or  1.76  Ib. 
to  the  bath  for  deep  impressions. 

The  excess  of  acid  is  very  rapidly  consumed  with  the  use  of 
copper  plates  which  have  been  electrically  deposited  and, 
without  recasting  and  rolling,  suspended  as  anodes  in  the 
bath.  The  use  of  rolled  anodes  is  therefore  absolutely  neces- 
sary, and,  as  previously  described,  they  should  be  sewed  in  a 
close  fabric  to  avoid  contamination  of  the  bath  by  the  anode- 
slime  formed,  and  by  small  copper  crystals. 

Special  attention  should  be  paid  to  furnish  the  matrices  with 
conductors  of  sufficiently  large  cross-section  corresponding  to 
the  great  current-strengths.  This  will  later  on  be  referred  to. 
38 


594  ELECTRO-DEPOSITION    OF    METALS. 

Examination  of  the  Acid  Copper  Baths'. 

The  copper  withdrawn  from  the  bath  by  deposition  is  only 
partially  restored,  but  not  entirely  replaced,  by  the  anodes, 
and  hence  the  content  of  copper  will  in  time  decrease,  and  the 
content  of  free  acid  increase.  The  deficiency  of  copper  can, 
however,  be  readily  replaced  by  suspending  bags  filled  with 
blue  vitriol  in  the  bath,  while  too  large  an  excess  of  acid  is 
removed  by  the  addition  of  copper  carbonate  or  cuprous  oxide 
(cupron). 

However,  in  order  not  to  grope  in  the  dark  in  making  such 
corrections  of  the  bath,  it  is  necessary  to  determine  from  time 
to  time  the  composition  of  the  copper  solution  as  regards  the 
content  of  copper  and  acid,  for  which  purpose  the  methods 
described  below  may  be  used. 

Determination  of  Free  Acid. — The  free  acid  is  determined  by 
titrating  the  copper  solution  with  standard  soda  solution, 
congo-paper  being  used  as  an  indicator.  Bring  by  means  of  a 
pipette,  10  cubic  centimeters  of  the  copper  bath  into  a  beaker, 
dilute  with  the  same  quantity  of  distilled  water,  and  add  drop 
by  drop  from  a  burette  standard  soda  solution,  stirring  con- 
stantly, until  congo-paper  is  no  longer  colored  blue  when 
moistened  with  a  drop  of  the  solution  in  the  beaker.  Since  1 
cubic  centimeter  of  standard  soda  solution  is  equal  to  0.049 
gramme  of  free  sulphuric  acid,  the  cubic  centimeters  of  stand- 
ard soda  solution  used  multiplied  by  4.9  give  the  number  of 
grammes  of  free  sulphuric  acid  per  liter  of  bath. 

Volumetric  determination  of  the  content  of  copper  according  to 
Haerts  method. — This  method  is  based  upon  the  conversion  of 
blue  vitriol  and  potassium  iodide  into  copper  iodide  and  free 
iodine.  By  determining  the  quantity  of  separated  free  iodine 
by  titrating  with  solution  of  sodium  hyposulphite  of  known 
content,  the  content  of  blue  vitriol  is  found  by  simple  calcu- 
lation. The  process  is  as  follows  :  Bring  10  cubic  centimeters 
of  the  copper  bath  into  a  measuring  flask  holding  -^  liter, 
neutralize  the  free  acid  by  the  addition  of  dilute  soda  lye  until 
a  precipitate  of  bluish  cupric  hydrate,  which  does  not  disap- 


GALVANOPLASTY    (REPRODUCTION).  595 

pear  even  with  vigorous  shaking,  commences  to  separate. 
Now  add,  drop  by  drop,  dilute  sulphuric  acid  until  the  pre- 
cipitate just  dissolves ;  then  fill  the  measuring  flask  up  to  the 
mark  with  distilled  water,  and  mix  by  vigorous  shaking.  Of 
this  solution  bring  10  cubic  centimeters  by  means  of  a  pipette 
into  a  flask  of  100  cubic  centimeters'  capacity  and  provided 
with  a  glass  stopper;  add  10  cubic  centimeters  of  a  10  per 
cent,  potassium  iodide  solution  ;  dilute  with  some  water,  and 
allow  the  closed  vessel  to  stand  about  10  minutes.  Now  add 
from  a  burette,  with  constant  stirring,  a  decinormal  solution 
of  sodium  hyposulphite  until  starch-paper  is  no  longer  colored 
blue  by  a  drop  of  the  solution  in  the  flask.  Since  1  cubic 
centimeter  of  decinormal  solution  corresponds  to  0.0249 
gramme  of  blue  vitriol  (=  0.0003  gramme  of  copper),  the 
content  of  blue  vitriol  in  one  liter  of  the  solution  is  found  by 
multiplying  the  number  of  cubic  centimeters  of  decinormal 
solution  used  by  24.9.  For  the  correctness  of  the  result  it  is 
necessary  that  the  copper  bath  should  be  free  from  iron. 

The  electrolytic  determination  oj  the  copper  being  more  simple, 
it  is  to  be  preferred  to  the  volumetric  method.  Bring  by 
means  of  the  pipette  10  cubic  centimeters  of  the  copper  bath 
into  the  previously  weighed  platinum  dish,  add  2  cubic  centi- 
meters of  strong  nitric  acid,  fill  the  dish  up  to  within  1  centi- 
meter of  the  rim  with  distilled  water,  and  electrolyze  with  a 
current-strength  ND  100  =  1  ampere. 

Deposition  of  copper  is  finished  when  a  narrow  strip  of 
platinum  sheet  placed  over  the  rim  of  the  dish  and  dipping 
into  the  fluid  shows  in  10  minutes  no  trace  of  a  copper  de- 
posit, which  is  generally  the  case  in  3J  hours.  The  deposit 
is  then  washed  without  interrupting  the  current,  rinsed  with 
alcohol  and  ether,  and  dried  for  a  short  time  at  212°  F.  in 
the  air-bath.  The  increase  in  weight  of  the  platinum  dish 
multiplied  by  100  gives  the  content  of  metallic  copper  in 
grammes  per  1  liter  of  bath.  To  find  the  content  of  blue 
vitriol,  multiply  the  found  content  of  copper  per  liter  by  3.92, 
or  multiply  the  content  of  copper  determined  in  10  cubic 
centimeters  of  bath  by  3.92. 


596  ELECTRO-DEPOSITION    OF    METALS. 

If  now  the  content  of  free  acid  and  of  the  blue  vitriol  in  the 
bath  has  been  ascertained,  a  comparison  with  the  contents 
originally  present  in  preparing  the  bath  will  show  how  many 
grammes  per  liter  the  content  of  acid  has  increased,  and  how 
many  grammes  the  content  of  copper  has  decreased.  Then 
by  a  simple  calculation  it  is  found  how  much  dry  pure  copper 
carbonate  has  to  be  added  per  liter  of  solution  to  restore  the 
original  composition.  For  each  gramme  more  of  sulphuric 
acid  than  originally  present,  1.26  grammes  of  copper  carbon- 
ate have  to  be  added,  and  each  gramme  of  copper  carbonate 
increases  the  content  of  blue  vitriol  2.02  grammes  per  liter  of 
bath.  By  reference  to  these  data  the  operator  is  enabled  to 
calculate  whether  the  quantity  of  copper  carbonate  added  for 
the  neutralization  of  the  excess  of  free  acid  suffices  to  restore 
the  original  content  of  blue  vitriol,  or  whether,  and  how 
much,  blue  vitriol  per  liter  has  to  be  added. 

With  the  use  of  baths  in  which  the  solutions  circulate,  the 
additions  are  best  made  in  the  reservoir  placed  at  a  higher 
level,  into  which  the  solution  constituting  the  bath  is  raised 
by  means  of  a  pump.  The  composition  of  such  baths,  con- 
nected one  with  the  other,  is  the  same,  and  a  single  determi- 
nation of  the  content  of  copper  and  free  sulphuric  acid  will 
suffice.  However,  with  baths,  the  contents  of  which  do  not 
circulate  and  are  not  mixed,  a  special  determination  has  to  be 
made  for  each  bath,  and  the  calculated  additions  have  to  be 
made  to  each  separate  bath. 

Operations  in  Galvanoplasty  for  Graphic  Purposes. 

The  manipulations  for  the  production  of  galvanoplastic 
deposits  for  printing  books  and  illustrations  will  first  be 
described. 

1.  Preparation  of  the  moulds  (matrices)  in  plastic  material 
If  a  negative  of  the  original  for  the  production  of  copies  is 
not  to  be  made  by  direct  deposition  upon  a  metallic  object, 
it  has  to  be  prepared  by  moulding  the  original  either  in  a 
plastic  mass  which,  on  hardening,  will  retain  the  forms  and 


GALVANOPLASTY    (REPRODUCTION).  597 

lines  of  the  design  to  the  finest  hatchings,  or  in  a  material, 
which  plastic  itself,  retains  the  impression  unaltered.  Suitable 
materials  for  this  purpose  are :  Gutta-percha,  wax  (stearine, 
etc.),  and  lead. 

The  preparation  of  moulds  in  gutta-percha  and  wax  will  first 
be  described,  and  the  production  of  metallic  matrices  will  be 
referred  to  in  the  next  section. 

a.  Moulding  in  gutta-percha. — For  the  reproduction  of  the 
fine  lines  of  a  wood-cut  or  copper-plate,  pure  gutta-percha, 
freed  by  various  cleansing  processes  from  the  woody  fibers, 
earthy  substances,  etc.,  found  in  the  crude  product,  is  very 
suitable.  Besides  the  requisite  degree  of  purity,  the  gutta- 
percha  should  possess  three  other  properties,  viz.,  it  must 
become  highly  plastic  by  heating,  without,  however,  becoming 
sticky,  and  finally  it  should  rapidly  harden. 

The  most  simple  way  of  softening  gutta-percha  is  to  immerse 
it  in  water  of  170°  to  190°  F.  When  thoroughly  softened  no 
hard  lumps  should  be  felt  on  kneading  with  the  hands,  which 
should  be  kept  thoroughly  moistened  with  water  during  the 
operation.  A  fragment  of  the  gutta-percha  corresponding  to 
the  size  of  the  object  to  be  moulded  is  then  rolled  into  a  plate 
about  J  to  }  inch  thick.  To  facilitate  the  detachment  of  the 
mould  after  cooling,  the  surface  of  the  gutta-percha  which  is 
to  receive  the  impression  should  be  well  brushed  with  black- 
lead  (plumbago  or  graphite),  an  excess  of  it  being  removed  by 
blowing. 

The  original  (wood-cut,  autotype,  set-up  type,  etc.)  must  be 
firmly  locked  in  the  usual  manner,  and  the  surface  is  then 
cleansed  from  dirt  and  stale  ink  by  brushing  with  benzine. 
When  dry  it  is  brushed  over  with  plumbago,  an  excess  of  it 
being  removed  by  means  of  a  bellows. 

The  black-leaded  surface  of  the  warm  gutta-percha  plate  is 
then  placed  upon  the  black-leaded  face  of  the  original,  and 
after  gently  pressing  the  former  with  the  hand  upon  the  latter, 
the  whole  is  placed  in  the  press. 

b.  Moulding  in  wax. — Beeswax  is  a  very  useful  material  for 


598  ELECTRO-DEPOSITION    OF    METALS. 

preparing  moulds,  but,  like  stearine,  it  is  according  to  the 
temperature  now  softer  and  now  harder,  which  must  be  taken 
into  consideration.  In  the  cold  state  pure  beeswax  is  quite 
brittle,  and  apt  to  become  full  of  fissures  in  pressing.  To 
decrease  the  brittleness  certain  additions  are  made  to  the  wax; 
various  formulas  for  such  compositions  recommended  by  dif- 
ferent authors  are  here  given  : 

a.  White   wax    120   parts,   stearin   50,   tallow    30,   Syrian 
asphalt  40,  elutriated  graphite  5.     (G.  L.  von  Kress). 

b.  Yellow  beeswax   700  parts,  paraffin  100,  Venetian  tur- 
pentine 55,  graphite  175 ;  or,  cake  wax  50  parts,  yellow  wax 
50,  ceresin  15,  Venetian  turpentine  5.     (Karl  Kempe). 

c.  Wax  20  parts,  thick  turpentine  20,  rosin  10,  graphite  50. 
(Hackewitz).     By  reason  of  its  large  content  of  graphite,  this 
composition    which    is   excellent    in    every    respect,    can    be 
recommended  for  taking  moulds  from  objects  which  can  be 
black-leaded  only  with  difficulty. 

d.  Yellow  wax  900  parts,  Venetian  turpentine  135,  graphite 
22.     (Urquhart). 

e.  Pure  beeswax  850  parts,  crude  turpentine    100,  elutri- 
ated  graphite  50.     (Furlong).     The  mixture  is  to  be  freed 
from  all  moisture  by  boiling  in  a  steam  pot  for  2  hours.     In 
the  hot  season  of  the  year  it  is  recommended  to  add  50  parts 
of  burgundy  pitch  to  impart  greater  hardness  to  the  wax. 

/.  Pfanhauser  recommends  the  following  composition  es- 
pecially for  taking  moulds  from  undercut  objects.  The  mass 
is  very  elastic  and  objects  with  quite  wide  projecting  portions 
can,  with  care,  be  moulded  with  it. 

Yellow  beeswax  400  parts,  ozocerite  300,  paraffine  100, 
Venetian  turpentine  60,  elutriated  graphite  100.  For  use  in 
the  summer  months  the  composition  of  the  mass  is  as  follows  : 
Yellow  beeswax  250  parts,  ozocerite  450,  paraffin  50,  Ve- 
netian turpentine  35,  elutriated  graphite  180. 

The  proportions  given  in  the  formulas  cannot  always  be 
strictly  adhered  to  and  one  has  to  be  guided  by  prevailing 
conditions.  If  the  wax  turns  out  rather  brittle,  somewhat 


GALVANOPLASTY  (REPRODUCTION).  599 

more  tallow  or  turpentine  has  to  be  added  and,  on  the  other 
hand,  in  the  hot  season  of  the  year  when  the  wax  is  too  soft, 
a  smaller  quantity  of  turpentine  or  tallow  will  have  to  be 
used. 

To  avoid  overheating  it  is  advisable  not  to  melt  the  wax 
mixture  over  an  open  fire,  and  a  jacketed  kettle  heated  by 
steam  or  gas  is  generally  used.  With  the  use  of  steam,  the 
latter  passes  through  a  valve  into  the  jacket  while  the  con- 
densed water  is  discharged  through  another  valve.  When 
gas  is  used  the  space  between  the  jacket  and  kettle  is  filled 
with  water,  the  latter  being  from  time  to  time  replenished  as 
evaporation  progresses. 

Two  wax-melting  kettles  will  be  required,  because  the  wax 
which  has  been  in  contact  with  the  bath,  has  to  be  entirely  freed 
from  water  in  the  one  kettle  before  it  can  be  again  used  for 
moulding.  The  dehydrated  wax  is  then  transferred  to  the 
other  kettle. 

To  prepare  the  wax  for  receiving  the  impression,  pour  the 
melted  composition  in  the  mould-box,  which  is' a  tray  of  suffi- 
cient size  with  shallow  sides  about  J  inch  in  depth  all  round, 
and  with  a  continuation  of  the  bottom  plate  on  one  of  the 
shorter  sides  for  about  3  inches  beyond  the  box,  to  allow  of  its 
being  supported  by  hooks  from  the  conducting  rods  of  the 
bath.  The  moulding-box  is  placed  upon  a  level  surface  and 
filled  to  the  brim.  Air  bubbles  and  other  impurities  forming 
on  the  surface  are  at  once  removed  by  a  touch  with  a  hot  iron 
rod. 

The  surface  of  the  wax,  while  still  luke-warm,  is  then  dusted 
over  with  the  finest  plumbago.  The  black-leaded  original  is 
then  placed,  face  downwards,  upon  the  wax  surface  and  sub- 
mitted to  intense  pressure.  When  black-leading  has  been 
carefully  done,  the  original  can  be  readily  and  perfectly  de- 
tached from  the  mould.  Some  operators  apply  a  light  coat  of 
oil  to  the  original  in  place  of  black -leading  it,  but  care  must 
be  taken  not  to  leave  any  considerable  portion  of  oil  upon  the 
original. 


600  ELECTRO-DEPOSITION    OF    METALS. 

In  this  country,  before  the  impression  is  taken,  the  wax  plate 
or  wax  mould  is  frequently  treated  as  follow  :  Black-lead  and 
water  are  mixed  to  the  consistency  of  cream.  The  mixture  is 
carefully  and  uniformly  applied  to  the  wax  plate  and  rubbed 
dry  with  the  hand. 

The  method  above  described,  according  to  which  the  melted 
wax  is  poured  in  the  moulding-box  is  constantly  more  and 
more  abandoned,  the  work  being  generally  done  as  follows : 

Lead  plates,  the  size  of  the  original  to  be  moulded,  are  cast, 
laid  upon  the  wax-moulding  table,  and  enclosed  by  a  rim  of 
the  depth  of  the  required  thickness  of  the  wax  plate.  The 
box  thus  formed  is  then  filled  to  the  brim  with  melted  wax, 
air-bubbles  and  other  impurities  being  removed,  any  excess 
of  wax  cut  off,  and  the  mould  black-leaded  by  means  of  a  soft 
brush.  In  some  galvanoplastic  plants  the  moulded  wax  plates, 
previous  to  making  the  impressions,  are  planed  perfectly  level 
by  a  shaving  machine.  While  gutta-percha  matrices  will 
bear  quite  vigorous  treatment  with  the  brush,  care  must  in 
this  respect  be  exercised  with  wax  matrices  to  prevent  in- 
jury. 

The  wax  plates  prepared  according  to  the  process  just 
described  are  black-leaded  and  laid  upon  the  originals  to  be 
moulded,  the  whole  being  then  placed  under  the  press. 

2.  Presses. — For  making  the  impressions  of  the  form  in  the 
moulding  composition,  a  moulding  press  is  used  which  is  cap- 
able of  giving  a  gradual  and  powerful  pressure.  Fig.  141 
represents  a  form  of  moulding  press  in  common  use,  and 
known  as  the  "  toggle  "  press.  It  consists  of  a  massive  frame 
having  a  planed,  movable  bed,  over  which  a  head  is  moved 
on  pivots  and  counter-balanced  by  a  heavy  weight,  as  shown, 
so  that  it  can  be  readily  thrown  up,  having  the  bed  exposed, 
the  black-leaded  type  form  being  placed  on  the  bed.  The 
well  black-leaded  case  is  attached  by  clamps  to  the  movable 
head,  or  the  form  (also  black-leaded)  is  laid  face  down  on  the 
case,  and  the  head  is  then  turned  down  and  held  in  place  by 
the  swinging  bar  (shown  turned  back  in  the  cut).  All  being 


GALVANOPLASTY  (REPRODUCTION). 


601 


ready,  the  toggle-pressure  is  put  on  by  means  of  the  hand- 
wheel  and  screw,  the  result  being  to  raise  the  bed  of  the  press 
with  an  enormous  pressure,  causing  the  face  of  the  type  form 
to  impress  itself  into  the  exposed  moulding  surface. 


Fig.  142  represents  a  form  of  "  hydraulic  press  "  less  com- 
monly used  than  that  just  described.  It  is  provided  with 
projecting  rails  and  sliding  plate,  on  which  the  form  and  case 
are  arranged  before  being  placed  in  the  press.  The  pump, 
which  is  worked  by  hand,  is  supported  by  a  frame-work  on 


602 


ELECTRO-DEPOSITION    OF    METALS. 


the  cistern  below  the  cylinder,  and  is  furnished  with  a  gradu- 
ated adjustable  safety-valve  to  give  any  desired  pressure. 

Metal  matrices. — Attempts  have  for  many  years  been  made 
to  mould  originals  in  lead,  since  lead  matrices  possess  many 
advantages  over  gutta-percha  and  wax  matrices  as  they  do 
not  require  to  be  rendered  conductive  by  black-leading,  and 
no  changes  in  dimensions  take  place  in  consequence  of  the 
transition  from  the  heated  into  the  cold  state.  However, 

FIG.  142. 


objects  readily  liable  to  injury,  such  as  wood  cuts,  composi- 
tions, etc.,  could  not  withstand  the  pressure  required  for  im- 
pression in  lead  plates,  and  were  demolished  ;  steel  plates  at 
the  utmost  were  capable  of  standing  the  high  pressure. 
Serviceable  results  were  not  obtained,  even  with  the  use  of 
very  thin  lead  foil  backed,  in  pressing,  with  moist  paste-board 
or  gutta-percha,  because  the  portions  of  the  lead  foil  subject  to 
the  most  severe  demands  would  tear. 


GALVANOPLASTY  (REPRODUCTION).  603 

To  Dr.  E.  Albert  of  Munich  is  due  the  credit  of  having  dis- 
covered the  cause  to  which  these  failures  were  due,  and  of 
having  devised  a  method  for  the  rational  preparation  of  metal 
matrices. 

Dr.  Albert  says  in  reference  to  this  matter  *  :  ."  Every  gal- 
vanoplastic  operator  knows  that  in  making  impressions  of 
forms  of  mixed  composition  and  illustration,  that  the  compo- 
sition down  to  the  quads  is  impressed  before  the  shades,  for 
instance,  of  a  wood  cut  or  an  autotype,  are  finished.  In  mak- 
ing impressions,  the  moist  paste-board  referred  to  above  acted 
exactly  in  the  same  manner  as  wax  or  gutta-percha  softened 
by  heating ;  i.  e.  by  the  moist  paste-board  the  lead  foil  had  to 
be  pressed  first  into  the  deeper,  and  finally  into  the  more 
shallow  depressions.  Notwithstanding  the  enormous  ductility 
of  lead,  the  lead  foil  could  not  satisfy  these  demands  on  ex- 
tension and,  in  consequence  of  this  over-demand,  tore  in  many 
places.  Hence  this  process  was  not  available  for  general 
practice,  it  being  at  the  utmost  suitable  only  for  forms  with 
very  slight  differences  in  level,  and  even  not  for  this  purpose 
with  the  large  forms  now  in  general  use. 

It  must  be  borne  in  mind  that,  for  instance,  upon  a  square 
millimeter  of  an  autotype  there  are  36  depressions  into  which 
the  lead  foil  has  to  be  pressed  and  to  144  side-walls  per  square 
millimeter  of  which  it  has  to  attach  itself.  Especially  with 
under-etched  printing  forms  considerable  force  is  required  to 
detach  the  matrix  from  the  moulding  material,  and  it  is  there- 
fore impossible  with  larger  forms  to  manipulate  the  lead  foil 
which,  for  the  sake  of  decreasing  the  pressure,  has  to  be  very 
thin  so  as  to  maintain  at  the  same  time  a  level  surface. 

This  method  of  impression  by  which  the  parts  correspond- 
ing to  the  dark  portions  of  the  original  can  only  be  impressed 
when  the  moulding  material  has  been  forced  into  the  last  cor- 
ner of  the  deepest  depressions  of  a  printing  form,  is  not  pre- 
meditated nor  one  by  choice,  but  is  conditioned  on  the  physical 

*Zur  Theorie  und  Praxis  der  Metall-matrize,  1905. 


604  ELECTRO-DEPOSITION    OP    METALS. 

properties  of  the  material  itself.  The  pressure  required  to  force 
the  moulding  material  into  the  smallest  depressions  cannot 
be  applied  so  long  as  the  moulding  material  has  a  chance  to 
escape  into  an  empty  space. 

In  consequence  of  this  property  the  matrices  have  to  under- 
go extensive  manipulations,  since  the  large  angular  elevations 
which  correspond  to  the  depressions  of  the  printing  form  would 
prevent  the  further  development  of  the  electro,  especially  also 
the  formation  of  the  copper-deposit  upon  the  matrix.  Hence 
the  prominent  portions  have  to  be  removed  in  the  known 
manner. 

This  necessary  after-manipulation  would  of  course  be  im- 
practicable with  matrices  of  thin  lead  foils,  and  for  this  reason 
also  the  method  is  not  available  for  line-etching,  wood-cut  and 
composition. 

In  the  preceding  it  has  been  specified  as  characteristic  of  the 
bodies  hitherto  used  for  the  preparation  of  matrices  that  the 
Impression  of  the  deepest  depressions  takes  place  before  that  of 
the  more  shallow  ones;  with  soft  metals,  particularly  with  lead, 
just  the  reverse  is  the  case.  The  interior  coherence  of  the 
body-molecules  is  so  much  greater  in  comparison  with  wax 
and  gutta-percha  mass,  or  moistened  paste-board,  that  at  the 
commencement  of  the  pressure  the  lateral  escape  is  avoided, 
whereby  the  moulding  material  yields  first  in  the  direction  of 
the  pressure  and  fills  the  smallest  depressions.  Only  with  in- 
creasing pressure,  which  is  necessary  for  forcing  the  lead  into 
the  deeper  depressions  of  the  printing  form,  the  lead  also 
begins  to  yield  laterally  in  the  region  of  the  portions  pressed 
first. 

Independent  of  the  fact  that  the  small  points  already  im- 
pressed, which  correspond  to  the  smallest  impressions  of  the 
printing  form,  are  again  impressed,  this  pushing  of  the  lead 
has  the  further  drawback  that  the  lead  firmly  settles  in  these 
smallest  depressions,  thus  rendering  the  original  useless. 

Besides,  there  is  no  type  composition,  no  wood-cut,  etc.,  the 
printing  elements  of  which,  especially  when  standing  isolated, 


GALVANOPLASTY  (REPRODUCTION).  605 

could  withstand  the  enormous  pressure  which  has  to  be  used 
for  forcing  a  lead  plate  at  least  5  millimeters  thick  into  the 
large  depressions.  However,  such  a  thickness  of  the  lead 
plate  would  be  necessary  just  as  with  wax  and  gutta-percha 
impressions,  since  the  difference  in  height  between  printing 
and  justifying  surface  is  about  1  cicero  =  4.5  millimeters. 

Hence,  with  the  means  hitherto  available,  the  production  of 
matrices,  either  with  thin  or  thick  metal  plates,  was  imprac- 
ticable, and  until  lately  recourse  had  to  be  had  to- the  old  and 
qualitatively  inferior  wax  and  gutta-percha  matrices,  till  Dr. 
Albert,  in  1903,  succeeded  in  finding  a  method  for  the  rational 
production  of  metal  matrices. 

This  method  is  based  upon  a  number  of  inventions  patented 
in  all  civilized  countries,  and  the  characteristic  features  of  the 
process  will  here  be  briefly  given. 

The  basis  for  the  solution  of  the  problem  rested  upon  the 
adoption  of  such  a  thickness  of  the  metal  plate,  that  the  man- 
ipulations required  for  the  production  of  the  matrix  and  its 
after-manipulations  without  deformation  could  be  effected  by 
the  hand  of  any  workman  ;  as  well  as  upon  a  new  method  of 
impressing  which  would  render  it  possible  for  the  thickness  of 
the  plate  to  be  materially  less  than  the  relief  difference  of  the 
printing  form. 

While  in  the  production  of  medals  and  coins  by  means  of 
galvanoplasty,  the  problem  consists  in  a  perfectly  detached 
reproduction  of  all  the  differences  in  level  of  the  original,  with 
an  electro  for  graphic  purposes,  the  impression  of  the  matrix 
in  the  large  depressions  is  only  a  matter  of  technical  necessity 
so  that  in  the  subsequent  use  of  the  electro  for  printing  the 
white  portion  will  not  smear.  This  knowledge  led  to  the  ex- 
pedient of  pressing  or  bending  by  means  of  a  support  of  a  soft 
body,  the  about  2  millimeters  thick  lead  plates  only  so  far 
into  the  above-mentioned  depressions  as  required  for  technical 
reasons. 

Hence  this  method  of  impression  is  based  upon  a  combina- 
tion of  pressing  and  bending.  The  lead  is  bent  to  a  greater 


606 


ELECTRO-DEPOSITION    OF    METALS. 


extent  the  larger  and  wider  the  sunk  surface  is,  the  electro 
automatically  receiving  thereby  all  the  white  portions  of  such 
depth  that  they  do  not  smear  in  printing. 

The  process  may  be  explained  by  Figs.  143  and  144. 

Fig.  143  represents  the  arrangement  of  the  platen,  lead 
plate,  and  soft  intermediate  layer  previous  to  the  moment  of 
impression.  The  material  used  for  the  intermediate  layer 
must  possess  certain  properties  and  must  be  softer  than  the 
moulding  material.  It  should  be  compressible  without  materi- 
ally yielding  laterally  under  pressure  and,  by  reason  of  elas- 
ticity or  internal  friction,  also  oppose  a  certain  resistance  to 
compression  in  order  to  bend  with  this  resisting  power  of  the 
lead-plate  where  the  latter  lies  hollow.  On  the  other  hand,  it 

FIG.  143. 


must  not  be  too  soft  in  the  sense  of  its  affinity  to  a  liquid 
aggregate  state,  as,  for  instance,  heated  wax,  but  it  should  be 
more  porously  soft  either  in  conformity  with  its  nature  or  its 
arrangement.  In  principle  the  latter  is  generally  based  upon 
the  production  of  many  empty  intermediate  spaces  in  the 
material  (wood  shavings  and  snow  are  softer  than  wood  and 
ice),  or  upon  placing  many  thin  layers  of  the  material  one 
above  the  other.  Such  bodies  can  be  compressed  without- 
yielding  too  much  laterally.  If  the  character  of  the  body 
approaches  more  the  liquid  state,  more  elastic  properties  have 
to  be  added,  which  by  their  tendency  to  equalize  the  change 
suffered  in  form  counteract  the  lateral  yielding,  or  other 
checks  have  to  be  arranged.  Besides,  a  certain  degree  of 


GALVANOPLASTY    (REPRODUCTION). 


607 


elasticity  is  useful  for  bending  the  lead  plate  on  the  free-lying 
places. 

Such  an  intermediate  layer  may  appropriately  consist  of  a 
number  of  layers  of  paper.  Such  a  layer,  by  reason  of  the 
character  of  the  paper  fiber  itself,  as  well  as  of  the  intermediate 
layer  of  air,  is  soft  and  elastic  as  regards  the  direction  vertical 
to  the  impression -plane,  while  on  the  other  hand  the  texture 
of  the  paper-stuff  affords  the  necessary  checks  in  the  direction 
parallel  to  the  impression-plane  to  prevent,  after  the  com- 
mencement of  pressure,  the  lateral  yielding  of  the  interme- 
diate layer.  The  latter  important  property  was  in  former 
experiments  neutralized  by  moistening  the  paper. 

In  Fig.  144  the  platen  has  sunk  so  that  the  intermediate 

FIG.  144. 


layer  opposite  to  the  places  o  o',  from  which  the  first  counter, 
pressure  emanates,  is  compressed  to  one-half  of  its  original 
volume.  At  the  moment  when  the  intermediate  layer  has  by 
compression  acquired  the  degree  of  hardness  of  the  moulding 
material,  it  is  forced  by  the  next  increase  in  pressure  into  the 
small  depressions  of  the  plane  o  o'.  On  the  places  opposite  to 
u  ur <  the  lead,  which  lies  here  perfectly  free,  and  hence  exerts 
no  counter-pressure,  is  at  the  same  time  pressed  into  the  hol- 
low space  u  uf  by  the  resisting  force  of  the  intermediate  layer. 
The  same'  is  also  the  case  opposite  to  the  places  m  w',  but 
the  bending  takes  place  in  a  less  degree,  just  as  a  board  rest- 
ing upon  supports  6  feet  apart  is  more  bent  by  a  weight  than 
one  whose  supports  are  only  3  feet  apart. 


608  ELECTRO-DEPOSITION    OF    METALS. 

This  also  answers  technical  requirements,  since  the  white 
portions  smear  the  more  readily  in  the  press,  the  greater  their 
dimensions  are. 

Thus  there  had  always  been  made  the  gross  error  of  treating 
according  to  the  same  principles  which  had  proved  good  for 
wax  and  gutta-percha,  a  body,  such  as  lead,  of  an  entirely 
different  physical  character.  The  process  of  pressing  had  in 
the  main  to  be  excluded,  and  a  bending  process  substituted 
for  it.  This  was  rendered  possible  by  a  suitable  thickness  of 
the  moulding  material,  and  by  backing  it  with  a  soft  and 
yielding  body,  which,  as  regards  its  extensibility  parallel  to 
the  impression-plane,  was  checked  by  its  texture  or  otherwise. 

By  this  bending  process  the  pressure  required  for  impres- 
sion was  under  certain  circumstances  reduced  to  one-tenth  of 
its  former  magnitude,  so  that  metal  matrices  could  also  be 
produced  from  wood-cuts  and  composition. 

This  reduction  in  pressure  is  least  manifest  with  printing 
forms  with  many  very  fine  and  crowded  printing  elements,  for 
instance,  autotypes,  for  which,  according  to  the  character  of 
the  picture,  a  pressure  of  500  to  1000  kilogrammes  per  square 
centimeter  is  required  ;  this  is  more  than  hitherto  used  for 
wax  and  gutta-percha. 

The  problem  of  the  production  of  metal  matrices  was  thus 
solved  only  for  forms  of  moderate  size,  since,  although  the 
pressure  had  been  largely  reduced  by  the  selection  of  a  correct 
thickness  of  the  lead  plate  and  by  backing  the  latter  with  a 
soft,  elastic  body,  it  was  nevertheless  much  greater  than  that 
required  for  wax  and  gutta-percha.  The  ordinary  hydraulic 
presses,  with  some  few  hundred  atmospheres,  were  therefore 
not  available  for  impressing  larger  forms. 

By  the  use  of  successive  partial  pressure  with  the  simultan- 
eous introduction  of  side-pressure,  Dr.  Albert  has  succeeded  in 
increasing,  at  a  small  expense,  about  twenty  times  the 
capacity  of  every  press  now  in  use. 

The  gradual  progression  of  a  limited  pressure  over  the 
entire  printing  form  also  prevents  the  extremely  troublesome 


GALVANOPLASTY    (REPRODUCTION).  609 

phenomena  appearing  in  other  methods  of  impressing,  namely, 
that  it  is  impossible  for  the  process  of  impression  being  affected 
by  occluded  air,  the  latter  having  at  any  time  a  chance  to 
escape. 

The  impressions  being  automatically  effected,  there  is  no 
loss  of  time  worth  speaking  of  with  this  method.  Thus,  for 
instance,  only  55  seconds  were  required  for  impressing  a  form 
of  the  "  Woche,"  and  not  quite  two  minutes  for  one  of  the 
"  Berliner  Illustrierte  Zeitung."  For  impressing  illustration- 
forms  of  the  same  size  without  letters,  only  half  the  above- 
mentioned  time  was  necessary. 

Thus  there  is  no  difficulty  whatever  in  executing  impres- 
sions of  any  size. 

Fischer  endeavors  to  attain  the  same  object  as  Dr.  Albert  by 
the  use  of  lead  plates  with  corrugated  backs,  small  pyramids 

^\AA/^  aDout  2  to  3  millimeters  high  being  thus  formed. 

These  corrugations  act  like  Albert's  elastic  intermediate  layer 
in  so  far  that  the  lead  plates  are  not  pressed,  but  bent,  into 
the  deep  portions  of  the  printing  form,  a  reduction  in  the 
otherwise  high  pressure  required  being  thus  effected.  Now, 
suppose  in  Fig.  144,  instead  of  an  elastic  intermediate  layer, 
a  lead  plate  with  corrugated  back  is  placed  upon  the  form, 
the  small  pyramids  which  are  opposite  to  the  portion  o  or  of 
the  printing  form  are  first  compressed,  while  the  part  of  the 
lead  plate  corresponding  to  the  portion  u  u'  is  bent  through 
by  the  pressure  exerted  by  the  platen  upon  the  points  of  the 
corrugations,  the  latter  being  thereby  not  very  much  flattened. 
If  now  the  pressure  be  increased  the  lead  plate  is  first  flattened 
at  o  o',  and  then  the  actual  impression,  i.  e.,  pressing  the  lead 
into  the  design  of  the  original  or  into  the  composition  begins. 
Kunze  does  not  use  corrugated  lead  plates,  but  provides  the 
platen  with  corrugations,  and  combines  therewith  a  process  of 
successive  partial  pressure  invented  by  him.  (German  patent 
applied  for.)  As  the  patent  has  not  yet  been  granted,  details 
of  the  process  cannot  be  given. 
39 


610  ELECTRO-DEPOSITION    OP    METALS. 

3.  Further  manipulation  of  the  moulds. — The  moulds  when 
detached   from  the  original  show  in  addition  to  the  actual 
impression  certain  inequalities  which  have  to  be  removed. 

With  gutta-percha  moulds  such  inequalities  in  the  shape  of 
elevations,  are  carefully  pared  away  with  a  sharp  knife,  while 
with  wax  moulds  they  are  melted  down.  For  this  purpose 
serves  a  brass  tube  about  4  inches  long,  drawn  out  to  a  fine 
point  and  connected  by  means  of  a  rubber  tube  with  a  gas 
jet.  By  opening  the  gas-cock  more  or  less,  the  gas  burns  with 
a  larger  or  smaller  pointed  flame,  and  the  brass  tube  is  guided 
by  the  hand,  so  that  the  elevations  are  melted  down  and  the 
deeper  portions  of  the  electrotype  will  present  a  smooth  ap- 
pearance. A  more  modern  instrument  for  this  purpose  is  so 
arranged  that  the  flame  can  be  regulated  by  the  finger  pres- 
sing upon  a  rubber  bulb.  However,  not  only  the  inequalities 
are  melted  down,  but  the  upper  edges,  of  the  steep  contours  of 
the  impression  are  melted  together,  and  melted  wax  is  built 
up  all  around  in  order  to  enlarge  the  depressions  in  the  elec- 
trotype and  avoid  cutting.  The  wax  is  readily  built  up  by 
holding  in  one  hand  a  thin  stick  of  wax  at  a  distance  of  about 
0.19  inch  from  the  edge  of  the  impression  and  at  about  the 
same  distance  above  the  mould,  and  melting  off  the  wax, 
drop  by  drop,  by  means  of  a  pointed  flame  guided  by  the 
other  hand.  One  drop  is  placed  close  alongside  the  other,  and 
when  the  entire  edge  of  wax  is  thus  completed  it  is  made 
perfectly  smooth  by  again  melting  with  the  pointed  flame. 

The  next  process  is 

4.  Making  the  moulds  conductive,  without  which  a  galvano- 
plastic  deposit  would   be  impossible.     Black-lead    is   almost 
exclusively  used  for  this  purpose,  and  must  be  of  the  purest 
quality  and  in  a  most  minute  state  of  division.     The  best 
material  for  this  purpose  is  prepared  from  the  purest  selected 
Ceylon  graphite,  which  is  ground  by  rolling  with  heavy  iron 
balls  until  it  is  reduced  to  a  dead  black,  impalpable  powder. 

Black-leading  the  moulds  is  performed  either  by  hand  or 
more  commonly  by  machines. 


GALVANOPLASTY    (REPRODUCTION). 


611 


Fig.  145  shows  one  of  these  machines  with  its  cover  re- 
moved to  exhibit  its  construction.  It  has  a  traveling  carriage 
holding  one  or  more  forms,  which  passes  backward  and  for- 
ward, under  a  laterally  vibrating  brush.  Beneath  the  machine 


FIG.  145. 


is  placed  an  apron  which  catches  the  powder,  which  is  again 
used. 

Another  construction  of  a  black-leading  machine  is  shown 
in  Fig.  146,  the  details  of  which  will  be  understood  without 
lengthy  description.  The  moulds  are  placed  upon  the  slowly 
revolving,  horizontal  wheel,  upon  which  the  brush  moves 
rapidly  up  and  down  with  a  vertical,  and  at  the  same  time 


612  ELECTRO-DEPOSITION    OF    METALS. 

lateral,  vibrating  motion.  The  black-leading  space  being 
closed  air-tight,  scattering  of  black-lead  dust  is  entirely  pre- 
vented, the  excess  of  .black-lead  collecting  in  a  vessel  placed 
in  the  pedestal. 

On  account  of  the  dirt  and  dust  caused  by  the  dry  process 
of  black-leading,  some  electrotypers  prefer  the  wet  process 
as  it  is  claimed  to  work  more  quickly  and  neatly,  producing 
moulds  that  are  thinly,  evenly  and  perfectly  covered. 

FIG.  146. 


moulds  are  placed  upon  a  shelf  in  a  suitable  receptacle,  and  a 
rotary  pump  forces  an  emulsion  of  graphite  and  water  over 
their  surface  through  a  traveling  fine  rose-nozzle. 

Black-leading  machines  have  recently  been  introduced,  their 
action  being  based  upon  the  principle  of  the  blast.  The  graph- 
ite powder  is  by  means  of  a  current  of  strongly-compressed 
air  carried  with  considerable  force  towards  the  surface  of  th& 
mould  to  be  black-leaded.  The  process  of  making  the  moulds 


GALVANOPLASTY  (REPRODUCTION).  613 

conductive  according  to  this  system,  is  claimed  to  be  thorough 
and  complete  and  quickly  accomplished.  However,  many 
operators  prefer  black-leading  by  hand,  especially  moulds  of 
autotypes,  the  lines  remaining  sharper. 

5.  Electrical  contact. — The  black-leaded  moulds  have  now  to 
be  provided  with  contrivances  for  conducting  the  current  upon 
the  black-leaded  surface. 

With  gutta-percha  moulds,  the  edges  are  trimmed  off  to 
within  0.19  to  0.31  inch  of  the  impression.  In  two  places  on 
the  edges  of  the  mould  holes  are  made  by  means  of  an  awl. 
Through  these  holes  stout  copper  wires  doubled  together  are 
drawn,  so  that  after  twisting  them  together  they  lie  firmly  on 
the  edge  of  the  mould.  These  wires  serve  for  suspending  the 
mould  to  the  conducting  rod,  and  previous  to  twisting  them 
together,  two  fine  copper  wires,  the  so-called  feelers,  are  placed 
between  them  and  the  e'dge  of  the  mould.  The  object  of  these 
thin  wires  being  to  effect  the  conduction  of  the  current  to  the 
lower  portions  of  the  mould,  they  must  be  firmly  secured  in 
twisting  together  the  suspension-wires. 

However,  before  allowing  these  feelers  to  rest  upon  the 
black-leaded  surface,  the  place  of  contact  of  the  wire  with  the 
mould  is  again  thoroughly  brushed  with  black-lead,  in  order 
to  be  sure  that  the  current  will  not  meet  with  resistance  on 
these  points.  With  very  large  moulds  it  is  advisable  to  use 
more  than  two  feelers  and  to  arrange  them  especially  in 
deeper  depressions.  The  thickness  of  the  feelers  should  be 
about  that  of  horse-hair. 

No  black-lead  should  get  on  the  edges  or  back  of  the  mould, 
otherwise  copper  would  also  be  deposited  on  them. 

In  place  of  the  wires  for  suspending  the  mould,  the  method 
for  wax  moulds  described  below  may  also  be  applied,  a  small, 
hot  copperplate  being  melted  in  on  the  edge  of  the  mould  and 
the  latter  secured  to  the  conducting  rod  by  means  of  a  hook. 

Gutta-percha  moulds,  being  specifically  lighter  than  the 
copper  bath,  would  float  in  it,  and  have,  therefore,  to  be 
loaded  by  securing  heated  pieces  of  lead  to  the  backs. 


614 


ELECTRO-DEPOSITION    OF    METALS. 


FIG.  147. 


For  black-leaded  wax  moulds  the  process  is  as  follows :  A 
bright  copper  plate  about  1.18  inches  square  and  0.039  inch 
thick  is  melted  in  on  the  upper  edge  of  the  mould,  and  the 
edges  are  leveled  by  means  of  a  pointed  flame,  so  as  to  pro- 
duce a  smooth  joint  between  the  copper  plate  and  wax  surface. 
This  place  is  again  thoroughly  black-leaded  with  the  hand,  and 
the  edges,  having  been  first  beveled,  are  then  melted  together 
with  the  flame.  The  wax  over  the  hole  in  the  lead  plate 
through  which  the  hook  of  the  mould-holder  is  pushed  is 
finally  removed  with  a  knife.  The  shape  of  the  mould- 
holder  is  shown  in  the  accompanying  illustration,  Fig.  147. 
The  hook  to  which  the  mould  is  suspended  is  insulated  from 
the  rest  of  the  holder  by  hard  rubber  plates,  and  the  screw- 
threads  by  hard  rubber  boxes,  so  that  the 
lead  plate  which  comes  in  contact  with  the 
hook  receives  no  current,  and  no  copper  can 
deposit  upon  it.  The  small,  square  block 
cast  on  the  holder  lies  perfectly  level  upon 
the  copper  plate  in  the  mould,  a  good  and 
abundant  conduction  of  current  being  thus 
effected,  such  as  is  absolutely  required,  for 
instance,  for  rapid  galvanoplasty. 

To  prevent  the  copper  deposit  from  spread- 
ing much  beyond  the  impression  towards  the 
edge,  it  has  been  proposed  to  cover  these 
portions  of  the  mould  with  strips  of  glass, 
hard  rubber,  or  celluloid.  For  this  purpose 
heated  glass  strips,  0.15  inch  wide  and  0.19 
inch  high,  are  pressed  about  0.079  inch  deep  into  the  wax 
mould  so  as  to  form  a  closed  frame  around  the  impression. 
Strips  of  hard  rubber  or  celluloid  of  the  above-mentioned 
width  and  height,  are  fastened  together  with  copper  pins. 
By  these  means  the  object  in  view  is  perfectly  attained. 

With  very  deep  forms  of  type,  it  is  sometimes  of  advantage 
to  first  coat  the  black-leaded  surface  with  copper,  in  order  to 
obtain  a  uniform  deposit  in  the  bath.  The  process  is  as  fol- 


GALVANOPLASTY  (REPRODUCTION).  615 

lows :  Pour  alcohol  over  the  black-leaded  form,  let  it  run  off, 
and  then  place  the  form  horizontally  over  a  water  trough. 
Now  pour  over  the  form  blue  vitriol  solution  of  15°  to  16°  B6., 
dust  upon  it  from  a  pepper-box  some  impalpable  fine  iron 
filings  and  brush  the  mixture  over  the  whole  surface,  which 
thus  becomes  coated  with  a  thin,  bright,  adherent  film  of 
copper.  Should  any  portion  of  the  surface  after  such  treat- 
ment remain  uncoppered,  the  operation  is  repeated.  The  ex- 
cess of  copper  is  washed  off  and  the  form,  after  being  provided 
with  the  necessary  conducting  wires,  is  ready  for  the  bath. 

Gilt  or  silvered  black-lead  is  also  sometimes  used  for  very 
deep  forms.  It  is,  however,  cheaper  to  mix  the  black-lead 
with  £  its  weight  of  finest  white  bronze  powder  from  finely 
divided  tin.  When  forms  thus  black-leaded  are  brought  into 
the  copper  bath,  the  particles  of  tin  become  coated  with 
copper,  also  causing  a  deposit  upon  the  black-lead  particles  in 
contact  with  them. 

6.  Suspending  the  mould  in  the  bath.     Previous  to  suspend- 
ing the  mould  in  the  copper  bath,  it  has  to  be  perfectly  freed 
from  every  particle  of  black   lead  which  might  give  rise  to 
defects  in  the  deposit. 

Strong  alcohol  is  then  poured  over  the  mould,  the  object  of 
this  being  to  remove  any  traces  of  greasy  impurities,  which  are 
readily  dissolved  and  removed  by  the  alcohol.  Moulds  thus 
treated  at  once  become  uniformly  wet  in  the  bath,  which,  if 
this  precaution  be  omitted,  is  not  the  case,  and  causes  an 
irregular  formation  of  the  deposit  (by  air-bubbles). 

The  moulds  are  suspended  in  the  bath  in  the  manner  above 
described,  special  attention  being  paid  to  having  them  hang 
parallel  to  the  anodes  so  that  all  portions  of  them  may  receive 
a  uniform  deposit. 

Before  being  suspended  in  the  bath,  the  backs  of  lead  mat- 
rices should  be  provided  with  a  protecting  layer  of  celluloid  or 
other  suitable  material  to  prevent  them  from  becoming  cop- 
pered. 

7.  Detaching  the  deposit  or  shell  from  the  mould,     a.  From 


616 


ELECTRO-DEPOSITION    OF    METALS. 


gutta-percha  moulds.  When  the  mould  has  acquired  a  deposit 
of  sufficient  thickness,  it  is  taken  from  the  bath,  rinsed  in  water, 
and  all  edges  which  might  impede  the  detachment  of  the  de- 
posit from  the  mould  are  removed  with  a  knife.  The  deposit 
is  then  gradually  lifted  by  inserting  under  one  corner  a  flat 
horn  plate,  or  a  thin  dull  brass  blade,  and  applying  a  very 
moderate  pressure.  Particles  of  gutta-percha  which  may  still 
adhere  to  the  deposit,  are  carefully  burnt  off  over  a  flame, 
b.  From  wax  moulds.  Wax  moulds  are  placed  level  upon 

Fig.  148. 


a  table,  and  hot  water  is  several  times  poured  over  them.  By 
pushing  the  finger-nail  under  one  corner  of  the  deposit,  it  can 
readily  and  without  bending  be  detached  from  the  softened 
wax.  If  not  successful  at  first,  continue  pouring  hot  water 
over  the  mould  until  the  deposit  can  be  detached  without 
difficulty. 

In  larger  establishments,  a  cast-iron  moulding  and  melting 
table,  such  as  is  shown  in  Fig.  148,  is  used  for  wax  moulds. 
The  planed  table  plate  is  hollow,  and  by  means  of  tongues 


GALVANOPLASTY  (REPRODUCTION).  617 

cast  to  the  plate  the  steam  which  is  introduced  is  forced  to 
uniformly  heat  the  entire  plate.  The  electrotypes  are  placed 
upon  the  plate,  the  wax  side  down.  The  wax  melts  and  runs 
through  stop-cocks  on  the  side  into  a  jacketed  copper  kettle, 
which  can  be  heated  by  steam  for  melting  the  wax.  The  iron 
ledges  screwed  upon  the  table  plate  are  made  tight  with  as- 
bestos paper,  so  that  the  wax  cannot  run  off  except  through 
the  stop-cocks. 

If  the  table  is  to  be  used  for  moulding  the  wax  plates,  cold 
water,  instead  of  steam,  is  allowed  to  circulate  through  the 
hollow  table  plate,  whereby  rapid  congealing  of  the  wax  is 
effected. 

Two  such  kettles  are  required,  since  the  wax  which  has  been 
in  contact  with  the  bath  has  to  be  for  several  hours  heated  in 
one  of  the  kettles  to  render  it  free  from  water  before  it  can  be 
again  used  for  moulding.  The  wax  freed  from  water  is  brought 
into  the  kettle  and  used  for  moulding  wax  plates. 

c.  From  metal-matrices.  If  the  matrix  has  been  free  from 
fat,  the  deposit  adheres  very  firmly,  and  cannot  be  lifted  off 
in  the  ordinary  manner  as  with  gutta-percha  matrices ;  nor 
can  the  deposit  be  separated  from  the  lead  by  melting  the 
latter,  as  with  the  temperature  required  for  this  purpose,  the 
copper  shell  might  be  damaged. 

Albert  found  that  by  allowing  the  metal  matrix  together 
with  the  copper  deposit  to  float  upon  readily  fusible  metallic 
alloys  with  many  free  calories,  the  deposit,  in  consequence  of 
the  unequal  expansion  of  the  metals,  can  completely  and 
without  injury  be  separated.  By  detaching  the  deposit  in 
this  manner,  Albert  succeeded  in  using  the  lead  matrix  freed 
from  the  deposit  four  times  for  the  preparation  of  electros,  the 
last  electro  thus  made  being  not  inferior  in  quality  to  the 
first  one.* 

8.  Backing  the  deposit  or  shell.  The  face  of  the  electro  is 
first  freed  from  all  residues  by  careful  burning  off  over  a  flame 

*Dr.  E.  Albert,  "  Zur  Theorie  und  Praxis  der  Metall-Matrize,"  p.  10. 


618  ELECTRO-DEPOSITION    OP    METALS. 

and  washing  with  benzine,  and  scoured  bright  with  whiting 
and  hydrochloric  acid.  The  edges  are  then  trimmed  with 
shears  to  the  width  of  a  finger  from  the  picture.  The  tinning 
of  the  back  of  the  shell  is  the  next  operation,  and  has  for  its 
object  the  strengthening  of  the  union  between  the  shell  and 
the  backing  metal.  For  this  purpose  the  back  of  the  shell  is 
cleansed  by  brushing  with  "  soldering  fluid,"  made  by  allow- 
ing hydrochloric  acid  to  take  up  as  much  zinc  as  it  will  dis- 
solve, and  diluting  with  about  one-third  of  water,  to  which 
some  ammonium  chloride  is  sometimes  added.  Then  the 
shell,  face  down,  is  heated  by  laying  it  upon  an  iron  soldering 
plate,  floated  upon  a  bath  of  melted  stereotype  metal,  and, 
when  hot  enough,  melted  solder  (half  lead  and  half  tin)  is 
poured  over  the  back,  which  gives  it  a  clean,  bright  metallic 
covering.  Or  the  shell  is  placed  downward  in  the  backing- 
pan,  brushed  over  the  back  with  the  soldering  fluid,  alloyed 
tinfoil  spread  over  it,  and  the  pan  floated  on  the  hot  backing 
metal  until  the  foil  melts  and  completely  covers  the  shell. 
When  the  foil  is  melted  the  backing-pan  is  swung  on  to  a 
leveling  stand,  and  the  melted  backing  metal  is  carefully 
poured  on  the  back  of  the  shell  from  an  iron  ladle,  commenc- 
ing at  one  of  the  corners  and  gradually  running  over  the  sur- 
face until  it  is  covered  with  a  backing  of  sufficient  thickness. 
Another  method  is  as  follows :  After  tinning  the  shell  it  is 
allowed  to  take  the  temperature  of  the  backing  metal  on  the 
floating  iron  plate.  The  plate  is  then  removed  from  the  melted 
metal,  supported  in  a  level  position  on  a  table  having  project- 
ing iron  pins,  on  which  it  is  rested,  and  the  melted  stereotype 
metal  is  carefully  ladled  to  the  proper  thickness  on  the  back 
of  the  tinned  shell.  This  process  is  called  "  backing."  The 
thickness  of  the  metal  backing  is  about  an  eighth  of  an  inch. 
A  good  composition  for  backing  metal  consists  of  lead  90  parts, 
tin  5  and  antimony  5.  An  alloy  of  lead  100  parts,  tin  3  and 
and  antimony  4  is  also  recommended  as  very  suitable. 

9.  Finishing. — For  this  purpose  the  plates  go  first  to  the  saw 
table  (Fig.  149)  for  the  removal  of  the  rough  edges  by  means 


GALVANOPLASTY  (REPRODUCTION). 


619 


of  a  circular  saw.  The  plates  are  then  shaved  to  take  off  any 
roughness  from  the  back  and  make  them  of  even  thickness. 
In  large  establishments  this  portion  of  the  work,  which  is  very 
laborious,  is  done  with  a  power  planing  or  shaving  machine, 
types  of  which  are  shown  in  Figs.  150  and  151,  Fig.  150  being 
a  shaving  machine  with  steam  one  way,  and  Fig.  151  one 
with  steam  both  ways.  By  means  of  a  straight-edge,  the 

FIG.  149. 


plates  are  then  tested  as  to  their  being  level,  and  any  un- 
eveness  is  rectified  by  gentle  blows  with  a  polished  hammer, 
care  being  taken  not  to  damage  the  face.  The  plate  then 
passes  to  the  hand-shaving  machine,  where  the  back  is  shaved 
down  to  the  proper  thickness,  smooth  and  level.  The  edges 
of  the  plate  are  then  planed  down  square  and  to  a  proper 
size,  and  finally  the  plates  are  mounted  on  wood  type-high. 


620  ELECTRO-DEPOSITION    OF    METALS. 

Book-work  is  generally  not  mounted  on  wood,  the  plates 
being  left  unmounted  and  finished  with  beveled  edges,  by 
which  they  are  secured  on  suitable  plate-blocks  of  wood  or 
iron  supplied  with  gripping  pieces,  which  hold  them  firmly 
at  the  proper  height,  and  enable  them  to  be  properly  locked  up. 

FIG.  150. 


Copper  deposits  from  metallic  surfaces. — It  remains  to  say  a 
few  words  about  the  process,  by  which  a  copy  may  be  directly 
made  from  a  metallic  surface  without  the  interposition  of  wax 
or  gutta-percha.  If  the  metallic  surface  to  be  moulded  were 
free  from  grease  and  oxide,  the  deposit  would  adhere  so  firmly 
as  to  render  its  separation  without  injury  almost  impossible. 


GALVANOPLASTY  (REPRODUCTION). 


621 


Hence,  the  metallic  original  must  first  undergo  special  prepa- 
ration, so  as  to  bring  it  into  a  condition  favorable  to  the  detach- 
ment of  the  deposit.  This  is  done  by  thoroughly  rubbing  the 
original  with  an  oily  rag,  or,  still  better,  by  lightly  silvering  it 
and  exposing  the  silvering  for  a  few  minutes  to  an  atmosphere 
of  sulphuretted  hydrogen,  whereby  silver  sulphide  is  formed, 
which  is  a  good  conductor,  but  prevents  the  adherence  of  the 
deposit  to  the  original.  For  the  purpose  of  silvering,  free  the 

FIG.  151. 


surface  of  the  metallic  original  (of  brass,  copper,  or  bronze) 
from  grease,  and  pickle  it  by  washing  with  dilute  potassium 
cyanide  solution  (1  part  potassium  cyanide  to  20  water). 
Then  brush  it  over  with  a  solution  of  4J  drachms  of  silver 
nitrate  and  1  oz.  6  drachms  of  potassium  cyanide  (98  per  cent.) 
in  one  quart  of  water ;  or,  still  better,  immerse  the  original  for 
a  few  seconds  in  this  bath,  until  the  surface  is  uniformly  coated 
with  a  film  of  silver.  The  production  of  the  layer  of  silver  sul- 


622  ELECTRO-DEPOSITION    OF    METALS. 

phide  is  effected  according  to  the  process  described  later  on. 
The  negative  thus  obtained  is  also  silvered,  made  black  with 
sulphuretted  hydrogen,  and  a  deposit  of  copper  is  then  made, 
which  represents  an  exact  copy  of  the  original.  Instead  of 
sulphurizing  the  silvering  with  sulphuretted  hydrogen,  it  may 
also  be  iodized  by  washing  with  dilute  solution  of  iodine  in 
alcohol.  The  washed  plate,  prior  to  bringing  it  into  the 
copper  bath,  is  for  some  time  exposed  to  the  light. 

To  prevent  the  reduction  of  copper  on  the  back  of  the 
metallic  original  to  be  copied,  it  is  coated  with  asphalt  lacquer, 
which  must  be  thoroughly  dry  before  bringing  into  the  bath. 
When  the  deposit  of  copper  is  of  sufficient  thickness,  the  plate 
is  taken  from  the  bath,  rinsed  in  water,  and  dried.  The  edges 
are  then  trimmed  off  by  filing  or  cutting  to  facilitate  the  sepa- 
ration of  the  shell  from  the  original. 

Of  course  only  metals  which  are  not  attacked  by  the  acid 
copper  solution  can  be  directly  brought  into  the  bath.  Steel 
plates  must  therefore  first  be  thickly  coppered  in  the  alkaline 
copper  bath,  and  even  this  precaution  does  not  always  protect 
them  from  corrosion.  It  is  therefore  better  to  produce  in  a 
silver  bath  (formula  I.,  p.  368)  a  copy  in  silver  of  sufficient 
thickness  to  allow  of  the  separation  of  both  plates.  The  silver 
plate  is  iodized,  and  from  it  a  copy  in  copper  is  made  by  the 
galvanoplastic  process.  The  copper  plate  thus  obtained  is  an 
exact  copy  of  the  original,  and  after  previous  silvering,  the 
desired  number  of  copies  may  be  made  from  it. 

Other  operations  which  may  have  to  be  done  in  galvano- 
plastic plants,  for  instance,  coppering  of  zinc  etchings,  and  of 
stereotypes,  and  nickeling  and  cobalting  the  latter,  as  well  as 
electrotypes,  have  already  been  described  in  the  part  devoted 
to  electro-plating,  so  that  few  words  will  here  suffice. 

Stereotypes  are,  as  a  rule,  coppered  in  the  acid  copper  bath, 
stereotype  metal  being  not  attacked  by  it.  The  bath,  how- 
ever, should  not  have  a  large  content  of  free  sulphuric  acid. 
In  order  to  have  the  copper  adhere  well  the  plates,  previous 
to  being  brought  into  the  bath  must,  of  course,  be  thoroughly 


GALVANOPLASTY  (REPRODUCTION).  623 

freed  from  grease  by  brushing  with  warm  soda  solution  and 
whiting. 

Zinc  plates  are  thoroughly  freed  from  grease,  and  then  cop- 
pered or  brassed.  Nickeling  is  effected  according  to  the  pro- 
cess given  under  "  Deposition  of  Nickel." 

Preparation  of  type-matrices. — The  process  varies  according 
to  whether  the  originals  consist  of  zinc  or  of  a  material  (lead- 
antimony-bismuth  alloy)  indifferent  towards  the  acid  copper 
bath. 

It  is  best  to  brass  zinc  originals,  and  to  give  the  brass  de- 
posit higher  lustre  by  polishing  with  Vienna  lime  powder 
upon  a  small  flannel  bob.  They  are  then  freed  from  grease 
by  brushing  with  quicklime,  silvered  by  the  method  previously 
given,  and  iodized.  The  surfaces  which  are  to  remain  free 
from  deposit  are  stopped  off  with  wax,  and  the  originals 
placed  in  the  acid  copper  bath,  care  being  taken  to  bring 
them  in  contact  with  the  current-carrying  conducting  rod  be- 
fore immersion  in  the  bath. 

Originals  of  hard  lead  or  similar  alloys,  after  having  been 
suitably  prepared,  may  be  directly  suspended  in  the  copper 
bath,  since  a  heavy  copper  deposit  can  be  quite  readily  de- 
tached' from  them,  though  slightly  oiling  them  will  do  no 
harm. 

The  current-density  for  depositing  must  be  slight  to  prevent 
formation  of  buds.  The  deposit  is  generally  made  0.079  to 
0.098  inch  thick,  when  it  is  detached  from  the  original,  and 
after  filing  the  edges  backed  with  zinc  or  brass.  The  matrix 
is  finally  justified. 

Regarding  nickel  matrices,  see  "  Galvanoplasty  in  Nickel." 

Electro-etching. — It  is  in  place  here  to  discuss  the  process  of 
electro-etching,  it  being  chiefly  applied  in  the  graphic  indus- 
tries, and  a  few  methods  of  etching,  which  are  not  executed 
by  electrical  means,  will  first  be  referred  to. 

Methods  of  dissolving  the  various  metals  by  acids  were 
probably  known  many  centuries  ago,  it  being  beyond  doubt 
shown  by  the  notable  productions  of  the  goldsmiths,  as  well  as 


624  ELECTRO-DEPOSITION    OF    METALS. 

of  the  armorers,  about  the  year  1400,  that  they  possessed*  a 
knowledge  of  etching.  It  may  also  be  supposed  that  the 
niello  work  of  the  goldsmiths  was  the  forerunner  of  copper 
engraving,  an  art  still  highly  appreciated  at  the  present  day, 
and  the  earliest  impression  of  which  dates  from  the  year  1446. 

There  are  four  different  methods  of  copper  engraving,  but 
that  in  which  etching  plays  an  important  role,  would  seem  to 
be  the  most  interesting. 

To  protect  separate  portions  of  metallic  surfaces  from  the 
action  of  the  acid,  a  so-called  covering  or  etching  ground  is 
used,  which  consists  of  a  mixture  of  2J  parts  asphalt,  2  parts 
wax,  1  part  rosin  and  2  parts  black  pitch,  applied  hot. 

The  copper  engraver  uses  for  his  work  another  composition 
of  resins,  and  it  is  here  given  because  this  covering  ground  has 
proved  capable  of  resisting  25  per  cent,  nitric  acid.  Yellow 
wax  4  parts,  Syrian  asphalt  4,  black  pitch  1,  and  white  Bur- 
gundy pitch  1.  Melt  the  ingredients,  and  when  the  mixture 
boils,  gradually  add,  whilst  stirring  constantly,  4  parts  more 
of  pulverized  Syrian  asphalt.  Continue  boiling  until  a  sample 
poured  upon  a  stone  and  allowed  to  cool  breaks  in  bending. 
Then  pour  the  mixture  into  cold  water  and  shape  it  into  small 
balls,  which  for  use  are  dissolved  in  oil  of  turpentine. 

Upon  a  heated  plate,  ground  perfectly  level,  the  copper  en- 
graver then  applies  the  above-mentioned  covering  ground  so 
thin  that  the  metallic  surface  appears  golden-yellow.  The 
covering  ground  is  next  blackened  by  means  of  a  wax  torch, 
and  the  outlines  of  the  picture  to  be  made  are  then  sketched. 

Now  commences  the  work  which  shows  the  artistic  talent  of 
the  engraver.  With  a  fine  etching-needle  he  scratches  the 
contours  of  the  picture  into  the  covering  ground,  without, 
however,  injuring  the  metal,  and  finishes  his  work  by  nar- 
rower and  wider  lines  until  the  desired  effect  is  believed  to  be 
produced. 

However,  to  make  this  work  fit  to  be  printed,  the  lines  of 
the  picture  must  lie  depressed  in  the  metal  plate.  For  this 
purpose  the  plate  is  surrounded  with  a  wax  rim  and  subjected 


GALVANOPLASTY  (REPRODUCTION).  625 

'  to  etching  with  nitric  acid  or,  more  recently,  with  ferric  chlo- 
ride. After  the  at  first  weak  acid  has  acted  for  a  short  time, 
the  finest  lines  have  acquired  the  required  depth.  The  fluid 
is  then  poured  off  and  the  fine  lines  are  stopped  off,  when 
etching  is  recommenced.  Thus  progressing,  a  picture  with 
lines  becoming  constantly  deeper,  as  well  as  broader,  is  formed, 
the  result  finally  showing  the  artistic  talent  of  the  engraver. 
The  plate  is  cleansed  and  handed  to  the  printer,  or  it  may  be 
steeled  or  manifolded  by  galvanoplasty. 

While  speaking  of  this  process  of  copper-engraving,  our  at- 
tention is  involuntarily  directed  to  a  very  interesting  achieve- 
ment, which  deserves  mention  in  connection  with  the  work  of 
the  etcher  and  of  the  operator  in  galvanoplasty.  The  process  is 

Photo- engraving,  by  means  of  which  copper  plates,  as  well  as 
small  and  also  very  extensive  pictures,  of  such  high  artistic 
value  can  be  produced  that  they  form  at  present  an  important 
branch  of  the  art  business. 

Former  investigators  have  shown  : 

1.  That  of  all  the  varieties  of  glue,  gelatine  possesses  the 
greatest  swelling  capacity. 

2.  That  when  mixed  with  potassium   dichromate  and  ex- 
posed to  the  action  of  light,  gelatine  becomes  insoluble,  i.  e., 
it  loses  entirely  its  power  of  swelling. 

Upon  this  is  based  the  following  process :  Take  a  sheet  of 
well-sized  paper  and  make  a  rim  around  it,  about  0.39  inch 
high,  by  turning  up  the  sides.  The  paper  thus  prepared, 
which  now  forms  a  sort  of  dish,  is  placed  upon  a  perfectly 
level  surface  and  a  solution,  consisting  mostly  of  gelatine  col- 
ored black,  is  poured  over  it.  Such  paper  is  found  in  com- 
merce under  the  name  of  black  pigment  paper.  It  is  immersed 
in  solution  of  ammonium  dichromate,  dried  in  a  dark  room 
and  stored  for  use. 

A  perfect  diapositive  of  the  original  is  placed  in  a  copying 
frame  and,  after  covering  it  with  the  prepared  pigment  paper, 
the  frame  is  closed. 

By  the  rays  of  light  which  strike  the  prepared  paper  through 
40 


626  ELECTRO-DEPOSITION    OF    METALS. 

the  diapositive,  the  layer  of  chromium  and  gelatine  is  hard- 
ened, the  process  taking  place  in  the  same  gradations  of  tone 
as  conditioned  by  the  diapositive.  After  sufficient  exposure  to 
the  light,  the  pigment  paper  is  placed  in  a  water  bath  and  a 
quite  perceptible  picture  in  relief  will  in  a  short  time  appear. 
The  portions  which  had  not  been  exposed  to  the  light,  swell 
up  very  much  and  lose  the  greater  part  of  the  coloring  matter 
mixed  with  the  gelatine.  The  result  is,  therefore,  the  reverse 
of  the  diapositive  used. 

By  means  of  an  ingenious  contrivance,  a  layer  of  impalpable 
asphalt  powder  has  in  the  meanwhile  been  applied  to  a  finely 
ground  copper-plate,  and  melted  upon  it.  The  above-men- 
tioned chrome-gelatine  picture  is  now  placed  upon  the  plate 
and  is  made  to  adhere  by  rubbing.  The  paper  can  now  be 
readily  detached,  while  the  picture  adheres  to  the  copper- 
plate. The  gelatine-layer  forms  the  protection  from  the  effect 
of  the  etching  with  ferric  chloride. 

It  will  be  readily  understood  that  for  this,  and  all  the  pre- 
ceding manipulations,  great  skill  and  years  of  experience  are 
required  in  order  to  produce  such  results  as  we  have  occasion 
to  admire  in  the  art  stores. 

If  galvanoplasty  is  to  be  employed  for  the  production  of 
such  copper-plates,  a  glass  or  metal  plate  is  used  and  coated 
with  the  chrome-gelatine  above  described.  It  is  then  exposed 
to  the  light  under  a  photographic  glass  negative,  allowed  to 
swell  up,  and  for  a  short  time  laid  in  a  weak  chrome  alum 
solution.  The  layer  is  then  so  hard  as  to  allow  of  making  a 
wax  mould  and  an  electrotype.  The  process  is  called  photo- 
galvanography. 

The  swelling  power  of  gelatine,  as  well  as  its  insolubility, 
has  led  to  the  production  of  collographic  printing.  The  man- 
ipulations for  the  preparation  of  the  printing  plates  required 
for  this  purpose  differ  but  little  from  those  for  photo-galvan- 
ography. 

Pour  over  a  glass  plate,  0.19  to  0.27  inch  thick,  a  layer  of 
chrome-gelatine,  which,  however,  must  not  be  colored,  and 


GALVANOPLASTY    (REPRODUCTION).  627 

place  the  plate  in  a  drying-oven  heated  to  113°  F.  The  plate 
is  then  exposed  to  the  light  under  a  photographic  negative 
and  the  layer  of  gelatine  allowed  to  swell  up. 

Another  property  shown  by  chrome-gelatine  is  that  the 
portions  which  have  become  insoluble  by  exposure  to  light 
are  very  susceptible  to  fat  colors.  If  now  such  a  glass  plate 
be  wiped  over  with  a  moist  sponge  and  then  blackened  all 
over  by  means  of  a  suitable  color  with  the  use  of  a  roller,  a 
picture  showing  all  the  details  of  the  negative  used  appears 
upon  the  glass  plate.  By  placing  upon  this  picture  a  sheet 
of  printing-paper,  and  drawing  both  through  the  collographic 
printing-press,  the  color  adheres  to  the  paper. 

An  etching  process  which  includes  all  the  improvements 
made  in  metal  etching,  and  which,  by  reason  of  the  great 
progress  made  in  photography,  has  won  a  great  field  of  activ- 
ity, is 

Zincography. — All  plates  produced  by  this  process  are  in- 
tended for  book  printing,  and  must  show  all  the  lines  and 
points  of  the  picture  in  relief,  while  the  parts  which  in  print- 
ing result  in  the  white  portions  of  the  picture  should  be  as 
deep  as  possible.  It  is  obvious  that  this  requirement  makes 
the  highest  demands  on  the  etching  process,  and  that  long 
experience  and  perseverance  are  required  to  achieve  excel- 
lency in  this  respect. 

All  former  experiments  will  here  be  omitted,  and  only  the 
process  which  has  proved  of  practical  value  will  be  described. 

Freshly-made  impressions  are  reprinted  upon  fine  zinc 
plates  ground  perfectly  level,  drawings  executed  with  suitable 
ink  upon  prepared  paper  being  used  in  the  same  manner. 

When  the  reprints  have  been  successfully  made  and  any 
defects  removed  by  retouching,  very  finely  powdered  rosin  is 
poured  upon  the  metal  plate  and  rubbed  with  a  brush  into 
the  points  and  lines  of  the  drawing.  Since  no  rosin  powder 
adheres  to  the  portions  of  the  plate  not  printed  on,  the  plate 
may  at  once  be  laid  upon  the  hot-plate  and  highly  heated. 
The  rosin  powder  combines  intimately  with  the  printing  ink, 
a  layer  which  well  resists  weak  nitric  acid  being  thus  formed. 


628  ELECTRO-DEPOSITION    OF    METALS. 

After  etching  for  a  short  time  with  dilute  nitric  acid,  fine 
silvery  edges  produced  by  the  washing  away  of  the  dissolved 
metal  appear  on  all  the  lines  and  points  of  the  reprint.  If 
etching  would  now  be  continued,  the  lines  and  points  would 
also  be  laterally  attacked  by  the  acid.  Over-etching  would 
thus  take  place,  and  all  the  fine  portions  of  the  picture  disap- 
pear. Hence  a  fresh  protecting  cover  has  to  be  applied,  which 
protects  from  corrosion,  not  only  the  surfaces  of  the  lines  and 
points,  but  also  the  above-mentioned  silvery  edges.  For  this 
purpose,  the  etcher  uses  a  lithographic  roller  and  a  suitable 
etching  color.  The  drawing  is  then  dusted  over,  and  the 
plate  heated  as  previous  to  the  first  etching.  Proceeding  in 
the  same  manner,  the  manipulations  are  repeated  until  the 
plate  has  the  necessary  depth  for  printing.  Finally,  all  un- 
necessary metal  is  cut  away  with  a  fret-saw,  and  the  etching 
having  been  mounted  on  wood,  is  ready  to  be  given  to  the 
printer. 

If,  however,  the  original  handed  in  for  reproduction,  is  to 
be  enlarged  or  reduced,  a  photographic  negative  of  it  is  first 
made  and  copied  directly  upon  the  zinc  plate.  For  this  pur- 
pose, a  coating  of  asphalt  solution,  or  of  a  mixture  of  egg  or 
glue  with  ammonium  dichromate,  is  applied  to  the  zinc  plate, 
and  the  negative  having  been  placed  upon  the  latter,  it  is  ex- 
posed to  the  light.  The  result  is  the  same  as  has  been  de- 
scribed under  photo-engraving,  a  picture  being  obtained  which 
is  exactly  treated  as  the  reprinted  drawings,  i.  e.t  powdered, 
heated,  and  etched. 

Another  process  of  transferring  is  effected  by  reprinting : 

A  sheet  of  paper  coated  with  chrome-gelatine  is  dried  in  a 
dark  room,  placed  in  a  copying  frame  under  a  negative  and 
exposed  to  the  light  until  a  beautiful,  chestnut-brown  picture 
is  perceptible.  The  chromium  salt  is  dissolved  in  the  water 
bath,  the  picture  inked  with  reprinting  ink  and,  after  drying, 
transferred  to  the  metal  plate. 

Up  till  now  we  have  only  spoken  of  points  and  lines,  be- 
cause the  originals  have  to  be  composed  of  such  to  be  suitable 


GALVANOPLASTY    (REPRODUCTION).  629 

for  the  reproduction  process.  Photography,  however,  makes 
it  also  possible  to  transform  water-color  paintings,  photo- 
graphs, India-ink  sketches,  etc.,  into  book-printing  plates. 

For  this  purpose  the  photographer  uses  a  glass  plate  pro- 
vided with  a  network  of  very  fine  lines,  places  it  between  the 
sensitive  glass  plate  and  the  original,  and  thus  produces  a  neg- 
ative, which,  though  composed  of  millions  of  small  points, 
nevertheless  gives  all  the  shadings  of  the  original.  This  pro- 
cess is  called  autotypy,  and  is  at  present  used  to  such  an  extent 
and  has  been  brought  to  such  a  state  of  perfection,  as  to  make 
it  difficult  to  say  when  the  limit  of  what  can  be  done  by  the 
etching  process  in  connection  with  photography  may  be 
reached. 

The  achievements  in  photography  widen  almost  daily  the 
field  of  activity  of  the  etcher,  and  it  may  be  anticipated  that 
printing  plates  will  in  this  manner  be  produced  which,  when 
printed  in  three  colors,  will  yield  impressions  such  as  could 
formerly  only  be  attained  by  the  lithographer  with  the  use  of 
many  stones.  It  is  by  no  means  impossible  that  the  electric 
current  may  before  long  be  utilized  in  the  execution  of  the 
above-mentioned  etching  processes,  and  for  this  reason  a  few 
hints  will  here  be  given  which  may  be  of  use  to  the  galvano- 
plastic  operator. 

In  etching  steel,  copper  or  zinc  plates,  in  the  ordinary  way, 
a  covering  ground,  as  previously  mentioned,  is  applied  to  the 
plate  to  be  etched.  The  drawing  is  then  transferred  to  the 
covering  ground  and  traced  with  the  graver,  taking  care  that 
the  tool  lays  bare  the  metal  in  all  the  lines.  A  rim  of  wax  is 
then  made  around  the  plate,  and  dilute  nitric  acid  or  another 
solution  poured  over  it.  The  basis-metal  is  attacked  by  the 
acid  and  the  drawing  is  thus  etched. 

The  injurious  acid  vapors  evolved  thereby  and  the  lateral 
corrosion  of  the  lines,  as  well  as  other  drawbacks,  have  brought 
about  the  execution  of  etching  with  the  assistance  of  the  elec- 
tric current,  the  above-mentioned  drawbacks  being  thereby 
obviated,  and  more  rapid  and  reliable  working  rendered  pos- 


630  ELECTRO-DEPOSITION    OF    METALS. 

sible.  The  plate  is  treated  in  exactly  the  same  manner  as  for 
ordinary  etching,  but  instead  of  furnishing  it  with  a  wax  rim 
and  pouring  acid  over  it,  it  is  suspended  in  a  suitable  solution 
as  anode — hence  connected  with  the  positive  pole — a  metal 
plate  of  the  same  size  connected  with  the  negative  pole  being 
suspended  parallel  to  it.  The  metal  is  dissolved  by  the  acid- 
residue  appearing  on  the  positive  pole. 

For  copper-plates  which  are  to  be  etched,  the  ordinary  acid 
copper  bath  is  used  ;  for  zinc-plates,  solution  of  zinc  sulphate  ; 
for  steel-plates,  solution  of  copperas  or  of  ammonium  chloride; 
for  brass,  solution  of  ferric  chloride.  In  place  of  the  baths  of 
metallic  salts,  pure  water  slightly  acidulated  with  sulphuric, 
hydrochloric,  or  nitric  acid  may  be  used. 

As  covering  or  etching  ground,  the  previously  mentioned 
mixture  of  rosin  and  wax,  or  the  acid-proof  varnish  is  used. 

Since  the  current-strength  is  under  perfect  control,  the  etch- 
ing may  be  carried  to  any  depth  desired.  Some  portions  may 
be  less  etched  than  others  by  taking  the  plate  from  the  bath, 
and,  after  washing  and  drying,  coating  the  portions  which  are 
not  to  be  further  etched  with  lacquer,  and  returning  the  plate 
to  the  bath. 

Printing  plates  in  relief  may  in  this  manner  be  prepared  by 
slightly  etching  the  bared  design  of  a  copper  plate  in  the  gal- 
vanoplastic  copper  bath,  and  then  bringing  the  plate  as  object 
in  contact  with  the  negative  pole,  while  a  plate  of  chemically 
pure  copper  serves  as  anode.  The  deposited  copper  unites 
firmly  with  the  rough  copper  of  the  etched  plates,  and  after 
removing  the  etching  ground  with  benzine  or  oil  of  turpentine, 
the  design  appears  in  relief. 

Heliography. — The  heliographic  process,  invented  by  Pretsch, 
and  improved  by  Scamoni,  consists  in  taking  by  photography 
a  good  negative  of  the  engraving  or  other  object  to  be  repro- 
duced, developing  with  green  vitriol,  reinforcing  with  pyrogallic 
acid  and  silver  solution,  and  then  fixing  with  sodium  hypo- 
sulphite solution  in  the  same  manner  as  customary  for  pho- 
tographic negatives.  A  further  reinforcement  with  chloride  of 


GALVANOPLASTY  (REPRODUCTION).  631 

mercury  solution  then  takes  place  until  the  layer  appears  light 
gray.  Now  wash  thoroughly  and  intensely  blacken  the  light 
portions  by  pouring  upon  them  dilute  potassium  cyanide  solu- 
tion. As  in  the  photographic  process,  the  solution  must  be 
applied  in  abundance  and  without  stopping,  as  otherwise 
streaks  and  stains  are  formed.  After  washing,  the  plate  is 
dried,  further  reinforced,  and  finally  coated  with  a  colorless 
negative  varnish.  From  this  negative  a  positive  collodion 
picture  is  taken,  which  is  in  the  same  manner  developed,  re- 
inforced and  fixed,  the  reinforcement  with  pyrogallic  acid 
being  continued  until  the  picture  is  quite  perceptibly  raised. 
After  careful  washing,  pour  upon  the  plate  quite  concentrated 
chloride  of  mercury  solution,  which  has  to  be  frequently  re- 
newed, until  the  picture,  at  first  deep  black,  acquires  a  nearly 
white  color,  and  the  lines  are  perceptibly  strengthened.  Now 
wash  with  distilled  water,  next  with  dilute  potassium  iodide 
solution,  and  finally  with  ammoniacal  water,  whereby  the 
picture  acquires  first  a  greenish,  then  a  brown,  and  finally  a 
violet-brown,  color.  After  draining,  the  plate  may  be  pro- 
gressively treated  with  solutions  of  platinum  chloride,  gold 
chloride,  green  vitriol  and  pyrogallic  acid,  the  latter  exerting 
a  solidifying  effect  upon  the  pulverulent  metallic  deposits. 
The  metallic  relief  is  now  ready ;  the  layer  is  slowly  dried 
over  alcohol,  and  the  plate,  when  nearly  cold,  quickly  coated 
with  a  thin  rosin  varnish,  which,  after  momentary  drying, 
remains  sufficiently  sticky  to  retain  a  thin  layer  of  black  lead, 
which  is  applied  with  a  tuft  of  cotton.  The  edge  of  the  plate 
is  finally  surrounded  with  wax,  and,  after  being  wired,  the 
plate  is  brought  into  the  galvanoplastic  copper  bath  to  be 
reproduced. 

Electro-engraving. — Below  an  outline  of  Rieder's  patented 
process  is  given,  it  being  supposed  that  the  subject  under  dis- 
cussion is  the  production  of  a  die  by  means  of  which  reliefs 
are  to  be  stamped  in  metal  plates. 

The  relief  is  first  produced  in  a  material  readily  worked,  for 
instance,  wood,  wax,  etc.,  and  a  copy  of  it  made  in  plaster  of 


632  ELECTRO-DEPOSITION    OF    METALS. 

Paris.  The  plaster  of  Paris  plate,  which  is  about  £  to  £  inch 
or  more  thick,  is  placed  in  a  metal  cylinder  in  such  a  manner 
that  a  plaster  of  Paris  surface  of  0.11  to  0.15  inch  depth  pro- 
jects above  the  edge  of  the  cylinder.  This  cylinder  contain- 
ing the  plaster  of  Paris  model  is  secured  in  a  vessel  containing 
solution  of  ammonium  chloride  and  a  metal  spiral  connected 
with  the  negative  pole  of  the  source  of  current.  By  a  suitable 
mechanical  contrivance  the  vessel,  together  with  the  cylinder 
containing  the  model,  is  pressed  against  the  steel  plate  con- 
nected with  the  positive  pole. 

The  process  is  now  as  follows :  The  porous  plaster  of  Paris 
absorbs  to  saturation  ammonium  chloride  solution.  The  steel 
plate  first  comes  in  contact  with  the  highest  points  of  relief, 
and  the  current  becoming  active,  dissolves  the  steel  on  the 
point  of  contact.  The  ferrous  chloride  solution  which  is 
formed  penetrates  downwards  into  the  capillaries  of  the  plaster 
of  Paris,  so  that  fresh  quantities  of  the  electrolyte  constantly 
act  upon  the  steel  plate.  Etching  thus  progresses,  and  gradu- 
ally every  portion  of  the  plaster  of  Paris  model  comes  in  con- 
tact with  the  steel  plate,  when  etching  is  finished. 

However,  the  practical  execution  of  the  work  is  not  so 
simple  as  the  theoretical  process  above  described.  The  carbon 
in  the  steel  and  other  admixtures,  such  as  silicon,  etc.,  prevent 
uniform  etching  and  must,  therefore,  from  time  to  time,  be 
mechanically  removed  from  the  etching  surface.  For  this 
purpose  the  vessel  containing  the  electrolyte,  together  with  the 
model,  has  to  be  lowered,  the  steel  plate  taken  from  the  ap- 
paratus and  cleansed.  It  will,  therefore,  be  readily  under- 
stood that  accurate  etching  corresponding  to  the  metal  can 
only  take  place  when  the  principal  parts,  namely,  the  steel 
plate  and  model,  after  cleansing,  mathematically  occupy  ex- 
actly the  same  place  and  position  as  before,  so  that  the  model 
presses  accurately  against  the  same  parts  of  the  steel  plate  as 
in  the  beginning  of  the  etching  operation. 

Conjointly  with  Dr.  Geo.  Langbein  &  Co.,  Rieder  has  con- 
structed an  apparatus  which  works  with  such  -precision  as  to 


GALVANOPLASTY    (REPRODUCTION).  633 

fulfill  all  the  above-mentioned  conditions,  and  may  be  briefly 
described  as  follows :  *  The  plaster  mould  is  secured  by  two 
conical  wedges  to  a  cast-iron  frame  upon  a  vertically  moving 
table,  the  latter  being  set  in  motion  by  an  eccentric.  Above 
this  table  is  the  clamping  plate  for  the  steel  anode  to  be  etched. 
This  clamping  plate  is  also  adjustable,  and  by  a  suitable  con- 
trivance can  be  set  exactly  parallel  to  the  model.  Cleansing 
of  the  steel  plate  is  effected  by  means  of  a  carriage  carrying  a 
revolving  brush  and  worked  by  an  eccentric  ;  the  brush  re- 
ceives water  through  a  perforated  pipe,  and  in  addition  a 
sponge  roller  is  carried  over  the  model  for  the  purpose  of 
acidulating  the  latter. 

The  machine  works  as  follows :  By  means  of  the  movable 
table  the  model  is  without  shock  and  as  elastically  as  possible 
placed  against  the  plate  to  be  etched.  After  the  plate  and 
model  have  been  in  contact  for  15  seconds,  the  model  is  lifted 
off  and  the  cleaning  process  by  brushing,  etc.,  is  effected.  As 
soon  as  the  cleaning  carriage  is  withdrawn,  the  model  is  again 
brought  against  the  steel-plate  and  the  operation  repeated. 

Each  electro-engraving  machine  is  supplied  with  a  model 
casting  arrangement,  the  frames  of  the  machine  being  utilized 
for  the  purpose. 

The  dynamo  used  has  an  impressed  electro-motive  force  of 
12  to  15  volts,  and  the  current-strength  for  a  plate  of  200  x  300 
millimeters  is  about  50  amperes,  when  the  whole  surface  of 
the  plaster  model  has  been  brought  in  contact  with  the  steel- 
plate.  An  electro-engraving  plant  of  this  kind  was  exhibited 
at  the  Paris  Exposition  in  1900. 

The  depth  of  the  etching  depends  on  the  time  of  contact, 
but  it  may  be  laid  down  as  a  rule  that,  according  to  the  fine- 
ness of  the  model  4  or  5  hours  are  required  for  a  depth  of  1 
millimeter.  The  cleaning  process  above  described  may  event- 
ually be  effected  with  the  assistance  of  an  air  compressor. 

*  Pfanhauser,   Die   Herstellung  von   Metallgegenstanden  auf  elektrolytischen 
Wege  und  die  Elektrograviire,  1903. 


634  ELECTRO-DEPOSITION    OF    METALS. 

Allowing  12  seconds  as  the  duration  of  etching,  about  600  to 
800  etching  periods  must  take  place  in  order  to  etch  to  the 
depth  of  1  millimeter.  Experiments  made  on  a  large  scale 
have  proved  this  method  to  be  very  suitable  for  many  pur- 
poses, even  if  it  does  not  make  hand-engravers  superfluous. 
For  the  latter,  however,  it  is  an  excellent  auxiliary  for  the 
purpose  of  obtaining  engravings  absolutely  true  to  nature  from 
models  in  wax,  etc.,  and  it  allows  of  the  preparation  in  a  very 
short  time  of  engraved  dies,  plates,  etc.  The  last  retouching 
and  polishing  have  to  be  done  by  the  hand  of  the  engraver, 
because  in  accordance  with  the  nature  of  the  porous  plaster- 
of-Paris  model,  the  etched  surface  shows  but  little  luster. 
Further  details  would  not  come  within  the  compass  of  this 
work,  and  interested  parties  are  referred  to  the  firm  "  Elektro- 
graviire,"  Leipsic,  Saxony,  Germany,  who  has  secured  the 
patents  and  constructs  the  electro-engraving  machines. 

B.   GALVANOPLASTIC  REPRODUCTION  OF  PLASTIC  OBJECTS. 

The  reproduction  of  busts,  vases,  etc.,  requires  an  entirely 
different  process  of  preparing  the  moulds  than  that  described 
as  applied  in  the  graphic  arts,  the  material  for  moulding  de- 
pending on  the  nature  of  the  original.  Besides  gutta-percha 
and  wax,  readily  fusible  metals,  oil  gutta-percha,  plaster  of 
Paris,  and  glue  will  have  to  be  considered.  If  the  original 
bears  heating  to  about  230°  F.,  a  copy  in  one  of  the  readily 
fusible  alloys  given  later  on  may  be  made.  If  it  will  stand 
heat  and  pressure,  it  is  best  to  mould  in  gutta-percha,  but  if 
no  pressure  and  only  slight  heat  can  be  used,  recourse  may  be 
had  to  oil  gutta-percha.  If  neither  heat  nor  pressure  can  be 
applied,  the  moulds  will  have  to  be  executed  in  plaster  of 
Paris  or  in  glue.  The  manner  of  moulding  and  the  material 
to  be  chosen  furthermore  depend  on  whether  surfaces  in  high 
relief  or  round  plastic  bodies  are  to  be  copied,  whether  pro- 
jecting portions  are  undercut,  and  whether  the  mould  can  be 
directly  detached,  or,  if  this  is  not  the  case,  whether  the  orig- 
inal has  to  be  dissected  and  moulded  in  separate  parts. 


GALVANOPLASTY  (REPRODUCTION).  635 

Regarding  the  practice  of  moulding,  the  reader  is  referred 
to  special  works  on  that  subject.  Only  the  main  points  for 
the  most  frequently  occurring  reproductions  will  here  be  given. 

Surfaces  in  relief  and  not  undercut  are  readily  moulded  in  an 
elastic  mass,  such  as  gutta-percha  or  wax  ;  however,  undercut 
reliefs,  and  especially  round  plastic  objects,  mostly  require  a 
plaster-of-Paris  mould  and  are  generally  dissected.  The  dis- 
section, of  course,  is  not  carried  further  than  absolutely  neces- 
sary, because  the  separate  parts  must  be  united  by  a  soldering 
seam,  which  requires  careful  work,  and  the  seam  itself  must  be 
worked  over  and  made  invisible.  Hence  the  section  should  as 
much  as  possible  be  made  through  smooth  surfaces,  edges, 
etc.,  where  the  subsequent  union  by  a  soldering  seam  will 
prove  least  troublesome ;  cutting  through  ornaments  or 
through  portions,  the  accurate  reproduction  of  which  is  of  the 
utmost  importance,  should  be  avoided.  Heads  and  busts  are 
always  executed  in  a  core  mould  and  in  portions,  unless  the 
entire  figure  is  to  be  deposited  in  one  piece  in  a  closed  mould. 
The  section  is  made  either  through  the  center  line  of  the  head 
through  the  nose,  which,  however,  makes  the  subsequent  union 
very  troublesome,  if  the  copy  is  to  be  an  exact  reproduction  of 
the  original,  or  the  mould  is  divided  from  ear  to  ear,  which 
has  the  disadvantage  that  the  deepest  part  of  the  mould  cor- 
responding to  the  nose  receives  the  thinnest  deposit.  It  has, 
therefore,  been  proposed  to  make  two  cuts  so  that  three  por- 
tions are  formed  ;  one  cut  from  one  ear  at  the  commencement 
of  the  growth  of  hair  to  the  other  ear  ;  and  the  second  cut  from 
one  ear  in  a  downward  direction  below  the  lower  jaw  in  the 
joint  of  the  head  and  neck,  through  this  joint  below  the  chin, 
and  then  upwards  to  the  other  ear,  and  in  front  of  it  to  where 
the  hair  begins.  In  bearded  male  heads  the  cut  follows  the 
contour  of  the  beard  and  not  the  joint  on  the  neck  behind  the 
beard. 

Moulding  with  oil  gutta-percha. — Oil  gutta-percha  has  the 
advantage  of  allowing  moulding  without  any  pressure  of  the 
largest  shield-shaped  or  semi-circular  objects  with  all  the 


636  ELECTRO- DEPOSITION    OF    METALS. 

under-culs,  which  otherwise  can  only  be  accomplished  with 
glue.  The  mould  can  be  readily  detached  from  the  original 
as  well  as  from  the  deposit,  which  is  of  great  advantage.  But 
on  the  other  hand,  oil  gutta-percha  deteriorates  by  frequent 
use,  and  sticks  to  the  mould  when  worked  too  hot,  the  result 
being  that  it  is  difficult  to  detach  from  the  original,  and, 
besides,  air  bubbles  are  formed.  However,  the  heat  must 
neither  be  too  slight,  otherwise  the  sharpness  of  the  impres- 
sion would  suffer. 

.  Oil  gutta-percha  is  prepared  by  heating  on  the  water-bath 
100  parts  of  gutta-percha,  10  parts  of  olive  oil  and  2  parts  of 
stearine. 

The  original,  preferably  of  copper,  should  be  slightly  oiled. 
It  is  laid  upon  an  iron  plate  and  the  latter  heated  by  a  flame 
until  the  origjnal  can  be  just  for  a  moment  retained  in  the 
hand.  The  oil  gutta-percha,  previously  heated  on  a  sand-bath 
and  thoroughly  stirred,  is  then  brought  in  a  slow  stream  upon 
the  original.  After  allowing  the  oil  gutta-percha  to  congeal 
superficially,  the  original,  together  with  the  heating  plate,  is 
brought  into  cold  water,  where  complete  congealing  soon  takes 
place. 

For  moulding  in  the  press  or  by  hand  with  oil  gutta- 
percha,  the  heated  mass  is  poured  into  cold  water  and  then 
kneaded  to  the  consistency  of  stiff  dough. 

Moulding  with  gutta-percha. — To  mould  round  articles  in 
gutta-percha,  the  softened  gutta-percha  is  kneaded  with  wet 
hands  upon  the  oiled  original,  or,  in  order  to  avoid  some  por- 
tions receiving  a  stronger  pressure  than  others,  and  to  insure 
a  layer  of  gutta-perch  of  uniform  thickness  upon  all  parts, 
moulding  may  also  be  executed  in  a  ring  or  frame  of  iron  or 
zinc  under  a  press.  For  the  rest,  all  that  has  been  previously 
said  in  regard  to  moulding  in  gutta-percha  is  also  applicable. 

Metallic  moulds. — The  following  metallic  alloys  have  been 
proposed  for  the  preparation  of  moulds  : 

I.  Lead  2  parts,  tin  3,  bismuth  5  ;  fusible  at  212°  F. 
II.  Lead  5,  tin  3,  bismuth  8  ;  fusible  at  183°  F. 


GALVANOPLASTY    (REPRODUCTION).  637 

III.  Lead  2,  tin  2,  bismuth  5,  mercury  1 ;  fusible  at  158°  F. 

IV.  Lead  5,  tin  3,  bismuth  5,  mercury  2;  fusible  at  127.5°  F. 
The  advantage  of  metallic  moulds  consists  in  the  metal 

being  a  good  conductor  of  electricity,  in  consequence  of  which 
heavy  deposits  of  greater  uniformity  can  be  produced  than 
with  non-metallic  moulds  which  have  been  made  conductive 
by  black  lead.  Nevertheless,  they  are  but  seldom  employed, 
on  account  of  the  crystalline  structure  of  the  alloys  and  the 
difficulty  of  avoiding  the  presence  of  air  bubbles.  Bottger 
claims  that  a  mixture  of  lead  8  parts,  tin  3,  and  bismuth  8, 
which  is  fusible  at  227°  F.,  shows  a  less  coarse-grained 
structure. 

Fusible  alloys  containing  mercury  should  not  be  used  for 
taking  casts  of  metallic  objects — iron  excepted — as  these  will 
amalgamate  with  the  mercury  and  be  injured.  Moreover, 
copper  deposits  produced  upon  such  alloys  are  very  brittle,  this 
being  due  to  the  combination  of  the  mercury  with  the  de- 
posited copper. 

For  moulding  with  metallic  alloys,  place  the  oiled  object  at 
the  bottom  of  a  shallow  vessel  and  pour  the  liquid  metal  upon 
it ;  or  pour  the  liquid  metal  into  a  box,  remove  the  la}7er  of 
oxide  with  a  piece- of  thick  paper,  and  when  the  metal  is  just 
beginning  to  congeal  firmly  press  the  object  upon  it. 

Plaster- of -Paris  moulds  are  used  for  making  casts  of  portions 
from  originals  which  are  so  strongly  undercut  that  a  mould 
consisting  of  one  piece  could  not  be  well  detached  from  them. 
For  taking  casts  from  metallic  coins  and  medals,  or  from  small 
plaster  reliefs,  it  is  a  very  convenient  material.  The  mode  of 
procedure  is  as  follows :  After  the  original  model,  say  a 
medal,  has  been  thoroughly  soaped  or  black-leaded,  wrap 
round  the  rim  a  piece  of  sufficiently  stout  paper  or  thin  lead 
foil,  and  bind  it  in  such  a  manner  by  means  of  sealing-wax 
that  the  face  of  the  medal  is  at  the  bottom  of  the  receptacle 
thus  formed.  Then  place  the  whole  to  a  certain  depth  in  a 
layer  of  fine  sand,  which  prevents  the  escape  of  the  semi-fluid 
plaster  of  Paris  between  the  rim  of  the  medal  and  the  paper. 


638  ELECTRO-DEPOSITION    OF    METALS. 

Now  mix  plaster  of  Paris  with  water  to  a  thin  paste,  take  up 
a  small  quantity  of  this  paste  with  a  pencil  or  brush  and 
spread  it  in  a  thin  film  carefully  and  smoothly  over  the  face 
of  the  medal,  then  pour  on  the  remainder  of  the  paste  up  to  a 
proper  height,  and  allow  it  to  set.  After  a  few  minutes  the 
plaster  heats  and  solidifies.  Then  remove  the  surrounding 
paper,  scrape  off  with  a  knife  what  has  run  between  the  paper 
and  the  rim  of  the  medal,  and  carefully  separate  the  plaster 
cast  from  the  model.  If,  instead  of  applying  the  first  layer 
with  a  brush,  the  whole  of  the  plaster  were  run  at  once  into 
the  receptacle,  there  would  be  great  risk  of  imprisoning  air 
bubbles  between  the  model  and  the  mould,  which  would  con- 
sequently be  worthless.  The  mould  is  finally  made  impervious 
and  conductive  according  to  one  of  the  methods  to  be  de- 
scribed later  on. 

The  moulding  in  plaster  of  Paris  in  portions,  when  casts 
from  large  plastic  objects  with  undercut  surfaces  and  reliefs 
are  to  be  taken,  is  troublesome  work,  because  each  separate 
mould  must  not  only  be  so  that  it  can  be  readily  separated 
without  injury  to  the  original,  but  must  also  fit  closely  to  its 
neighbors.  Hence  thought  and  judgment  are  required  to  see 
of  which  parts  separate  moulds  are  to  made,  or,  in  other 
words,  in  how  many  parts  the  mould  is  to  be  made.  After 
determining  on  the  plan  of  the  work,  the  mode  of  procedure 
is  as  follows  :  Oil  a  portion  of  the  object,  if  it  consists  of  metal, 
or  soap  it,  if  of  plaster-of-Paris,  marble,  wood,  etc.,  and  apply 
by  means  of  a  brush  a  thinly-fluid  paste  of  plaster-of-Paris, 
taking  care  that  no  air  bubbles  are  formed  by  the  strokes  of 
the  brush.  When  this  thin  coat  is  hard,  continue  the  appli- 
cation of  plaster-of-Paris  with  a  horn  spatula  until  the  coat 
has  acquired  a  thickness  of  f  to  1  inch,  and  allow  it  to  harden. 
Then  separate  the  mould,  and  after  cutting  or  sawing  the 
edges  square  and  smooth,  replace  it  upon  the  portion  of  the 
original  model  corresponding  to  it.  Now  oil  or  soap  the 
neighboring  portions  of  the  model,  and  at  the  same  time  the 
smooth  edges  of  the  first  mould  which  come  in  contact  with 


GALVANOPLASTY    (REPRODUCTION).  639 

the  mould  now  to  be  made,  and  then  proceed  to  make  the 
second  mould  in  precisely  the  same  manner  as  the  first. 
When  the  second  mould  is  hard,  trim  the  edges  and  replace 
it  upon  the  model ;  the  same  process  being  continued  until  the 
entire  original  model  is  reproduced  in  moulds  fitting  well  to- 
gether. To  prevent  the  finished  moulds  from  falling  off,  and 
to  retain  them  in  a  firm  position  upon  the  original  model, 
they  are  tied  with  lead  wire  or  secured  with  catches  of  brass 
wire  or  sheet.  When  the  moulds  of  the  larger  portion  of  the 
model,  for  instance,  one-half  of  a  statue,  are  finished,  the  so- 
called  case  or  shell  is  made,  i.  e.,  the  backs  of  all  the  moulds 
are  coated  with  a  layer  of  plaster-of-Paris  which  holds  them 
together.  This  case  is  best  made  not  too  thin  in  order  to  at- 
tain a  better  resisting,  power. 

The  entire  model  having  been  cast  in  the  manner  above 
described,  and  the  moulds  provided  with  the  case,  the  whole 
is  completely  dried  in  an  oven. 

Rendering  plaster- of -Paris  moulds  impervious. — The  next 
operation  is  to  make  the  plaster-of-Paris  impervious  to  fluids, 
as  otherwise  by  the  moulds  absorbing  the  acid  copper  bath, 
copper  would  be  deposited  in  the  pores  of  the  plaster  and  the 
moulds  be  spoiled,  while  the  copy  would  turn  out  rough  in- 
stead of  having  the  smooth  exterior  of  the  model.  To  render 
plaster-of-Paris  and  other  porous  substances  impervious,  they 
are  saturated  with  wax  or  stearine,  or  covered  with  a  coat  of 
varnish,  the  latter  process  being  generally  employed  for  large 
moulds.  Apply  a  coat  of  thick  linseed-oil  varnish  to  the  face 
of  the  mould,  and,  after  drying,  repeat  the  process  until  the 
mould  is  considered  to  be  sufficiently  impervious. 

Rendering  the  mould  impervious  with  wax  or  stearine  is  a 
better  and  more  complete  method.  For  this  purpose  place 
the  heated  mould  in  a  vat  filled  with  melted  wax  or  stearine, 
so  that  the  face  does  not  come  in  contact  with  the  wax  but 
absorbs  it  by  capillarity  from  the  bath.  However,  as  this 
cannot  be  done  in  every  case,  the  mould,  if  necessary,  may  be 
entirely  submerged  in  the  melted  wax  until  no  more  air- 


640  ELECTRO-DEPOSITION    OF    METALS. 

bubbles  escape.  It  is  then  taken  from  the  bath  and  laid,  face 
up,  in  a  drying  oven,  whereby  the  wax  in  melting  oozes  down 
in  consequence  of  its  gravity,  the  face  of  the  mould  being  thus 
freed  from  an  excess  of  wax. 

To  prevent  the  removal  of  too  much  wax  from  the  face,  the 
mould  is  cooled  off  with  cold  water  the  moment  the  excess  of 
wax  is  noticed  to  have  penetrated  from  the  face  into  the  in- 
terior. After  drying  the  mould,  the  face  is  coated  with  gutta- 
percha  lacquer,  in  order  to  make  the  high  reliefs,  which  may 
have  been  too  much  freed  from  wax,  impervious.  Gutta- 
percha  lacquer  is  prepared  as  follows  : 

Bring  into  a  wide-mouthed  glass  bottle  provided  with  a 
glass-stopper,  gutta-percha  cut  up  in  small  pieces,  and  fill  the 
bottle  with  a  mixture  of  equal  parts  by  volume  of  ether  and 
benzol.  The  bottle  is  allowed  to  stand  for  several  weeks  in  a 
moderately  warm  room,  the  contents  being  frequently  shaken. 
In  this  time  as  much  gutta-percha  as  the  solvent  can  absorb 
will  be  dissolved. 

For  rendering  impervious  porous,  non-metallic  moulds  upon 
which  copper  is  later  on  to  be  deposited,  Greif  has  patented 
the  following  process :  The  impregnating  agent  consists  of 
about  70  parts  coal-tar  pitch,  20  parts  retene  (methylpropyl 
phenanthrene),  and  10  parts  naphthalene.  The  mixture  of 
the  ingredients  having  been  melted  by  steam,  the  body  to  be 
impregnated  is  immersed  in  the  liquid  mass,  and  allowed  to 
remain  in  it  a  short  time  to  become  throughout  impregnated. 
An  excess  of  the  impregnating  agent  is  readily  removed  by 
allowing  it  to  drain  off. 

Metallizing  or  rendering  the  moulds  conductive. — Metallization 
by  the  dry  way.  The  moulds  thus  varnished  or  impregnated 
with  wax  are  next  rendered  conductive  with  black  lead,  the 
operation  being  the  same  as  that  for  moulds  for  the  graphic  arts. 

In  some  cases  metallization  by  metallic  powders  is,  however, 
to  be  preferred  to  black-leading  or  metallizing  by  the  wet  way. 
Metallic  or  bronze  powders  are  metals  in  an  exceedingly  fine 
state  of  division,  of  which,  for  galvanoplastic  purposes,  pure 


GALVANOPLASTY  (REPRODUCTION).  641 

copper  and  brass  powders  only  are  of  interest.  Since  such 
metallic  powders  adhere  badly  to  waxed  surfaces,  the  mould 
must  be  provided  with  a  quick-drying  coat  of  lacquer,  upon 
which,  before  it  is  completely  dry,  the  powder  is  scattered  or 
sifted.  When  the  lacquer  is  hard  a  smooth  surface  is  pro- 
duced by  going  over  the  mould  with  a  soft  brush  dipped  in 
the  metallic  powder,  an  excess  being  removed  by  a  thin  jet  of 
water. 

For  many  undercut  or  very  deep  portions  which  cannot  te 
thoroughly  manipulated  with  the  brush,  metallization  with 
black-lead  proves  insufficient,  and  recourse  will  have  to  be 
had  to 

Metallization  by  the  wet  way. — This  method  consists  in  the 
deposition  of  certain  metallic  salts  upon  the  moulds  and  their 
reduction  to  metal  or  conversion  to  conductive  sulphur  combi- 
nations. The  process  in  general  use  is  as  follows  :  Apply  with 
a  brush  upon  the  mould  a  not  too  concentrated  solution  of 
silver  nitrate  in  a  mixture  of  equal  parts  of  distilled  water  and 
90  per  cent,  alcohol.  When  the  coat  is  dry  expose  it  in  a 
closed  box  to  an  atmosphere  of  sulphuretted  hydrogen.  The 
latter  converts  the  silver  nitrate  into  silver  sulphide,  which  is 
a  good  conductor  of  the  current.  For  the  production  of  the 
sulphuretted  hydrogen,  place  in*  the  box,  which  contains  the 
mould  to  be  metallized,  a  porcelain  plate  or  dish  filled  with 
dilute  sulphuric  acid  (1  acid  to  8  water),  and  add  five  or  six 
pieces  of  iron  pyrites  the  size  of  a  hazelnut.  The  development 
of  the  gas  begins  immediately,  and  the  box  should  be  closed 
with  a  well-fitting  cover  to  prevent  inhaling  the  poisonous  gas ; 
if  possible  the  work  should  be  done  in  the  open  air  or  under 
a  well-drawing  chimney.  The  formation  of  the  layer  of  silver 
sulphide  requires  but  a  few  minutes,  and  if  not  many  moulds 
have  to  be  successively  treated,  the  acid  is  poured  off  from  the 
iron  pyrites  and  clean  water  poured  upon  the  latter  so  as  not 
to  cause  useless  development  of  gas. 

It  has  also  been  recommended  to  decompose  the  silver  salt  by 
vapors  of  phosphorus  and  to  convert  it  into  silver  phosphide, 
41 


642  ELECTRO-DEPOSITION    OF    METALS. 

a  solution  of  phosphorus  in  carbon  disulphide  being  used  for 
the  purpose.  The  layer  of  silver  salt  is  moistened  with  the 
solution  or  exposed  to  its  vapors.  This  method  possesses,  how- 
ever, no  advantage  over  the  preceding  one,  because,  on  the  one 
hand,  the  phosphorus  solution  takes  fire  spontaneously,  and, 
on  the  other,  the  odor  of  the  carbon  disulphide  is  still  more 
offensive  than  that  of  sulphuretted  hydrogen. 

A  somewhat  modified  method  is  given  by  Parkes  as  follows : 
Three  solutions,  A,  B,  C,  are  required.  Solution  A  is  prepared 
by  dissolving  0.5  part  of  caoutchouc  cut  up  in  fine  pieces  in  10 
parts  of  carbon  disulphide  and  adding  4  parts  of  melted  wax  ; 
stir  thoroughly,  then  add  a  solution  of  5  parts  of  phosphorus 
in  60  of  carbon  disulphide,  together  with  5  of  oil  of  turpentine 
and  4  of  pulverized  asphalt ;  then  thoroughly  shake  this  mix- 
ture, A.  Solution  B  consists  of  2  parts  by  weight  of  silver 
nitrate  in  600  of  water;  and  solution  C  of  10  parts  of  gold 
chloride  in  600  of  water.  The  mould  to  be  metallized  is  first 
provided  with  wires  and  then  brushed  over  with  or  immersed 
in  solution  A,  and  after  draining  off,  dried.  The  dry  mould  is 
then  poured  over  with  the  silver  solution  (B)  and  suspended 
free  for  a  few  minutes  until  the  surface  shows  a  dark  luster. 
It  is  then  rinsed  in  water  and  treated  in  the  same  manner 
with  the  chloride  of  gold  solution  (C),  whereby  it  acquires  a 
yellowish  tone,  when,  after  drying,  it  is  sufficiently  prepared 
for  the  reception  of  the  deposit.  Care  must  be  taken  in  pre- 
paring solution  A,  carbon  disulphide  which  contains  phos- 
phorus readily  taking  fire. 

However,  in  some  cases,  either  one  of  the  above-mentioned 
methods  may  leave  the  operator  in  the  lurch.  On  the  one 
hand,  a  small  .accumulation  of  silver  salt  solution  in  the 
deeper  places  cannot  be  well  prevented,  a  slightly  crystalline 
layer  of  salt  being  consequently  formed  and,  on  the  other,  it 
may  happen  that  the  layer  of  silver  sulphide  becomes  without 
discernible  reason  detached  from  the  mould  in  the  copper 
bath,  thus  necessitating  a  repetition  of  the  process. 

In  manv  cases  the  following  method  has  been  successfully 


GALVANOPLASTY  (REPRODUCTION).  643 

used  :  Dilute  iodized  collodion  solution,  such  as  is  used  for 
photographic  purposes,  with  an  equal  volume  of  ether-alcohol, 
and  pour  this  solution  quickly  and  without  intermission  over 
the  mould,  the  latter  being  inclined  so  that  all  portions  of  it 
come  in  contact  with  the  collodion  solution,  when  the  mould  is 
turned  face  down  to  allow  an  excess  to  run  off.  By  manipu- 
lating with  sufficient  rapidity  a  film  of  collodion  solution  re- 
mains upon  the  mould.  This  film,  at  the  moment  of  congeal- 
ing, is  exposed  for  2  to  3  minutes  to  the  action  of  a  weak 
solution  of  silver  nitrate  in  water,  the  operation  being  best 
effected  in  a  darkened  room.  The  collodion  containing  potas- 
sium iodide  forms  with  the  silver  bath,  silver  iodide,  the  pre- 
viously clear  collodion  layer  becoming  yellowish.  In  this 
state  the  mould  is  taken  from  the  silver  bath,  washed  with  a 
weak  jet  of  water  to  remove  an  excess  of  silver  solution,  and 
then  for  a  few  minutes  exposed  to  the  sun.  By  this  means  a 
reduction  of  the  silver  salt  takes  place,  which  is  rendered  still 
more  intense  by  laying  the  mould  in  a  solution  of  copperas  in 
water,  alcohol  and  glacial  acetic  acid,  in  the  proportion  of 
1.76  ozs.  copperas,  1  oz.  glacial  acetic  acid,  0.7  oz.  alcohol  per 
quart  of  water.  The  mould  is  then  rinsed  in  water  and 
immediately  brought  into  the  copper  bath,  the  conduction  of 
the  current  to  the  layer  of  silver  having  been  first  effected  by 
means  of  a  few  feelers. 

In  applying  this  method  it  must  be  borne  in  mind  that  the 
collodion  layer  will  not  bear  rough  handling,  and  injury  of  it, 
by  touching  it  with  the  hands  or  a  strong  jet  of  water,  or  by 
careless  application  of  the  conducting  wires  (feelers),  must  be 
avoided.  When  operating  with  the  care  required,  the  results 
are  very  satisfactory  and  sure. 

In  place  of  iodized  collodion,  a  mixture  of  equal  parts  of 
white  of  egg  and  saturated  common  salt  solution  may  be  used, 
the  process  for  the  rest  being  the  same  as  above  described. 

Lenoir's  process — Galvanoplastic  method  for  originals  in  high 
relief. — Lenoir's  method  for  reproducing  statues  in  a  manner 
approaches  in  principle  to  that  of  the  foundry.  He  begins  by 


644  .      ELECTRO-DEPOSITION    OF    METALS. 

making  with  gutta-percha  a  mould  in  several  pieces,  which 
are  united  together  so  as  to  form  a  perfect  hollow  mould  of  the 
original.  This  having  been  done,  cover  all  the  parts  carefully 
with  black-lead.  Make  a  skeleton  with  platinum  wire,  follow- 
ing the  general  outline  of  the  model,  but  smaller  than  the 
mould,  since  it  must  be  suspended  in  it  without  any  point  of 
contact.  If  the  skeleton  thus  prepared  is  enclosed  in  the 
metallized  gutta-percha  mould,  and  the  whole  immersed  in  the 
galvanoplastic  bath,  it  will  be  sufficient  to  connect  the  inner 
surface  of  the  mould  with  the  negative  pole  of  the  battery,  and 
the  skeleton  of  platinum  wires  (which  should  have  no  points 
of  contact  with  the  metallized  surfaces  of  the  mould)  with  the 
positive  pole,  in  order  to  decompose  the  solution  of  sulphate 
of  copper  which  fills  the  mould.  When  the  metallic  deposit 
has  reached  the  proper  thickness  the  gutta-percha  mould  is 
removed  by  any  convenient  process,  and  a  faithful  copy  of  the 
original  will  be  produced.  Lead  wires  may  be  substituted  for 
the  expensive  platinum  wires.  This  method  requires  a  knowl- 
edge of  the  moulder's  art,  so  that  good  results  can  only  be 
obtained  by  an  experienced  hand. 

Gelatine  moulds. — Under  certain  conditions  the  elasticity  of 
gelatine  allows  of  the  possibility  of  its  removal  from  undercut 
or  highly-wrought  portions  of  the  model,  when  it  reassumes 
the  shape  and  position  it  had  before  removal  therefrom.  But 
gelatine  requires  that  the  deposit  shall  be  made  rapidly,  other- 
wise it  will  swell  and  be  partially  dissolved  by  too  long  an 
immersion  in  the  copper  bath. 

To  make  .a  good  gelatine  mould,  proceed  as  follows:  Allow 
white  gelatine  (cabinet-maker's  glue)  to  swell  for  about  24 
hours  in  cold  water,  then  drain  off  the  water,  and  heat  the 
swollen  mass  in  a  water-bath  until  completely  dissolved. 
Compound  the  glue  solution  with  pure  glycerine  in  the  pro- 
portion of  5  to  10  cubic  centimeters  (0.24  to  0.3  cubic  inch) 
of  glycerine  to  30  grammes  (1.05  ozs.)  of  gelatine,  which 
prevents  the  gelatine  from  shrinking  in  cooling.  When  some- 
what cooled  off',  apply  the  gelatine  to  the  oiled  original,  which 


GALVANOPLASTY  (REPRODUCTION).  645 

must  be  surrounded  with  a  rim  of  plaster  of  Paris  or  wax,  to 
prevent  the  gelatine  from  running  off;  when  cold,  lift  the 
gelatine  mould  from  the  model.  Before  metallizing  and  sus- 
pending in  the  copper  bath,  the  mould  has  to  be  prepared  to 
resist  the  action  of  the  latter,  as  otherwise  it  would  at  once 
swell  and  be  partially  dissolved  before  being  covered  with  the 
deposit.  This  is  effected  by  placing  the  mould  in  a  highly 
concentrated  solution  of  tannin,  which  possesses  the  property 
of  making  gelatine  insoluble. 

Brandley  gives  the  following  directions  for  preparing  gela- 
tine solution  with  an  addition  of  tannin,  which  renders  the 
moulds  impervious  to  water:  Dissolve  20  parts  of  the  best 
gelatine  in  100  of  hot  water,  add  J  part  of  tannic  acid  and  the 
same  quantity  of  rock  candy,  then  mix  the  whole  thoroughly, 
and  pour  it  upon  the  model. 

The  same  object  is  attained  by  the  use  of  potassium  dichro- 
mate  solution  in  place  of  tannin  solution.  In  this  case,  the 
potassium  dichromate  solution  must  be  allowed  to  act  in  a 
dark  room,  the  mould  being  then  for  some  time  exposed  to  the 
action  of  the  sun.  The  chrome  gelatine  layer  formed  upon  the 
surface  does  not  swell  up,  and  is  insoluble,  at  least  for  the  time 
required  to  cover  the  mould  with  copper.  Rendering  glue 
moulds  conductive  by  means  of  black-lead  is,  as  a  rule,  im- 
practicable, and  metallization  has  to  be  accomplished  by  the 
wet  way  in  order  to  effect  a  rapid  formation  of  the  deposit. 
Moulds  rendered  conductive  by  black-lead  should  be  rapidly 
covered  with  copper  while  the  bath  is  being  agitated,  because 
a  bath  in  which  a  considerable  quantity  of  gelatine  has  been 
dissolved,  yields  brittle  copper,  while  by  a  very  small  quantity 
of  it,  the  density  of  the  deposit  is  increased. 

Special  Applications  of  Galvanoplasty. 

Nature  printing,  so  named  by  Mr.  v.  Auer,  Director  of  the 
Imperial  Printing  Office  at  Vienna,  has  for  its  object  the  gal- 
vanoplastic  reproduction  of  leaves  and  other  similar  bodies. 
The  leaf  is  placed  between  two  plates,  one  of  polished  steel, 


646  ELECTRO-DEPOSITION    OP    METALS. 

the  other  of  soft  lead,  and  is  then  passed  between  rollers, 
which  exert  a  considerable  pressure.  The  leaf  thus  imparts 
an  exact  impression  of  itself  and  of  all  its  veins  and  markings 
to  the  lead,  and  this  impression  may  be  electrotyped,  and  the 
copper  plate  produced  used  for  printing  in  the  ordinary  way. 
Instead  of  taking  the  impression  in  lead,  it  is  advisable  to  use 
gutta-percha  or  wax  for  delicate  objects,  which  should  pre- 
viously be  black-leaded  or  oiled.  In  the  same  manner  gal- 
vanoplastic  copies  of  laces,  etc.,  may  be  obtained. 

Elmore  produces  copper  tubes  by  galvanoplastic  deposition 
by  allowing  the  metallic  core-bar  to  revolve  slowly  between 
the  anodes,  while  a  polishing  steel  is  by  means  of  a  mechan- 
ical contrivance  carried  with  strong  pressure  over  the  deposit, 
whereby  the  latter  is  made  dense  and  any  roughness  removed. 

It  would  seem  that  the  process  for  the  production  of  copper 
tubes,  profiled  hollow  copper  bodies,  etc.,  patented  by  Ignaz 
Klein,  is  better  than  Elmore's  method.  The  black-leaded  or 
metallic  core-bars  are  allowed  to  roll  to  and  fro  upon  smooth 
or  profiled  plates,  the  so-called  milling  plates,  or  the  core-bars 
are  concentrically  arranged  around  a  cylindrical  anode  and 
allowed  with  pressure  to  roll  on  an  exterior  round  milling  sur- 
face. According  to  this  method,  the  space  in  the  baths  can 
be  better  utilized  than  in  the  Elmore  process,  and  the  deposit 
shows  excellent  properties  as  regards  uniform  density  and 
power  of  resistance. 

According  to  Dieffenbach  and  Limpricht's  method  (German 
patent  125404)  tubes  and  hollow  bodies  of  copper  of  great 
toughness  and  strength  are  obtained  by  allowing  the  metal 
cores,  or  other  cores  rendered  conductive  in  a  suitable  manner, 
to  revolve  in  an  acid  bath  to  which  fine  sand  or,  better,  in- 
fusorial earth  has  been  added.  The  infusorial  earth  exerts  a 
scouring  effect  and  removes  any  hydrogen  bubbles  which  may 
have  been  separated.  Experiments  made  with  this  process 
yielded  copper  tubes  which  on  being  tested  showed  excellent 
values  as  regards  strength. 

Corvin's  niello. — Corvin  has  invented  a  process  of  producing 


GALVANOPLASTY    (REPRODUCTION).  647 

inlaid  work  by  galvanoplasty.  The  process  is  as  follows :  A 
matrice  of  metal  whose  surface  is  finely  polished  is  first  made. 
This  matrice  may  be  used  for  the  production  of  numerous 
duplicates  of  the  same  kind  of  object.  The  incrustations 
(mother-of-pearl,  glass,  ivory,  amber,  etc.)  are  then  shaped  by 
means  of  a  saw,  files  and  other  tools  to  the  form  corresponding 
to  that  which  they  are  to  occupy  in  the  design.  The  side  of 
the  incrustation  which  is  laid  upon  the  matrice  is,  as  a  rule, 
smooth.  The  shaped  incrustations,  smooth  side  down,  are 
pasted  on  to  the  parts  of  the  model  they  are  to  occupy  in  the 
design.  The  latter  being  thus  produced,  the  backs  of  the 
non-metallic  laminae  are  metallized,  and  the  portions  of  the 
metallic  plate  left  free  are  slightly  oiled.  By  now  placing  the 
matrice  thus  prepared  in  the  galvanoplastic  bath,  the  copper 
is  deposited,  not  only  upon  the  metallic  matrice,  but  also  upon 
the  back  of  the  inlaid  pieces,  the  latter  being  firmly  inclosed 
by  the  deposited  metal.  When  the  deposited  metal  has  ac- 
quired the  desired  thickness,  it  is  detached  from  the  matrice, 
and  incrustations  with  the  right  side  polished  are  thus  ob- 
tained. The  laminae  are  more  accurately  and  evenly  laid  in 
than  would  be  possible  by  the  most  skilled  hand-work. 

Plates  for  the  production  of  imitations  of  leather.  The  demand 
for  alligator  and  similar  leathers  is  at  the  present  time  greater 
than  the  supply,  and,  therefore,  imitations  are  made  by  press- 
ing ox-leather,  the  plate  being  prepared  by  galvanoplasty,  as 
follows  :  A  large  piece  of  the  natural  skin  or  leather  is  made 
impervious  to  the  bath  by  repeated  coatings  with  lacquer,  and, 
when  completely  dr}r,  secured  with  asphalt  lacquer  to  a  cop- 
per or  brass  plate.  The  leather  is  then  black-leaded,  and,  after 
being  made  conductive  by  copper  wire  or  small  lead  plates, 
brought  into  the  copper  bath.  When  the  copper  deposit  has 
acquired  the  desired  thickness,  the  plate  is  further  strength- 
ened by  backing  with  stereotype  metal. 

Incrusting  galvanoplasty. — This  term  may  be  applied  to  the 
process  by  which  a  thick  coat  of  copper,  or  of  another  metal, 
is  deposited  upon  an  article.  This  deposit,  however,  is  not 


G48  ELECTRO-DEPOSITION    OF    METALS. 

detached  from  the  original,  as  in  reproduction-gal vanoplasty, 
but  remains  upon  it,  the  object  being,  as  a  rule,  to  embellish 
the  article  or  to  give  non-metallic  articles  the  appearance  of 
metallic  ones. 

Non-metallic  objects  to  be  coated  have  also  to  be  rendered 
impervious  to  the  electrolyte,  great  care  being  required  in  this 
respect,  since  in  case  the  acid  copper  bath  penetrates  into  the 
article  to  be  coated,  the  deposit  would  later  on  effloresce  and 
peel  off. 

The  objects  may  be  rendered  impervious  by  one  of  the 
methods  mentioned  above,  it  being  best,  however,  first  to  heat 
them,  as  for  instance,  terra-cotta  busts,  and  then  place  them  in 
melted  wax,  or  mixtures  of  wax  and  paraffine.  By  heating 
the  greater  portion  of  the  air  is  expelled  from  the  pores,  the 
wax  thus  penetrating  better  and  closing  the  pores.  An  excess 
of  wax  is  removed  by  draining  off  in  a  warm  room  (air-bath), 
and  when  cold  the  objects  are  coated  with  gutta-percha  lacquer 
and  metallized  with  black-lead. 

However,  it  will  frequently  be  impracticable  to  reach  every 
portion  with  the  black-lead  brush,  and  in  this  case  it  is  recom- 
mended to  effect  metallization  by  the  wet  way,  as  follows : 

Coat  the  articles,  previously  rendered  impervious,  with  a 
thickly-fluid  solution  of  shellac  in  alcohol,  and  allow  them  to 
become  thoroughly  dry.  Then  immerse  them  for  one  minute 
in  saturated  silver-nitrate  solution  in  4  parts  of  water  and  6 
parts  of  alcohol,  and  allow  them  to  drain  off.  Bring  the  arti- 
cles, while  still  moist,  into  a  vessel  which  can  be  closed  air- 
tight, and  introduce  sulphuretted  hydrogen.  A  thin  layer  of 
silver  sulphide  will  in  a  few  minutes  be  formed,  when  the  arti- 
cles are  taken  from  the  vessel  and  allowed  to  dry,  the  same 
manipulation  being  once  or  twice  repeated.  By  operating  in 
this  manner,  non-success  is  next  to  impossible,  because  when 
the  object  is  immersed  in  the  alcoholic  silver-nitrate  solution, 
the  coat  of  lacquer  is  superficially  softened  and  absorbs  silver 
nitrate,  which  after  its  conversion  into  silver  sulphide  adheres 
very  firmly  after  drying,  so  that  the  layer  of  it  becomes  very 


GALVANOPLASTY    (REPRODUCTION).  649 

seldom  detached  in  the  bath.  Should  this  nevertheless  hap- 
pen, it  is  generally  caused  by  the  objects  not  having  been 
thoroughly  dried  between  the  separate  operations. 

Large  objects  which  cannot  be  immersed  will  have  to  be 
carefully  brushed  over  with  the  solutions,  or  the  latter  be 
poured  over  them.  According  to  the  nature  of  the  objects  to 
be  coated,  the  process  may  have  to  be  somewhat  modified,  or 
one  of  the  methods  already  described  will  have  to  be  employed. 
This  will  soon  be  learned  by  experience. 

Copper  bath  and  current  conditions. — Deposits  for  incrusting 
galvanoplasty  should  be  effected  with  very  slight  current- 
densities  in  order  to  avoid  roughness  and  a  coarsely  crystal- 
line structure  of  the  deposit.  For  many  delicate  objects  to  be 
coated  with  copper,  the  use  of  the  cell-apparatus  is  therefore 
advisable. 

Neubeck  has  investigated  the  work  in  the  cell-apparatus 
and  its  application  to  encrusting  galvanoplasty,  and  has  found 
a  copper  bath  which  contains  in  100  quarts,  44  Ibs.  of  crys- 
tallized blue  vitriol  and  13.2  Ibs.  of  sulphuric  acid  of  66°  Be., 
to  be  especially  valuable  for  the  purpose. 

In  place  of  zinc,  he  used  iron  plates  or  iron  tubes,  and  as 
solution,  one  of  sodium  sulphate  with  the  addition  of  a  few 
drops  of  sulphuric  acid.  The  current  generated  by  this  ar- 
rangement produces  a  very  finely  crystalline  deposit  free  from 
roughness  and  efflorescences. 

Additional  manipulation  of  the  deposits. — The  deposits  of 
copper  produced  by  one  or  the  other  method  require,  as  a 
rule,  additional  mechanical  manipulation  to  give  the  outlines 
greater  sharpness,  and  to  the  whole  a  more  pleasing  appear- 
ance. This  is  done  by  chiseling  to  make,  for  instance,  with 
busts,  the  eyes,  nose,  ears,  etc.,  more  prominent.  Scratch- 
brushing,  brushing,  and  polishing  are  applied  if  luster  is  to  be 
imparted  to  the  deposits  as  is  required  for  sufficiently  effective 
nickeling,  gilding,  etc. 

Laces  and  tissues  are,  according  to  Philip,  impregnated  with 
melted  wax,  and  after  removing  an  excess  with  blotting-paper, 


650  ELECTRO-DEPOSITION    OF    METALS. 

they  are  made  conductive  by  black-leading  with  a  brush.  It 
is,  however,  preferable  to  metallize  such  delicate  objects  by 
the  wet  way,  employing  one  of  the  methods  previously  de- 
scribed. 

Grasses,  leaves,  flowers,  etc.,  are  first  dried  and  their  former 
shape  and  elasticity  restored  by  placing  them  for  a  consider- 
able time  in  glycerine.  They  are  then  several  times  immersed 
in  gutta-percha  lacquer,  and  metallized  with  silver  nitrate 
solution  and  sulphuretted  hydrogen,  or  according  to  one  of  the 
oth^r  processes  described. 

Wooden  handles  of  surgical  instruments  are  provided  with  a 
galvanoplastic  deposit  of  copper  to  adapt  them  to  antiseptic 
rules.  The  wood  has  to  be  protected  from  the  bath-fluid  pen- 
etrating into  it,  by  remaining  for  a  considerable  time  in 
melted  wax  or  in  a  solution  of  wax  or  paraffine  in  ether,  as 
otherwise  the  copper-deposit  formed  will  be  broken  by  the 
wood  swelling.  Metallization  is  effected  by  dusting  the  wood 
thus  prepared  with  black  lead  or  bronze  powder,  or  by  the 
wet  way.  The  deposit  is,  as  a  rule,  ground,  polished,  and 
then  nickeled. 

Busts  and  other  objects  of  terra-cotta,  stoneware,  clay,  etc.,  are 
immersed  in  melted  wax  and,  after  removing  an  excess  of 
wax,  coated  with  gutta-percha  lacquer.  If  there  is  no  obstacle 
to  black-leading,  this  method  may  be  used  for  metallization, 
otherwise  recourse  will  have  to  be  had  to  one  of  the  processes 
previously  described. 

When  the  copper  deposit  is  finished  the  objects  should  be 
thoroughly  soaked  in  water,  and  then  for  a  few  hours  placed 
in  a  5  per  cent,  yellow  prussiate  of  potash  solution  for  the 
neutralization  of  any  bath-residue  which  may  still  remain  in 
some  of  the  pores. 

To  bring  out  sharp  outlines,  especially  when  the  deposit  is 
quite  thick,  the  coppered  busts  and  other  objects  are  chiseled, 
scratch-brushed,  and  polished.  They  receive,  as  a  rule,  a 
patina,  according  to  one  of  the  methods  given  in  Chapter 
XIV,  or  are  brassed,  silvered,  or  gilded. 


GALVANOPLASTY  (REPRODUCTION).  651 

The  mercury  vessels  of  thermometers  for  vacuum  and  distilling 
apparatus  are  as  a  protection  given  a  galvanoplastic  deposit  of 
copper.  This  is  effected  in  the  most  simple  manner  by  coat- 
ing the  glass  with  copal  lacquer  and  black-leading  the  layer 
of  lacquer,  or  applying  bronze  powder.  The  glass  may  also 
be  matted  by  the  sand  blast,  or  with  fluoric  acid,  and  directly 
black -leaded,  the  black-lead  adhering  well  to  the  matted  glass 
surface. 

Mirrors  are  coppered  to  protect  the  thin  layer  of  silver  from 
injury.  For  the  success  of  coppering  in  the  acid  copper  bath 
without  danger  of  the  film  of  silver  becoming  detached,  it  is 
necessary  to  use  a  weaker  bath  of  at  the  utmost  8°  to  10°  B6. 
with  1  per  cent,  of  free  sulphuric  acid,  and  to  deposit  with  a 
very  slight  current-density. 

Glass  .and  porcelain  ware,  for  instance,  tumblers,  bowls,  coffee 
and  tea  sets,  when  furnished  with  galvanoplastic  decorations  in 
copper  or  silver,  produce  beautiful  effects.  However,  metalli- 
zation by  one  of  the  processes  thus  far  described  is  not  practi- 
cable, the  high  reliefs  having  to  adhere  firmly  to  the  base,  so 
as  not  to  become  detached  by  cleansing  or  wear. 

Metallization  of  the  portions  to  be  coated  is  effected  by 
painting  the  arabesques,  flowers,  monograms,  etc.,  with  solu- 
tion of  Dutch  gold,  factitious  silver,  or  platinum,  and  after  dry- 
ing, burning-in  in  a  muffle  at  a  dark  red  heat.  A  lustrous 
layer  of  metal  firmly  fused  together  with  the  glaze  is  thus 
obtained  and  is  without  further  preparation  fit  for  coppering 
or  silvering.  Still  greater  solidity  is  attained  by  triturating 
conducting  silver  enamel  with  lavender  oil  upon  a  palette  to 
a  mass  of  the  consistency  of  paint,  applying  the  latter  with  a 
brush  and  burning-in  in  the  muffle.  In  addition  to  pure 
silver,  the  enamel  contains  fluxing  agents  Which  effect  a  firm 
union  of  the  silver  with  the  porcelain  or  glass.  After  burn- 
ing-in, the  decorations  are  gone  over  with  a  fine  copper  brush 
and,  the  conduction  of  the  current  to  the  metallized  portions 
having  been  effected  by  means  of  fine  copper  wires,  the  objects 
are  brought  into  the  galvanoplastic  bath. 


652  ELECTRO-DEPOSITION    OF    METALS. 

Mr.  A.  A.  Le  Fort  *  gives  the  following  process  for  "  silver 
deposit "  on  glass  and  china,  which,  if  followed  according  to 
directions,  will  be  found  satisfactory  in  every  way.  The  color 
will  be  found  a  clear  white  which  is  necessary  on  glass  objects, 
when  the  work  is  fixed  properly  and  being  fused  into  the 
glass  or  china,  will  make  a  firm  body  that  will  hold  the  de- 
posited silver,  so  that  there  will  be  but  a  very  small  loss  in 
the  plating  and  finishing  operations  due  to  the  silver  (failing) 
or  peeling  off,  while  the  loss  is  very  large  when  the  proper 
metallic  paint  or  painting  solutions  are  not  employed.  The 
formula  for  the  metallic  paint,  which  must  be  weighed  ac- 
curately, is  as  follows  : 

"Metallized  silver"  4  ozs.,  boracic  acid  4  dwi,  potassium 
nitrate  4  dwt.,  powdered  flint  4  dwt.,  powdered  glass  4  dwt., 
soda  ash  4  dwt.,  red  lead  4  dwt.,  calcined  borax  8  dwt. 

While  the  named  ingredients  are  used  in  all  paints,  the 
weight  of  each  may  vary  in  different  formulas,  but  the  above 
will  be  found  to  be  one  of  the  best  in  use.  In  order  to  get  the 
silver  ready  for  use  in  the  paint,  it  must  be  treated  as  follows, 
which  is  called  metallizing  :  Either  take  fine  silver  chloride, 
or  else  cut  down  your  own  silver  in  the  usual  way,  namely, 
one  part  water  and  one  part  nitric  acid,  in  a  hot  water  bath, 
precipitate  in  the  usual  way  with  common  salt,  wash  the 
chloride  four  or  five  times,  then  put  the  chloride  in  a  glass  or 
porcelain  bowl,  and  cover  with  a  solution  of  two  parts  sulphuric 
acid  to  seven  parts  of  water.  Then  cut  common  sheet  zinc 
into  sirips  of  about  one-half  inch  in  width  and  four  or  five 
inches  in  length,  and  put  them  in  the  silver  chloride  and  the 
diluted  sulphuric  acid,  stir  occasionally  and  keep  on  adding 
zinc  until  a  gray  or  brownish-colored  precipitate  of  metallic 
silver  is  formed.  *  Wash  thoroughly  until  free  from  acid,  test- 
ing with  blue  litmus  paper  to  make  sure.  After  the  silver  is 
washed,  it  is  necessary  to  dry  it  perfectly,  by  drying  it  in  a 
porcelain  or  other  suitable  vessel  over  a  sand-bath.  Make 

*  Metal  Industry,  February,  1913. 


GALVANOPLASTY    (REPRODUCTION).  653 

sure  that  it  is  perfectly  dry,  so  that  there  will  be  no  error  in 
weighing  when  making  up  the  paint.  If  the  silver  is  damp 
the  weight  will  not  be  correct  to  conform  with  the  other  in- 
gredients in  the  formula. 

After  weighing  all  the  ingredients  named  in  the  formula, 
mix  together,  then  thin  down  with  oil  of  turpentine,  grind  in 
a  paint  mill,  which  is  made  for  that  purpose,  or  grind  by 
hand,  with  a  glass  "  muller  "  on  a  heavy  glass  or  stone,  which 
can  be  procured  from  most  art  or  paint  dealers.  The  grind- 
ing by  hand  is  a  long  and  tedious  operation,  as  it  takes  a  long 
time  to  do  the  work  properly,  for  the  paint  has  to  be  ground 
very  fine — the  finer,  the  better  the  finish  will  be  and  the  easier 
to  handle,  when  putting  on  the  designs.  At  any  rate,  the  in- 
gredients must  be  fine  enough  to  be  mixed  thoroughly,  as  if 
too  coarse  the  ingredients  in  the  paint  would  divide ;  that  is, 
the  silver,  glass  and  flint  being  very  coarse  would  not  combine 
correctly  with  the  other  powdered  ingredients.  A  gooo!  way 
to  grind  the  paint,  which  saves  the  cost  of  a  paint  mill  and 
is  just  as  satisfactory,  is  to  make  a  small  barrel  with  wooden 
strips,  that  will  hold  a  common  quart  fruit  jar,  and  is  made 
in  the  form  of  a  tumbling  barrel.  This  is  run  by  simply 
placing  a  belt  over  the  shafting  and  around  the  barrel.  Place 
the  paint  in  the  jar  with  about  fifteen  or  sixteen  glass  marbles 
of  different  sizes,  from  one-half  to  one  inch  in  diameter.  Do 
not  make  the  paint  too  thin  ;  cover  the  jar  tightly,  place  it 
inside  of  the  barrel  and  pack  around  with  old  cloth  or  rags,  to 
stop  the  jarring  or  breaking  of  the  jar.  Let  the  barrel  run  for 
a  day  or  two.  The  marbles  will  grind  the  paint  to  a  fineness, 
without  any  cost  for  labor,  that  could  not  be  obtained  by  hand 
in  several  hours.  After  the  paint  is  ground  fine  enough,  let 
it  settle  to  bottom  of  jar,  and  pour  off  the  surplus  turpentine. 
This  paint  (take  only  what  is  required  for  four  or  five  hours' 
work,  so  that  there  will  be  no  waste)  is  then  mixed  with  "fat 
oil  of  turpentine  "  (about  one  part  of  oil  to  five  or  six  parts  of 
paint)  on  a  glass  surface  or  artist's  palette  with  a  palette  knife  ; 
then  thin  to  proper  consistency  with  oil  of  turpentine  by  dip- 


654  ELECTRO-DEPOSITION    OF    METALS. 

ping  the  decorating  brush  in  same  and  working  it  out  on  the 
palette.  The  paint  should  be  mixed  or  stirred  up  regularly 
while  in  the  act  of  decorating,  to  keep  it  uniform  ;  as  the  oil 
comes  to  the  top,  and  as  the  color  of  the  paint  is  brownish,  it 
would  be  hard  to  tell  whether  the  lines  were  painted  with 
simply  the  oil  or  the  paint  body. 

Firing. — The  second  operation  is  the  firing,  which  proceeds 
as  follows :  After  the  work  is  decorated  let  it  stand  five  or  six 
hours  before  firing,  so  that  it  is  partly  dry  ;  then  place  in  the 
oven,  light  one  burner  of  the  gas  oven  (which  is  generally  used 
for  this  class  of  work) ;  light  a  second  burner  in  about  five 
minutes,  and  the  rest  of  the  burners  at  about  the  same  inter- 
vals, so  that  the  heat  will  start  gradually,  and  not  make  the 
paint  blister  or  crack,  which  would  be  the  case  if  a  strong  heat 
was  applied  too  quickly.  After  all  the  burners  are  started,  it 
will  take  from  one  to  one  and  one-half  hours  to  fire  work, 
according  to  size  of  oven  used,  but  the  operator  will  have  to 
try  a  few  pieces,  then  use  his  own  judgment  as  to  when  work 
is  properly  fired.  After  four  or  five  trials  he  should  be  able 
to  get  correct  results.  The  oven  should  be  in  a  dark  place,  or 
in  a  room  that  can  be  darkened  when  the  oven  is  in  use,  so 
that  the  operator  can  get  the  right  light  (when  looking  at  the 
work  being  fired)  through  the  openings  in  door  of  oven  to  see 
if  proper  heat  is  at  hand.  Heat  the  oven  until  the  bottom, 
top  and  sides  are  at  a  cherry-red  heat,  when  the  paint  is  then 
properly  fused  into  the  glass.  Turn  off  the  gas  quickly  by 
shutting  off  the  cock  in  the  feed-pipe,  then  let  the  work  cool 
off  gradually.  Do  not  open  the  door  of  the  oven  for  some 
time — two  or  three  hours — as  the  cold  current  of  air  would 
crack  the  hot  glass.  When  cool  enough  to  handle,  take  out 
carefully  ;  keep  the  fingers  or  hands  off  the  painted  parts,  as 
they  would  leave  marks  on  the  paint,  which  would  be  liable 
to  blister  when  plating. 

Now  wire  the  work  by  making  connections,  directly  on  the 
painted  parts.  Some  designs  which  are  not  connected  will, 
of  course,  have  to  have  a  separate  wire  on  each  part,  but  most 


GALVANOPLASTY  (REPRODUCTION).  655 

designs  are  made  so  that  one  connection  is  all  that  is  re- 
quired. After  the  work  is  wired,  it  is  then  ready  for  the  plat- 
ing bath  without  any  other  process  of  cleaning,  brushing  or 
striking  up.  As  the  silver  must  be  deposited  very  slowly,  it 
takes  between  twelve  to  twenty-four  hours  for  a  proper  deposit, 
according  to  the  grade  of  work,  the  articles  which  have  to  be 
engraved  to  bring  out  the  designs  taking  the  longer  time,  as 
all  that  is  required  for  plain  or  scroll  designs  is  just  enough 
silver  to  stand  the  finishing  operations.  The  plating  solution 
should  be  composed  of  not  less  than  6  ounces  silver,  and  not 
more  than  1  or  1J  ounces  of  free  cyanide  to  the  gallon.  If 
the  solution  is  too  light  in  metal  or  too  strong  in  cyanide,  the 
work  will  be  very  hard  to  finish,  and  the  silver  being  too 
brittle  would  raise  up  from  the  edges  of  the  painted  surface  in 
the  solution  or  in  the  finishing.  As  it  requires  such  a  long 
time  for  plating,  it  is  really  necessary  to  run  plating  baths 
with  storage  batteries  during  the  night  to  make  any  headway, 
that  is,  run  the  dynamo  while  the  power  is  going,  then  switch 
on  to  the  batteries  until  the  work  is  fully  plated.  Thus  the 
work  does  not  have  to  be  removed  from  the  plating  tank  at 
night  and  returned  to  solution  the  next  day,  as  that  would 
require  the  cleaning,  rewiring  and  striking  up  of  the  work  in 
order  not  to  have  any  failed  or  peeled  pieces.  Every  particle 
of  space  in  the  plating  tank  should  be  utilized  in  order  to  get 
in  as  many  pieces  of  work  as  possible  in  every  batch,  and 
twenty-five  to  thirty  amperes  are  all  that  are  required  for  a 
batch  of  seventy-five  or  eighty  pieces  of  mixed  work;  as  the 
plating  surface  is  very  small  even  with  a  full  batch  of  work. 
After  the  work  is  plated  it  is  then  sand-buffed,  cut  down  with 
tripoli  or  other  cutting-down  rouge,  washed  in  benzine,  en- 
graved, then  colored  in  the  usual  way  ;  that  is,  finished,  the 
same  as  sterling  or  silver-plated  hollow  ware.  The  quality  of 
glass  used  must  also  be  considered,  for  some  glass  will  turn 
yellow  before  the  proper  heat  is  reached  to  fuse  the  paint,  or 
else  will  get  out  of  shape  during  the  firing.  Imported  glass 
always  gives  best  results,  while  thin  articles  of  American  glass 


656  ELECTRO-DEPOSITION    OF    METALS. 

are  fairly  satisfactory.  The  heavy,  thick  glass  gives  very  poor 
results.  China  will  stand  and  requires  more  heat  in  firing 
than  glass,  so  it  is  advisable  to  fire  china  and  glass  separately 
to  obtain  the  best  results. 

Umbrella  and  cane  handles  of  celluloid  are  decorated  with  a 
metallic  deposit  by  means  of  galvanoplasty.  The  simplest 
mode  of  metallizing  them  is  to  paint  the  decorations  with  a 
mixture  of  bronze  powder  and  acetone.  On  the  point  of  con- 
tact, the  acetone  dissolves  a  small  quantity  of  celluloid,  the 
latter  thus  becoming  quite  firmly  united  with  the  bronze  pow- 
der. After  drying,  an  excess  of  non-adhering  powder  is  re- 
moved with  a  brush,  and  the  objects  are  then  brought  into  the 
copper  bath. 

Baby-shoes  for  a  keep-sake,  are  coppered  by  galvanoplasty, 
and  the  deposit  is  patinized  or  silvered.  Metallization  is  best 
effected  by  applying  several  coats  of  copal  lacquer,  and  black- 
leading  the  layer  of  lacquer  on  the  outside,  while  the  inside, 
which  is  more  difficult  of  access,  is  made  conductive  by  means 
of  bronze  powder  or  by  the  wet  way. 

Carbon  pins  and  carbon  blocks  for  electro-technical  purposes 
are  frequently  coated  with  copper  in  order  to  effect  a  more 
sure  metallic  contact  in  their  mountings.  The  carbons  are 
impregnated  with  wax  so  as  to  prevent  the  blue  vitriol  solu- 
tion from  penetrating.  They  are  then  brushed  with  quick- 
lime and  without  further  preparation  brought  into  the  bath. 

Rolls  of  steel  and  cast-iron,  pump-pistons,  etc.,  are  first  pro- 
vided with  as  thick  a  deposit  as  possible  in  the  cyanide  cop- 
per bath  and  then  brought  into  the  galvanoplastic  acid  copper 
bath.  With  a  bath  at  rest  the  current-density  should  not  ex- 
ceed 30  amperes  per  square  meter,  but  with  an  agitated  bath 
up  to  120  amperes  may  be  used. 

Steel  gun  barrels  for  marine  purposes  are  treated  in  the  same 
manner,  after  all  the  portions  which  are  not  to  receive  a  de- 
posit of  copper,  have  been  thoroughly  covered  with  a  mixture 
of  wax,  mastic  and  red  lead. 

Candelabra,  stairs  and  structural  parts  of  buildings  of  rough 


GALVANOPLAbTY    (REPRODUCTION).  657 

castings  require  a  somewhat  modified  treatment.  While  the 
rolls  and  steel  gun-barrels  previously  referred  to  are  always 
turned  smooth,  rough  iron  castings  are  used  for  the  above- 
mentioned  purposes,  and  the  production  in  the  potassium 
cyanide  bath  of  a  copper  deposit  of  such  thickness  as  not  to 
corrode  the  basis-metal  in  the  acid  copper  bath  is  frequently 
connected  with  difficulties.  In  a  plant  recently  furnished  by 
Dr.  Geo.  Langbein  &  Co.  for  coppering  rust-proof,  and  then 
brassing  structural  parts  of  a  postoffice  building  in  Mexico, 
the  following  plan  was  adopted  :  The  rough  castings  were  first 
carefully  cleaned  by  means  of  a  sand  blast  and  then  heavily 
nickeled ;  upon  this  nickel  coating  the  1  millimeter  thick  cop- 
per deposit  could  without  risk  be  produced  in  the  acid  copper 
bath.  The  parts  were  then  thoroughly  rinsed,  dried,  bright- 
ened with  a  brush  and  emery  and,  after  carefully  freeing  from 
grease,  electrolytically  provided  with  a  heavy  deposit  of 
bronze,  and  patinized. 

It  is  believed  sufficient  examples  of  the  uses  of  galvanoplasty 
have  here  been  given.  It  allows  of  the  most  varied  applica- 
tions, and  by  studying  the  special  processes  described  above, 
the  reader  will  be  in  a  position  to  find  out  the  most  suitable 
method  for  every  other  contingency. 

II.  GALVANOPLASTY  IN  IRON  (STEEL). 

Under  "  Deposition  of  Iron,"  the  galvanoplastic  produc- 
tion of  heavy  detachable  deposits  of  iron  has  already  been 
referred  to. 

Serviceable  iron  electrotypes  were  first  produced  about  1870, 
by  Klein  of  St.  Petersburg,  and  used  for  printing  Russian  bank 
notes.  Their  preparation  was,  and  is  still,  very  troublesome, 
success  depending  on  the  fulfillment  of  many  conditions,  so 
that,  notwithstanding  continued  experiments  and  the  expense 
of  much  labor,  the  former  expectation  of  entirely  supplanting 
electrotypes  in  copper  by  cliches  in  steel  has  thus  far  not  been 
realized. 

The  bath  used  by  Klein,  and  still  employed  for  this  purpose, 
42 


658  ELECTRO-DEPOSITION    OF    METALS. 

consists  of  a  10  per  cent,  solution  of  a  mixture  of  equal  parts 
of  ferrous  sulphate  (green  vitriol)  and  magnesium  sulphate 
(Epsom  salt).  The  solution  has  a  specific  gravity  of  1.05.  To 
obtain  successfully  a  serviceable  electrotype  from  an  original, 
for  instance,  from  a  copper  plate,  which  should  previously  be 
silvered  and  coated  with  a  thin  layer  of  silver  sulphide  by 
means  of  sulphuretted  hydrogen,  the  following  conditions  have 
to  be  fulfilled,  according  to  Klein's  statement:  The  bath  must 
be  kept  absolutely  neutral,  which  is  effected  by  suspending  in 
it  linen  bags  filled  with  magnesium  carbonate,  and  the  cur- 
rent-strength must  be  so  regulated  that  absolutely  no  evolution 
of  hydrogen  is  perceptible  on  the  anodes.  Further,  the  plates 
are  every  half  hour  to  be  taken  from  the  bath  and  rinsed  with 
a  powerful  jet  of  water  to  remove  any  adhering  gas-bubbles. 
Care  must  be  taken  during  this  process  that  the  plates  do  not 
become  dry,  since  fresh  layers  do  not  adhere  well  upon  plates 
which  have  become  dry. 

For  the  removal  of  adhering  gas-bubbles,  it  has  also  been 
proposed  frequently  to  pass  a  feather  over  the  plates. 

It  may  here  be  mentioned  that  Lenz  found  a  not  incon- 
siderable content  of  hydrogen  in  iron  deposits,  and  also  car- 
bonic acid,  carbonic  oxide  and  nitrogen  in  varying  quantities. 
However,  examinations  made  by  Dr.  Geo.  Langbein  estab- 
lished positively  only  a  content  of  hydrogen,  and  it  would 
seem  that  this  hydrogen,  which  is  absorbed  and  tenaciously 
retained  by  the  deposit,  is  the  cause  of  all  the  difficulties 
encountered  in  the  production  of  heavy  iron  deposits. 

If,  however,  the  occlusion  of  hydrogen  is  regarded  as  the 
cause  of  the  mischief,  ways  and  means  to  counteract  it  as  much 
as  possible  may  be  found  in  the  fact  that  iron  deposited  with 
greater  current-density  is  more  brittle,  shows  a  greater  ten- 
dency to  peel  off  in  the  bath,  and  contains  a  larger  quantity 
of  hydrogen  than  a  deposit  produced  with  slighter  current- 
density. 

In  this  respect  experience  gained  in  the  electrolytic  refining 
of  copper  shows  us  the  way  in  so  far  that  for  the  production 


GALVANOPLASTY  (REPRODUCTION).  659 

of  heavy  deposits  of  iron,  the  bath  must  be  kept  in  constant, 
vigorous  agitation,  to  remove,  on  the  one  hand,  layers  of  fluid 
poorer  in  metal  from  the  cathode,  and,  on  the  other,  to  force, 
by  the  agitation,  the  gas-bubbles  adhering  to  the  cathode  to 
escape.  Further,  deposition  must  be  effected  with  so  slight  a 
current-density  that  no  evolution  of  hydrogen  is  perceptible 
on  the  cathode,  and  a  current-density  of  0.25  ampere  may  be 
designated  as  the  maximum  per  15J  square  inches,  with  which 
heavy  deposits  of  iron  can  be  produced. 

To  counteract  the  spoiling  of  the  deposits,  further  precau- 
tionary measures  are,  however,  necessary,  especially  heating 
the  electrolyte,  and  from  time  to  time  interrupting  the  current. 
In  heated  baths  the  escape  of  the  gas  is  facilitated,  especially 
when  the  electrolyte  is  agitated,  and  hence  adhering  gas- 
bubbles  cannot  remain  long  in  one  place.  A  constantly-re- 
peated interruption  of  the  current  is  of  advantage  and  effective, 
because  metallic  parts  covered  with  a  minimum  quantity  of 
hydrogen  cannot  be  coated  with  a  fresh  deposit  until  the  hy- 
drogen is  removed  by  the  agitation  of  the  heated  electrolyte. 
Hence  the  interruption  of  the  process  of  deposition  would  give 
opportunity  and  time  for  the  removal  of  the  gas  molecules 
before  further  deposition  takes  place,  and  without  a  knowledge 
of  the  more  intimate  processes,  Klein  succeeded  in  affecting 
the  interruption  of  the  deposit,  by  taking  the  plates  at  short 
intervals  from  the  bath  and  removing  the  adhering  gas  by  a 
powerful  jet  of  water. 

With  the  present  state  of  galvanoplasty  it  is  not  necessary 
to  follow  Klein's  primitive  method,  and  it  would  be  more  prac- 
tical to  provide  the  positive  conducting  rod  of  the  bath  with  a 
contrivance  which  mechanically  effects  the  interruption  of  the 
current.  Suppose  upon  such  a  metallic  conducting  rod  is 
mounted  a  copper  or  brass  wheel,  which  is  secured  to  a  pulley 
and  revolves  around  the  conducting  rod,  and  half  of  the 
periphery  of  which  is  insulated,  and  that  upon  the  rod  drags 
a  metallic  brush  which  effects  the  transmission  of  the  positive 
current.  Now,  it  will  be  seen  that  while  the  contact-wheel  is 


660  ELECTRO-DEPOSITION    OF    METALS. 

revolving,  current  is  introduced  only  one-half  the  time  and 
not  during  the  other  half,  and  that  by  the  rapidity  of  revolu- 
tion of  the  contact-wheel,  the  number  of  interruptions  of  the 
current  can  be  varied  at  will. 

Since  Neubeck  has  in  a  relatively  very  short  time  produced 
in  hot  baths,  deposits  1  to  2  millimeters  thick,  of  coherent 
form  and  good  quality,  the  possibility  is  presented  of  making 
steel  electrotypes  in  an  indirect  way  by  obtaining  first  from 
the  impression  a  copper  electrotype,  from  this  a  negative  in 
copper,  and  after  silvering  the  latter,  producing  a  heavy 
deposit 'of  steel  upon  it. 

It  may  also  be  expected  that  by  complying  with  the  above- 
mentioned  conditions  and  the  discovery  of  new  methods,  it 
will  be  possible  directly  to  produce  steel  electrotypes  upon 
moulds  of  gutta-percha  or  wax  as  is  now  successfully  done 
with  nickel. 

It  is  well  known  that  electrolytically  deposited  iron  pos- 
sesses great  hardness,  and  that  such  deposits  well  deserve  the 
name  of  steel  deposits,  their  hardness  being  greater  than  that 
of  iron,  and  approaching  that  of  steel.  This  feature  cannot 
be  explained  otherwise  than  by  the  hydrogen  absorbed  by  the 
deposit.  Hence  it  will  be  seen  that,  on  the  one  hand,  this 
absorption  of  hydrogen  has  an  injurious  effect  upon  the  sep- 
aration of  iron,  while,  on  the  other,  it  imparts  to  the  deposits 
the  most  valuable  property  of  great  hardness.  It  would  seem 
that  the  quantities  of  iron  first  deposited  upon  the  mould  are, 
and  can  be,  richer  in  hydrogen  in  order  to  impart  to  the 
printing  surface  the  utmost  possible  hardness.  However,  in 
further  strengthening  and  augmenting  the  deposit,  our  efforts 
must  be  directed,  by  the  reduction  of  the  current,  to  deposit 
strengthening  layers  as  free  from  hydrogen  as  possible. 

The  question  now  arises,  whether  it  is  of  greater  advantage 
to  steel  a  copper  electrotype  in  order  to  increase  its  power  of 
resistance,  or  whether  it  is  better  to  produce  an  iron  electrotype 
and  to  strengthen  its  back  in  the  acid  copper  bath.  If  the 
above  expressed  view  that  the  layers  of  iron  first  deposited  are 


GALVANOPLASTY    (REPRODUCTION).  "661 

richer  in  hydrogen,  and  therefore  harder,  is  correct,  the  prefer- 
ence must  be  given  to  iron  electrotypes,  because  with  steeled 
copper  electrotypes  the  softer  layers  are  exposed  to  wear,  while 
the  harder  layers  lie  upon  the  copper  plate.  The  reverse 
is  the  case  with  an  iron  electrotype,  the  first  deposit,  rich  in 
hydrogen,  forming  the  printing  face. 

However,  on  the  other  hand,  steeled  copper  electrotypes 
have  the  advantage  that,  when  worn,  the  old  deposit  of  iron 
can  be  readily  removed  by  dilute  sulphuric  acid,  and  the  elec- 
trotypes resteeled,  while  worn  iron  electrotypes  have  to  be 
renewed. 

III.  GALVANOPLASTY  IN  NICKEL. 

Although  by  the  electro-deposition  of  nickel,  electrotypes  are 
rendered  fit  for  printing  with  metallic  colors,  which  attack  cop- 
per, and  their  power  of  resisting  wear  is  increased,  the  latter 
advantage  can  to  the  fullest  extent  be  obtained  only  by  a  thick 
deposit.  However,  this  always  alters  the  design  somewhat, 
especially  the  fine  hatchings,  this  being  the  reason  why  in 
nickel-plating  electrotypes  a  deposit  of  medium  thickness  is  as 
a  rule  not  exceeded.  If  a  hard  nickel  surface  is  desired,  with- 
out injury  to  the  fine  lines  of  the  design,  the  layer  of  nickel 
has  to  be  produced  by  galvanoplasty,  and  the  deposit  of  nickel 
strengthened  in  the  copper  bath. 

But  upon  black-leaded  gutta-percha  or  wax  moulds  a  nickel 
deposit  can  only  be  obtained  in  fresh  baths.  The  deposit, 
however,  is  faultless  only  in  rare  cases,  it  generally  showing 
holes  in  the  depressions.  Hence  the  object  has  to  be  attained 
in  a  round  about  way,  the  mode  of  procedure  being  as  follows  : 
An  impression  of  the  original  is  taken  in  gutta-percha  or  wax, 
and  from  this  impression  a  positive  cliche  in  copper  is  made. 
The  latter  is  then  silvered,  the  silvering  iodized  as  previously 
described,  and  a  negative  in  copper  is  then  prepared  from  this 
positive.  The  negative  is  again  silvered,  iodized,  and  then 
brought  into  a  nickel  bath,  where  it  receives  a  deposit  of  the 
thickness  of  stout  writing  paper.  It  is  then  rinsed  in  water, 


662  ELECTRO-DEPOSITION    OF    METALS. 

and  the  deposit  immediately  strengthened  in  the  acid  copper 
bath.  For  the  rest,  it  is  treated  like  ordinary  copper  deposits. 

If  for  the  production  of  the  nickel  electrotype,  a  nickel  bath 
of  the  composition  given  on  p.  266  and  heated  to  between 
185°  and  194°  F.  is  used,  deposition  may  be  made  with  high 
current-densities — 5  amperes  and  eventually  more — so  that  a 
thickness  of  0.2  millimeter  is  in  about  2J  hours  attained. 
This  deposit  is  slightly  coppered  in  the  acid  copper  bath  and 
backed. 

In  this  manner  nickel  electrotypes  of  15.74  X  11.81  inches 
have  been  produced,  but  as  will  be  seen  for  the  purposes  of 
printing  houses,  the  process  is  too  troublesome  and  time-con- 
suming, by  reason  of  the  necessary  production  of  the  copper 
matrices.  Hence  the  direct  method  of  deposition  upon  black- 
leaded  gutta-percha  or  wax  moulds  is  decidedly  to  be  preferred. 

This  direct  method  requires  a  cold  nickel  bath,  which  yields 
heavy  deposits  without  the  nickel  rolling  off,  and  for  deposits 
of  a  thickness  suitable  for  printing,  a  few  contrivances  to  pre- 
vent spontaneous  detachment  of  the  nickel  from  the  matrix. 
The  electrolyte,  according  to  patent  No.  134736  given  on  page 
267  is  applicable  to  this  purpose.  With  this  electrolyte,  de- 
posits of  6  millimeters'  thickness  were*  without  trouble  pro- 
duced at  the  ordinary  temperature  upon  gutta-percha.  In 
testing  other  nickel  baths  described  or  patented,  not  a  single 
one  was  found  which  allowed  of  obtaining  useful  nickel  de- 
posits directly  upon  the  matrices,  the  nickel  always  rolling 
off,  and  when  the  latter  drawback  was  prevented  by  suitable 
means,  it  was  impossible  to  obtain  a  deposit  of  more  than  0.05 
millimeter  thickness,  cracks  being  formed  in  the  center. 

In  working  with  this  direct  process  of  deposition,  it  is  abso- 
lutely necessary  always  to  keep  the  nickel  bath  slightly  acidu- 
lated, because  in  a  neutral  or  alkaline  electrolyte  the  deposit 
becomes  readily  rough  and  forms  with  a  dark  color,  which  is 
an  indication  of  the  formation  of  sponge.  It  is  also  of  advan- 
tage to  keep  the  electrolyte  constantly  agitated.  By  reason  of 
the  oxidation  of  the  ethyl-sulpho  combinations  which  takes 


GALVANOPLASTY    (REPRODUCTION). 


663 


place,  agitation,  however,  must  not  be  effected  by  blowing  in 
air,  but  by  mechanical  means,  or  eventually  by  blowing  in 
carbonic  acid. 

An  electro-motive  force  of  2.2  volts  and  a  current-density  of 
0.2  to  0.3  ampere  proved  most  suitable  for  the  production  of 
the  above-mentioned  nickel  electrotypes  of  6  millimeters  in 
thickness.  The  current  output — about  70  per  cent. — was  not 
particularly  favorable,  this  being,  however,  of  little  importance 
as  compared  with  the  advantages  offered  by  the  use  of  this 
electrolyte. 

It  has  previously  been  mentioned   that  in  order  to  obtain 


FIG.  152. 


FIG.  154. 


FIG.  155. 


FIG.  153. 


deposits  of  greater  thickness  upon  gutta-percha  or  wax,  a  few 
contrivances  are  required  to  prevent  the  deposit  from  rolling 
off.  With  the  use  of  gutta-percha  matrices  there  is  less  danger 
of  rolling  off  than  with  that  of  wax  moulds,  the  tendency  to 
rolling  off  being  much  earlier  shown  by  the  latter.  However, 
in  order  to  prevent  failures,  it  is  advisable  not  to  omit  these 
devices  even  when  working  with  gutta-percha  matrices. 

According  to  the  patent  specification,  a  groove  undercut 
towards  the  design  and  at  a  distance  of  about  3  millimeters 
from  it,  is  made  all  round,  and  another  such  groove  at  a  further 
distance  of  about  3  millimeters,  as  shown  in  Fig.  152  in  front 
view,  and  in  Fig.  153  in  section. 


664  ELECTRO-DEPOSITION    OP    METALS. 

The  object  of  this  contrivance  is  that  upon  the  carefully 
black-leaded  grooves,  nickel  continuous  with  the  nickel  upon 
the  design  is  also  deposited,  and  by  reason  of  the  undercutting 
towards  the  design  the  nickel  is  thus  prevented  from  rolling 
off  or  becoming  detached  if,  in  consequence  of  the  occlusion  of 
hydrogen,  the  deposit  shows  a  tendency  to  bend  up. 

According  to  the  above-mentioned  patent,  the  same  effect 
may  also  be  attained  by  firmly  securing  a  metallic  edge  all 
round  the  design.  While  the  nickel  deposit  cannot  become  inti- 
mately attached  to  the  black-leaded,  but  otherwise  non-metallic 
surfaces  of  the  gutta-percha  or  wax  matrices,  it  adheres  very 
firmly  to  the  metallic  edge,  rolling  off  being  thus  prevented. 
Dr.  Langbein  used  thin  brass  strips,  0.1  millimeter  thick  and 
5  millimeters  wide  which,  as  shown  in  Figs.  154  and  155,  were 
secured  by  small  pins  either  to  the  impressed  surface  or  to  the 
sides.  Wires  wound  round  the  four  sides  of  the  matrix  and 
lying  everywhere  closely  upon  its  black-leaded  surface,  may  be 
used  in  place  of  metal  strips.  It  is  advisable  to  place  the 
metal  strips  in  a  heated  state  upon  the  matrix  and  press  them 
gently  into  the  matrix-material  so  that  their  surfaces  lie  per- 
fectly level  with  the  surface  of  the  impression.  The  matrix 
and  the  metal  edge  having  been  carefully  black-leaded,  the 
outside  of  the  latter  is  brushed  over  with  a  rag  moistened  with 
potassium  cyanide  solution,  care  being  taken  not  to  damage 
the  black-leading  of  the  metal  towards  the  design.  Then  rinse 
the  matrix  with  alcohol  and  suspend  it  at  once  in  the  nickel 
bath,  the  latter  being  kept  at  rest  until  the  matrix  is  covered, 
and  then  agitated. 

Nickel  matrices. — In  casting  type  from  copper  matrices,  the 
latter  oxidize  quite  rapidly,  in  consequence  of  which  the  edges 
and  lines  especially  lose  sharpness,  while  the  surfaces  become 
scarred.  As  early  as  1883,  Weston  mentions  in  his  English 
patent  4784,  the  possibility  of  obtaining  heavy  deposits  of  solid 
nickel,  and  that  this  invention  is  valuable  for  the  production 
of  electrotypes,  which  without  doubt  includes  electrolytically 
prepared  matrices  for  casting  type,  the  influence  of  the  tern- 


GALVANOPLASTY  (REPRODUCTION).  665 

perature  of  the  liquid  metal  upon  such  nickel  matrices  being 
so  slight  that  they  do  not  warp,  etc. 

Notwithstanding  the  fact  that  thus  the  employment  of  an 
electrolytically-produced  casting  matrix  of  nickel  was  known, 
the  "  Aktien-Gesellschaft  fur  Schriftgiesserei  "  obtained  a  pat- 
ent, the  characteristic  feature  of  which  is  that  zinc  can  be 
directly  cast  around  the  face  "  without  further  galvanoplastic 
reinforcement." 

Hence  the  above-mentioned  patent  cannot  include  such 
nickel  matrices  in  which  by  the  deposition  of  nickel  the  face 
is  produced  of  a  thickness  which  by  itself  is  insufficient  to 
allow  of  the  deposit  being  detached  from  the  original  without 
fear  of  bending  or  breaking,  the  deposit  requiring  absolutely 
to  be  reinforced  to  the  customary  thickness  by  a  galvano- 
plastic deposit  of  copper.  It  is  obvious  that  a  thickness  of 
0.1  to  0.25  millimeter  of  nickel  suffices  to  withstand  the 
effect  of  temperature  and,  when  reinforced  by  copper,  also  the 
pressure  in  casting  in  the  machine.  Reinforcement  of  the 
casting  of  the  back  with  copper  has,  however,  the  further 
advantage  that  in  casting  zinc  around  the  face,  the  zinc  alloys 
to  a  certain  degree  with  the  copper  casting,  thus  uniting 
firmly  with  it,  which  is  not  the  case  when  zinc  is  cast  around 
the  pure  nickel  face  not  enveloped  by  copper,  nickel  not 
entering  into  a  solid  combination  with  zinc. 

Matrices  electrolytically  produced  from  cobalt  also  cannot 
be  claimed  under  the  above-mentioned  patent.  In  hardness, 
cobalt  is  equal  to  nickel  and  resists  the  hot  type-metal  as  well, 
possessing  therefore  all  the  properties  required  for  casting 
matrices. 

The  most  suitable  material  for  such  matrices  would  be  an 
alloy  of  nickel  and  cobalt  such  as  has  been  described  on  p. 
312  as  hard  nickel  alloy. 

In  order  to  effect  an  intimate  union  of  the  copper  casing 
with  the  nickel,  the  nickel  deposit  when  taken  from  the  nickel 
bath  has  to  be  brushed  over  with  nitric  acid,  rinsed,  and 
without  delay  brought  into  the  copper  bath. 


666  ELECTRO-DEPOSITION    OF    METALS. 

The  omission  of  these  manipulations,  which  require  dex- 
terity, may  have  been  the  cause  why  no  more  favorable  results 
were  obtained  by  former  experiments  to  reinforce  thinner 
nickel  deposits  by  copper  to  a  thickness  of  2  millimeters,  the 
nickel  deposits  becoming  detached  from  the  copper  when  the 
matrix  was  in  use.  If,  however,  in  accordance  with  the  sug- 
gestions given  above,  the  nickel  deposit  is  made  0.1  to  0.25 
millimeter  thick,  and  the  back,  which  is  to  be  reinforced, 
cleansed  with  nitric  acid  and  rinsed,  and  then  as  rapidly  as 
possible  brought  into  the  copper  bath  to  be  reinforced  to  2.5 
or  3  millimeters  in  thickness,  the  copper  will  adhere  firmly 
and  a  durable  matrix  will  be  obtained. 

By  means  of  galvanoplasty  matrices  of  massive  nickel  or 
cobalt  for  use  in  the  casting  machine  may  even  be  produced. 
However,  by  reason  of  their  hardness,  such  massive  nickel 
matrices  are  justified  with  difficulty,  and  besides  they  are  too 
expensive. 

While  no  experiments  for  the  production  of  nickel  matrices 
have  been  made  with  Weston's  baths,  nickel  deposits  several 
millimeters  in  thickness  can  without  doubt  be  made  with  them 
by  slightly  changing  their  composition  and  heating  them  to 
between  176°  and  194°  F.  In  the  experiments  made  baths  of 
the  composition  given  on  p.  266  were  used.  They  contained 
in  100  quarts,  77  Ibs.  of  nickel  sulphate  and  39.6  Ibs.  of  mag- 
nesium sulphate,  and  were  always  kept  slightly  acid  with 
acetic  acid,  the  temperature  during  deposition  being  as  con- 
stantly as  possible  maintained  at  194°  F. 

The  originals  have  to  be  prepared  in  a  manner  different 
from  that  for  matrices  in  copper.  In  place  of  wax  for  insulat- 
ing the  surfaces  which  are  to  receive  no  deposit,  a  material 
which  does  not  soften  at  194°  F.  has  to  be  used.  For  this 
purpose,  it  was  found  most  suitable  to  cast  plaster  of  Paris 
around  the  original,  or  a  paste  of  asbestos  meal  and  water- 
glass.  By  treatment  for  10  hours  in  the  hot  nickel  bath  dur- 
ing which  time  the  current  must  in  no  wise  be  interrupted, 
and  the  original,  especially  in  the  beginning,  be  vigorously 


GALVANOPLASTY    (REPRODUCTION).  667 

shaken,  a  nickel  deposit  about  0.25  millimeter  in  thickness  is 
obtained.  This  deposit,  as  previously  described,  is  reinforced 
in  the  acid  copper  bath  to  about  1.75  to  2.25  millimeters  in 
thickness,  and  zinc  having  in  the  usual  manner  been  cast 
around  it,  is  justified  for  the  casting  machine. 

The  production  of  nickel  matrices  may  also  be  effected  with 
the  use  of  the  cold  nickel  bath  described  on  p.  267,  but  much 
more  time  is  required.  In  this  case  the  originals  may  of  course 
be  insulated  with  wax. 

IV.  GALVANOPLASTY  IN  SILVER  AND  GOLD. 

The  preparation  of  reproductions  in  silver  and  gold  pre- 
sents many  difficulties.  While  copper  is  reducible  in  a  com- 
pact state  from  its  sulphate  solution,  silver  and  gold  have  to 
be  reduced  from  their  double  salt  solutions — potassium-silver 
cyanide  and  potassium-gold  cyanide.  However,  these  alka- 
line solutions  attack  moulds  of  fatty  substances,  such  as  wax 
and  stearine,  consequently  also,  plaster-of-Paris  moulds  im- 
pregnated with  these  substances,  as  well  as  gutta  percha  and 
gelatine.  Hence,  only  metallic  moulds  can  be  advantageously 
used,  unless  the  end  is  to  be  attained  in  a  round-about  way  ; 
that  is,  by  first  coating  the  mould  with  a  thin  film  of  copper, 
reinforcing  this  in  the  silver  or  gold  bath,  and  finally  dis- 
solving the  film  of  copper  with  dilute  nitric  acid. 

The  double  salt  solutions  mentioned  above  require  a  well- 
conducting  surface  such  as  cannot  be  readily  prepared  by 
black-leading,  a  further  reason  why  metallic  moulds  are  to  be 
preferred. 

The  simplest  way  for  the  galvanoplastic  reproduction  in  gold 
or  silver  of  surfaces  not  in  too  high  relief  or  too  much  under- 
cut, is  to  cover  the  object  with  lead,  silver  or  gold  foil,  and 
pressing  softened  gutta-percha  upon  it.  The  foil  yields  to  the 
pressure  without  tearing,  and  adheres  to  the  gutta-percha  so 
firmly  that  it  can  be  readily  separated  together  with  it.  This 
method  is  of  course  only  applicable  if  the  originals  to  be 
moulded  can  bear  the  pressure  of  the  press. 


668  ELECTRO-DEPOSITION    OF    METALS. 

With  originals  which  cannot  stand  pressure,  or  have  portions 
in  very  high  relief,  or  much  undercut,  oil  gutta-percha  may 
be  used.  The  original  secured  to  a  brass  plate,  having  been 
heated  to  between  122°  and  140°  F.  and  slightly  oiled,  the  oil 
gutta-percha  in  small  cubes  is  applied  so  that  one  cube  is  first 
placed  upon  the  original,  and,  when  soft,  pressed  firmly  down 
with  the  moistened  finger,  other  cubes  being  then  in  the  same 
manner  applied  until  the  entire  surface  of  the  original  is  cov- 
ered, when  the  whole  is  allowed  to  cool,  which  may  be  accel- 
erated by  placing  it  in  very  cold  water.  This  impression  can 
be  detached  in  good  shape  from  the  original  by  the  use  of  gen- 
tle force,  the  oil  gutta-percha  being  in  a  hardened  state  suffi- 
ciently pliable  to  allow  of  its  being  readily  taken  out  from  the 
undercut  portions.  The  face  of  the  mould  is  next  freed  from 
oil  by  means  of  alcohol,  or  by  brushing  with  liquid  ammonia, 
and  then  dried.  Now  powder  the  mould  with  fine  silver 
powder,  thoroughly  rubbing  the  latter  with  a  brush  into  the 
depressions,  so  that  it  adheres  firmly  to  the  gutta-percha,  and 
after  blowing  off  an  excess,  bring  the  mould  into  the  silver  bath. 

The  most  suitable  composition  of  the  galvanoplastic  silver 
bath  is  as  follows  : 

Fine  silver  (in  the  form  of  silver  cyanide)  1  j  ozs.,  99  per 
cent,  potassium  cyanide  4J  ozs.,  water  1  quart. 

Maximum  current-density,  0.3  amp&re. 

A  slighter  current-density  than  that  given  above  can  only 
be  beneficial,  and  the  electro-motive  force  should  be  as  low  as 
possible,  the  best  deposits  having  been  obtained  with  0.5  volt 
and  an  electrode-distance  of  10  centimeters. 

For  galvanoplasty  in  gold,  the  same  process  as  described 
above  is  used.  Good  results  are  obtained  with  a  bath  com- 
posed as  follows : 

Fine  gold  (in  the  form  of  neutral  chloride  of  gold  or  fulmi- 
nating gold)  1  oz.,  99  per  cent,  potassium  cyanide  3J  ozs., 
water  1  quart. 

Current-density,  0.1  ampere. 

Electro-motive  force  at  10  cm.  electrode-distance,  0.4  volt. 


CHAPTER  XVIII. 

CHEMICALS    USED     IN     ELECTRO-PLATING    AND     GALVANOPLASTY. 

BELOW  the  characteristic  properties  of  the  chemical  prod- 
ucts employed  in  the  workshop  will  be  briefly  discussed, 
and  the  reactions  indicated  which  allow  of  their  recognition. 
It  frequently  happens  that  the  labels  become  detached  from 
the  bottles  and  boxes,  thus  rendering  the  determination  of 
their  contents  necessary. 

I.   Adds. 

1.  Sulphuric  add  (oil  of  vitriol). — Two  varieties  of  this  acid 
are  found  in  commerce,  viz..  fuming  sulphuric  acid  (disul- 
phuric  acid)  and  ordinary  sulphuric  acid.  The  first  is  a  thick 
oily  fluid,  generally  colored  yellowish  by  organic  substances, 
and  emits  dense,  wh\te  vapors  in  the  air.  Its  specific  gravity 
is  1.87  to  1.89.  The  only  purpose  for  which  fuming  sulphuric 
acid  is  used  in  the  electro-plating  art,  is  as  a  mixture  with 
nitric  acid  for  stripping  silvered  objects. 

Ordinary  sulphuric  acid  has  a  specific  gravity  of  1.84. 
Diluted  with  water  it  serves  for  filling  the  Bunsen  elements 
and  as  a  pickle  for  iron  ;  in  a  concentrated  state  it  is  used  in 
the  preparation  of  pickles  and  as  an  addition  to  the  galvano- 
plastic  copper  bath.  The  crude  commercial  acid  generally 
contains  arsenic,  hence  care  must  be  had  to  procure  a  pure 
article.  In  diluting  the  acid  with  water,  it  should  in  all  cases 
be  added  to  the  water  in  a  very  gentle  stream  and  with  con- 
stant stirring,  as  otherwise  a  sudden  generation  of  steam  of 
explosive  violence  might  result,  and  the  dangerous  corrosive 
liquid  be  scattered  in  all  directions.  Concentrated  sulphuric 
acid  vigorously  attacks  all  organic  substances,  and  hence  has 

(669) 


670  ELECTRO-DEPOSITION    OF    METALS. 

to  be  kept  in  bottles  with  glass  stoppers,  and  bringing  it  in 
contact  with  the  skin  should  be  carefully  avoided. 

Recognition. — One  part  of  the  acid  mixed  with  25  parts  of 
distilled  water  gives,  when  compounded  with  a  few  drops  of 
barium  chloride  solution,  a  white  precipitate  of  barium  sul- 
phate. 

2.  Nitric  acid  (aqua  fortis,  spirit  of  nitre). — It  is  found  in 
trade  of  various  degrees  of  strength.     For  our  purposes,  acid 
of  40°  and  30°  Be.  is  generally  used.     The  acid  is  usually  a 
more  or  less  deep  yellow,  and  frequently  contains  chlorine. 
The  vapors  emitted  by  nitric  acid  are  poisonous  and  of  a  char- 
acteristic odor,  by  which  the  concentrated  acid  is  readily  dis- 
tinguished from  other  acids.     It  is  used  for  filling  the  Bunsen 
elements  (carbon  in  nitric  acid),  and  for  pickling  in  combina- 
tion with  sulphuric  acid  and  chlorine.     On  coming  in  contact 
with  the  skin  it  produces  yellow  stains. 

Recognition. — By  heating  the  not  too  dilute  acid  with  cop- 
per, brown-red  vapors  are  evolved.  For  the  determination  of 
dilute  nitric  acid,  add  a  few  drops  of  it  to  green  vitriol  solu- 
tion, when  a  black-brown  coloration  will  be  produced  on  the 
point  of  contact. 

3.  Hydrochloric  acid  (muriatic  acid). — The  pure  acid  is  a 
colorless  fluid  which  emits  abundant  fumes  in  contact  with 
the  air,  and  has  a  pungent  odor  by  which  it  is  readily  dis- 
tinguished  from    other  acids.      The  specific   gravity   of  the 
strongest  hydrochloric  acid   is  1.2.     The  crude  acid  of  com- 
merce has  a  yellow  color,  due  to  iron,  and  contains  arsenic. 
'Dilute  hydrochloric  acid  is  used  for  pickling  iron  and  zinc. 

Recognition. — On  adding  to  the  acid,  very  much  diluted 
with  distilled  water,  a  few  drops  of  solution  of  nitrate  of  silver 
in  distilled  water,  a  heavy  white  precipitate  is  formed,  which 
becomes  black  by  exposure  to  the  light. 

4.  Hydrocyanic  acid  (prussic  acid). — This  extremely  poison- 
ous acid  exists  in  nature  only  in  a  state  of  combination  in 
certain  vegetables  and  fruits,  and  especially  in  the  kernels  of 
the   latter,  as,  for  instance,  in  the  peach,  the  berries  of  the 


CHEMICALS    USED    IN    ELECTRO-PLATING.  671 

cherry  laurel,  bitter  almonds,  the  stones  of  the  apricot,  of 
plums,  cherries,  etc.  It  may  be  obtained  anhydrous,  but  in 
this  state  it  is  useless,  and  very  difficult  to  preserve  from  de- 
composition. Diluted  hydrocyanic  acid  is  colorless,  with  a 
bitter  taste  and  the  characteristic  smell  of  bitter  almonds.  It 
is  employed  in  the  preparation  of  gold  immersion  baths,  and 
for  the  decomposition  of  the  potassa  in  old  silver  baths.  The 
inhalation  of  the  vapors  of  this  acid  may  have  a  fatal  effect, 
as  also  its  coming  in  contact  with  wounds. 

Recognition. — By  its  characteristic  smell  of  bitter  almonds. 
Or  mix  it  with  potash  lye  until  blue  litmus  paper  is  no  longer 
reddened,  then  add  solution  of  green  vitriol  which  has  been 
partially  oxidized  by  standing  in  the  air,  and  acidulate  with 
hydrochloric  acid.  A  precipitate  of  Berlin  blue  is  formed. 

5.  Citric   acid. — Clear   colorless    crystals    of  1.542    specific 
gravity,  which  dissolve  with  great  ease  in  both  hot  and  cold 
water.     It  is  frequently  employed  for  acidulating  nickel  baths, 
and,  combined  with  sodium  citrate,  in  the  preparation  of  plati- 
num baths. 

Recognition. — Lime-water  compounded  with  aqueous  solu- 
tion of  citric  acid  remains  clear  in  the  cold,  but  on  boiling 
deposits  a  precipitate  of  calcium  citrate.  The  precipitate  is 
soluble  in  ammonium  chloride,  but  on  boiling  is  again  pre- 
cipitated, and  is  then  insoluble  in  sal  ammoniac. 

6.  Boric  acid  (boracic  acid}. — This  acid  is  found  in  commerce 
in  the  shape  of  scales  with  nacreous  luster  and  greasy  to  the 
touch  ;  when  obtained  from  solutions  by  evaporation,  it  forms 
colorless  prisms.     Its   specific  gravity   is   1.435;  it  dissolves 
with   difficulty   in   cold   water   (1    part  of  acid   requiring  at 
64.4°  F.  28  of  water),  but  is  more  rapidly  soluble  in  boiling 
water  (1  part  of  acid  requiring  3  of  water  at  212°  F.).    Accord- 
ing to   Weston's  proposition,  boric  acid   is  employed   as  an 
addition  to  nickel  baths,  etc. 

Recognition. — By  mixing  solution  of  boric  acid  in  water  with 
some  hydrochloric  acid  and  dipping  turmeric  paper  in  the 
solution,  the  latter  acquires  a  brown  color,  the  color  becoming 


672  ELECTRO-DEPOSITION    OF    METALS. 

more  intense  on  drying.  Alkalies  impart  to  turmeric  paper 
a  similar  coloration,  which,  however,  disappears  on  immersing 
the  paper  in  dilute  hydrochloric  acid. 

7.  Arsenious  acid  (ivhite  arsenic,  arsenic,  ratsbane). — It  gen- 
erally occurs  in  the  shape  of  a  white  powder,  and  sometimes 
in  %vitreous-like  lumps,  resembling  porcelain.     For  our  pur- 
poses the  white   powder  is  almost    exclusively   used.     It  is 
slightly  soluble  in  cold  water,  and  more  readily  so  in  hot  water 
and  hydrochloric  acid.     Notwithstanding  its  greater  specific 
gravity  (3.7),  only  a  portion  of  the  powder  sinks  to  the  bottom 
on  mixing   it  with  water,  another  portion  being  retained  on 
the  surface  by  air  bubbles  adhering  to  it.     It  is  employed  as 
an   addition   to  brass   baths,   further,   in   the  preparation   of 
arsenic    baths,    for    blacking   copper    alloys/  and    in    certain 
silver  whitening  baths. 

Recognition. — When  a  small  quantity  of  arsenious  acid  is 
thrown  upon  glowing  coals  an  odor  resembling  that  of  garlic 
is  perceptible.  By  mixing  solution  of  arsenious  acid,  prepared 
by  boiling  with  water,  with  a  few  drops  of  ammoniacal  solu- 
tion of  nitrate  of  silver,  a  yellow  precipitate  of  arsenate  of 
silver  is  obtained.  The  ammoniacal  solution  of  nitrate  of 
silver  is  prepared  by  adding  ammonia  to  solution  of  nitrate  of 
silver  until  the  precipitate  at  first  formed  disappears. 

8.  Chromic  acid. — It  forms  crimson-red  needles,  and   also 
occurs  in  commerce  in  the  shape  of  a  red  powder.     It  is  read- 
ily  soluble  in  water,  forming  a  red  fluid,  which   serves  for 
tilling  batteries. 

Recognition. —  Chromic  acid  can  scarcely  be  mistaken  for 
any  other  chemical  product  employed  by  the  electro-plater. 
A  very  much  diluted  solution  of  it  gives,  after  neutralization 
with  caustic  alkali  and  adding  a  few  drops  of  nitrate  of  silver 
solution,  a  crimson-red  precipitate  of  chromate  of  silver. 

9.  Hydrofluoric   acid. — A   colorless,   corrosive,    very   mobile 
liquid  of  a  sharp,  pungent  odor.     The  anhydrous  acid  fumes 
strongly  in  the  air  and  attracts  moisture  with  avidity.     Hydro- 
fluoric acid  is  used  for  etching  glass  and  for  pickling  alumin- 


CHEMICALS    USED    IN    ELECTRO-PLATING.  673 

ium  dead  white.  Great  care  must  be  observed  in  working 
with  the  acid,  since  not  only  the  aqueous  solution,  but  also 
the  vapors,  have  an  extremely  corrosive  effect  upon  the  skin 
and  respiratory  organs. 

Recognition. — By  covering  a  small  platinum  dish  containing 
hydrofluoric  acid  with  a  glass  plate  free  from  grease,  the  latter 
in  half  an  hour  appears  etched. 

II.  Alkalies  and  Alkaline  Earths. 

10.  Potassium  hydrate  (caustic  potash). — It  is  found  in  com- 
merce in  various  degrees  of  purity,  either  in  sticks  or  cakes. 
It  is  very  deliquescent,  and   dissolves  readily  in  water  and 
alcohol ;  by  absorbing   carbonic  acid   from  the  air  it  rapidly 
becomes  converted  into  the  carbonate,  and  thus  loses  its  caustic 
properties.     It  should,  therefore,  be  kept  in  well-closed  vessels. 
Substances  moistened  with  solution  of  caustic  potash  give  rise 
to  a  peculiar  soapy  sensation  of  the  skin  when  touched.     It 
should  never  be  allowed  to  enter  the  mouth,  as  even  dilute 
solutions  almost  instantaneously  remove  the  lining  of  tender 
skin.     Should  such  an  accident  happen,  the  mouth  should  at 
once  be  rinsed  several  times  with  water  and  then  with  very 
dilute  acetic  acid.     Pure  caustic  potash  serves  as  an  addition 
to  zinc  baths,  gold  baths,  etc.     For  the  purpose  of  freeing  ob- 
jects from  grease  the  more  impure  commercial  article  is  used. 

11.  Sodium  hydrate  (caustic  soda). — It  also  occurs  in  com- 
merce in  various  degrees  of  purity,  either  in  sticks  or  lumps. 
It  is  of  a    highly   caustic    character,   resembling   potassium 
hydrate  (see  above)  in  properties  and  effects.     It  is  employed 
for  freeing  objects  from  grease,  for  the  preparation  of  alkaline 
tin  and  zinc  baths,  etc. 

12.  Ammonium  hydrate  (ammonia  or  spirits  of  hartshorn). — 
It  is  simply  water  saturated  with  ammonia  gas.     By  exposure 
ammonia  gas  is  gradually  evolved,  so  that  it  must  be  kept  in 
closely-stoppered  bottles,  in  order  to  preserve  the  strength  of 
the  solution  unimpaired.     Four  qualities  are  generally  found 
in  commerce,  viz.,  ammonia  of  0.910  specific  gravity  (contain- 

43 


674  ELECTRO-DEPOSITION    OF    METALS. 

ing  24.2  per  cent,  of  ammonia  gas) ;  of  0.920  specific  gravity 
(with  21.2  per  cent,  of  ammonia  gas);  of  0.940  specific  gravity 
(with  15.2  per  cent,  of  ammonia  gas);  and  0.960  specific  grav- 
ity (with  9.75  per  cent,  of  ammonia  gas).  It  is  employed  for 
neutralizing  nickel  and  cobalt  baths  when  too  acid,  in  the 
preparation  of  fulminating  gold,  and  as  an  addition  to  some 
copper  and  brass  baths. 
Recognition. — By  the  odor. 

13.  Calcium  hydrate  (burnt  or  quick  lime). — It  forms  hard, 
white  to  gray  pieces,  which  on  moistening  with  water  crumble 
to  a  light  white  powder,  evolving  thereby  much  heat.     Vienna 
lime  is  burnt  lime  containing  magnesia.     Lime  serves  for  free- 
ing objects  from  grease,  and  for  this  purpose  is  made  into  a 
thinly-fluid  paste  with  chalk  and  water,  with  which  the  objects 
to  be  freed  from  grease  are  brushed.     Vienna  lime  is  much 
used  as  a  polishing  agent. 

III.  Sulphur  Combinations. 

14.  Sulphuretted    hydrogen   (sulphydric   acid,   hydrosulphuric 
acid). — A  very  poisonous,  colorless  gas  with  a  fetid  smell  re- 
sembling that  of  rotten  eggs.     Ignited  in  the  air,  it  burns  with 
a  blue  flame,  sulphurous  acid  and  water  being  formed.    At  the 
ordinary  temperature  water  absorbs  about  three  times  its  own 
volume  of  the  gas,  and  then  acquires  the  same  properties  as  the 
gas  itself.     Sulphuretted  hydrogen  serves  for  the  metallizing 
of  moulds  as  described  in  the  preceding  chapter,  where  the 
manner  of  generating  it  is  also  given.     It  is  sometimes  em- 
ployed for  the  production  of  "  oxidized  "  silver.     Care  should 
be  taken  not  to  bring  metallic  salts,  gilt  or  silvered  articles,  or 
pure  gold  and  silver  in  contact  with  sulphuretted  hydrogen, 
they  being  rapidly  sulphurized  by  it. 

Recognition. — By  its  penetrating  smell ;  further,  by  a  strip  of 
paper  moistened  with  sugar  of  lead  solution  becoming  black 
when  brought  into  a  solution  of  sulphuretted  hydrogen  or  an 
atmosphere  containing  it. 

15.  Potassium  sulphide  (liver  of  sulphur). — It  forms  a  hard 


CHEMICALS    USED    IN    ELECTRO-PLATING.  675 

green-yellow  to  pale-brown  mass,  with  conchoidal  fracture.  It 
readily  absorbs  moisture,  whereby  it  deliquesces  and  smells  of 
sulphuretted  hydrogen.  It  is  employed  for  coloring  copper 
and  silver  black. 

Recognition. — On  pouring  an  acid  over  liver  of  sulphur, 
sulphuretted  hydrogen  is  evolved  with  effervescence,  sulphur 
being  at  the  same  time  separated. 

16.  Ammonium  sulphide  (sidphydrate  or  hydrosulphate  of  am- 
monia).— When  freshly  prepared  it  forms  a  clear  and  colorless 
fluid,  with  an  odor  of  ammonia  and  sulphuretted  hydrogen  ; 
by  standing  it  becomes  yellow,  and,  later  on,  precipitates  sul- 
phur.    It  is  used  for  the  same  purpose  as  liver  of  sulphur. 

17.  Carbon  disulphide  or  bisulphide. — Pure  carbon  disulphide 
is  a  colorless  and  transparent  liquid  which  is  very  dense,  and 
exhibits  the  property  of  double  refraction.     Its  smell  is  char- 
acteristic and  most  disgusting,  and  may  be  compared  to  that  of 
rotten  turnips.     It  burns  with  a  blue  flame  of  sulphurous  acid, 
carbonic  acid  being  at  the  same  time  produced.     It  is  used  as 
a  solvent  for  phosphorus  and   rubber  in   metallizing  moulds 
according  to  Parkes'  method.     This  solution  should  be  very 
carefully  handled. 

18.  Antimony  sulphide. — a.  Black  sulphide  of  antimony  (sti- 
bium sulfuratum  nigrum)  is  found  in  commerce  in  heavy,  gray 
and  lusterless  pieces  or  as  a  fine  black-gray  powder,  with  slight 
luster.     It  serves  for  the  preparation  of  antimony  baths,  and 
for  coloring  copper  alloys  black. 

b.  Red  sulphide  of  antimony  (stibium  sulfuratum  aurantia- 
cum)  forms  a  delicate  orange-red  powder  without  taste  or  odor  ; 
it  is  insoluble  in  water,  but  soluble  in  ammonium  sulphide, 
spirits  of  hartshorn  and  alkaline  lyes.  In  connection  with 
ammonium  sulphide  or  ammonia  it  serves  for  coloring  brass 
brown. 

19.  Arsenic  trisulphide  or  arsenious  sulphide  (orpiment). — It 
is  found  in  commerce  in  the  natural,  as  well  as  artificial,  state, 
the  former  occurring  mostly   in   kidney-shaped   masses   of  a 
lemon  color,  and  the  latter  in  more  orange-red  masses,  or  as  a 


676  ELECTRO-DEPOSITION    OF    METALS. 

dull  yellow  powder.     Specific  gravity  3.46.     It  is  soluble  in 
the  alkalies  and  spirits  of  sal  ammoniac. 

20.  Ferric  sulphide. — Hard,  black  masses  generally  in  flat 
plates,  which  are  only  used  for  the  generation  of  sulphuretted 
hydrogen. 

IV.    Chlorine  Combinations. 

21.  Sodium  chloride  (common  salt,  rock  salt). — The  pure  salt 
should  form  white,  cubical  crystals,  of  which  100  parts  of  cold 
water  dissolve  36,  hot  water  dissolving  slightly  more.     The 
specific  gravity  of  sodium  chloride  is  2.2.     In  electroplating 
sodium  chloride  is  employed  as  a  conducting  salt  for  some 
gold  baths,  as   a  constituent  of  argentiferous  pastes,  and  for 
precipitating  the  silver  as  chloride  from  argentiferous  solutions. 

Recognition. — An  aqueous  solution  of  sodium  chloride  on 
being  mixed  writh  a  few  drops  of  lunar  caustic  solution,  yields 
a  white  caseous  precipitate,  which  becomes  black  by  exposure 
to  light,  and  does  not  dissappear  by  the  addition  of  nitric  acid, 
but  is  dissolved  by  ammonia  in  excess. 

22.  Ammonium  chloride  (sal  ammoniac). — A  white  substance 
found  in  commerce  in  the  shape  of  tough  fibrous  crystals.     It 
has  a  sharp  saline  taste,  and  is  soluble  in  2J  parts  of  cold,  and 
in  a  much  smaller  quantity  of  hot  water.     By  heat  it  is  sub- 
limed   without  decomposition.     It  serves  for  soldering  and 
tinning,  and  as  a  conducting  salt  for  many  baths. 

Recognition. — By  sublimation  on  heating.  By  adding  to  a 
saturated  solution  of  the  salt  a  few  drops  of  solution  of  platinum 
chloride,  a  yellow  precipitate  of  platoso-ammonium  chloride 
is  formed. 

23.  Antimony  trichloride  (butter  of  antimony}. — A  crystalline 
mass  which  readily   deliquesces  in  the  air.     Its  solution  in 
hydrochloric  acid   yields  the  liquor  stibii  chlorati,  also  called 
liquid  butter  of  antimony.     It  has  a  yellowish  color,  and  on 
mixing   with    water   yields   an   abundant    white    precipitate, 
soluble  in  potash  lye.     The  solution  serves  for  coloring  brass 
steel-gray,  and  for  browning  gun-barrels. 


CHEMICALS    USED    IN    ELECTRO-PLATING.  677 

24.  Arsenious  chloride. — A  thick,  oily  fluid,  which  evaporates 
in  the  air  with  the  emission  of  white  vapors. 

25.  Copper  chloride. — Blue-green  crystals  readily  soluble  in 
water.     The  concentrated   solution   is  green,  and  the  dilute 
solution    blue.       On    evaporating    to   dryness,    brown-yellow 
copper  chloride  is  formed.      It  is  employed   in   copper  and 
brass  baths  as  well  as  for  patinizing. 

26.  Tin  chloride. — a.  Stannous  chloride  or  tin  salt.     A  white 
crystalline  salt  readily  soluble  in  water,  but  its  solution  on 
exposure  to  the  air   becomes  turbid  ;    by   adding,   however, 
hydrochloric  acid,  it  again   becomes   clear.     On   fusing  the 
crystallized  salt  loses  its  water  of  crystallization,  and  forms  a 
solid  non-transparent  mass  of  a  pale  yellow  color — the  fused 
tin  salt.     The  crystallized,  as  well  as  the  fused,  salt  serves  for 
the  preparation  of  brass,  bronze  and  tin  baths. 

Recognition. — By  pouring  hydrochloric  acid  over  a  small 
quantity  of  tin  salt  and  adding  potassium  chromate  solution, 
the  solution  acquires  a  green  color.  By  mixing  dilute  tin 
salt  solution  with  some  chlorine  water  and  adding  a  few  drops 
of  gold  chloride  solution,  purple  of  Cassius  is  precipitated  ; 
very  dilute  solutions  acquire  a  purple  color. 

b.  Stannic  chloride  occurs  in  commerce  in  colorless  crystals. 
In  the  anhydrous  state  it  forms  a  yellowish,  strongly  fuming 
caustic  liquid  known  as  the  "  fuming  liquor  of  Libadius." 

27.  Zinc  chloride  (hydrochlorate  or  muriate  of  zinc;  butter  of 
zinc). — A  white  crystalline  or  fused  mass  which  is  very  solu- 
ble and  deliquescent.     The  salt  prepared  by  evaporation  gen- 
erally contains  some  zinc  oxychloride,  and   hence  does  not 
yield  an  entirely  clear  solution.     It  serves  for  preparing  brass 
and  zinc  baths,  and  its  solution  in  nickeling  by  immersion, 
soldering,  etc. 

Recognition. — Solution  of  caustic  potash  separates  a  volumi- 
nous precipitate  of  zinc  oxy hydrate,  which  redissolves  in  an 
excess  of  the  caustic  potash  solution.  By  conducting  sul- 
phuretted hydrogen  into  a  solution  of  a  zinc  salt  acidulated 
with  acetic  acid,  a  precipitate  of  white  zinc  sulphide  is  formed. 


678  ELECTRO-DEPOSITION    OF    METALS. 

28.  Chloride  of  zinc  and  ammonia. — This  salt  is  a  combina- 
tion of  zinc  chloride  and  ammonium  chloride,  and  forms  ver}^ 
deliquescent  crystals.     Its  solution  in  water  serves  for  solder- 
ing, and  zincking  by  contact. 

29.  Nickel  chloride. — It  is  found  in  commerce  in  the  shape 
of  deep  green  crystals  and  of  a  pale  green  powder.     The  latter 
contains  considerably  less  water  and  less  free  acid  than  the 
crystallized  article,  and  is  to  be  preferred  for  electro-plating 
purposes.     The  crystallized  salt  dissolves  readily  in  water,  and 
the  powder  somewhat  more  slowly.     Should  the  solution  of  the 
latter  deposit  a  yellow  precipitate,  consisting  of  basic  nickel 
chloride,  it  has  to  be  brought  into  solution  by  the  addition  of 
a  small  quantity  of  hydrochloric  acid.     Nickel  chloride  is  em- 
ployed for  nickel  baths. 

Recognition — By  mixing  the  green  solution  of  the  salt  with 
some  spirits  of  sal  ammoniac,  a  precipitate  is  formed,  which 
dissolves  in  an  excess  of  spirits  of  sal  ammoniac,  the  solution 
showing  a  deep  blue  color. 

30.  Cobaltous  chloride. — It  forms  small  rose-colored  crystals, 
which,  on  heating,  yield  their  water  of  crystallization,  and  are 
converted  into  a  blue  mass.     The  crystals  are  readily  soluble 
in  water,  while  the  anhydrous  blue  powder  dissolves  slowly. 
Cobalt  chloride  is  employed  for  the  preparation  of  cobalt  baths. 

Recognition. — Caustic  potash  precipitates  from  a  solution  of 
cobalt  chloride  a  blue  basic  salt  which  is  gradually  converted 
into  a  rose-colored  hydrate,  and,  with  the  access  of  air,  into 
green-brown  cobaltous  hydrate.  The  aqueous  solution  yields 
with  solution  of  yellow  prussiate  of  potash,  a  pale  gray-green 
precipitate. 

31.  Silver  chloride. — A  heavy  white  powder  which  by  ex- 
posure to  light  becomes  gradually  blue-gray,  then  violet,  and 
finally  black.     When  precipitated  from  silver  solutions,  a  case- 
ous precipitate  is  separated.     At  500°   F.   it  fuses,  without 
being  decomposed,  to  a  yellowish  fluid  which,  on  cooling,  con- 
geals  to   a   transparent,    tenacious,    horn-like    mass.     Silver 
chloride  is  practically  insoluble  in  water,  but  dissolves  with 


CHEMICALS    USED    IN    ELECTRO-PLATING.  679 

ease  in  liquid  ammonia  and  in  potassium  cyanide  solution. 
It  is  employed  in  the  preparation  of  baths  for  silver-plating, 
for  silvering  by  boiling,  and  in  the  pastes  for  silvering  by 
friction. 

Recognition. — By  its  solubility  in  ammonia,  pulverulent 
metallic  silver  being  separated  from  the  solution  by  dipping 
in  it  bright  ribands  of  copper. 

32.  Gold  chloride  (tercldoride  of  gold,  muriate  of  gold,  auric 
chloride). — This  salt  occurs  in  commerce  as  crystallized  gold 
chloride  of  an  orange-yellow  color,  and  as  a.  brown  crystalline 
mass  which  is  designated  as  neutral  gold  chloride,  or  as  gold 
chloride  free  from  acid,  while  the  crystallized  articles  always 
contains  acid,  and,  hence,  should  not  be  used  for  gold  baths. 
Gold   chloride  absorbs  atmospheric  moisture  and  becomes  re- 
solved into  a  liquid  of  a  tine  gold  color.     On   being  moder- 
ately heated,  yellowish-white  aurous  chloride  is  formed,  and 
on  being  subjected  to  stronger  heat,  it  is  decomposed  to  me- 
tallic gold  and  chlorine  gas.     By  mixing  its  aqueous  solution 
with  ammonia,  a  yellow-brown  powder  consisting  of  fulminat- 
ing gold  is  formed.     In  a  dry  state  this  powder  is  highly  ex- 
plosive, and,  hence,  when  precipitating  it  from  gold  chloride 
solution  for  the  preparation  of  gold  baths,  it  must  be  used 
while  still  moist. 

Recognition. — By  the  formation  of  the  precipitate  of  fulmi- 
nating gold  on  mixing  the  gold  chloride  solution  with  ammo- 
nia. Further,  by  the  precipitation  of  brown  metallic  gold 
powder  on  mixing  the  gold  chloride  solution  with  green  vitriol 
solution. 

33.  Platinic  chloride. — The  substance  usually  known  by  this 
name    is    hydroplatinic   chloride.     It    forms   red-brown,    very 
soluble — and  in  fact  deliquescent — crystals.     With  ammonium 
chloride   it   forms   platoso-ammonium    chloride.     Both   com- 
binations  are  used   in    the  preparation    of  platinum    baths. 
The  solution  of  platinic  chloride  also  serves  for  coloring  silver, 
tin,  brass  and  other  metals. 

Recognition. — By  the  formation  of  a  precipitate  of  yellow 


680  ELECTRO-DEPOSITION    OF    METALS. 

platosoammonium  chloride  on  mixing  concentrated  platinic 
chloride  solution  with  a  few  drops  of  saturated  sal  ammoniac 
solution. 

V.   Cyanides. 

34.  Potassium  cyanide  (white  prussiate  of  potash).  —  For 
electro-plating  purposes  pure  potassium  cyanide  with  98  to 
99  per  cent.,  as  well  as  that  containing  80,  70  and  60  per 
cent.,  is  used,  whilst  for  pickling  the  preparation  with  45  per 
cent,  is  employed.  For  the  preparation  of  alkaline  copper 
and  brass  baths,  as  well  as  silver  baths,  the  pure  98  to  99  per 
cent,  product  is  generally  employed.  However,  for  preparing 
gold  baths  the  60  per  cent,  article  is  mostly  preferred,  because 
the  potash  present  in  all  potassium  cyanide  varieties  with  a 
lower  content  renders  fresh  baths  more  conductive.  However, 
gold  baths  may  also  be  prepared  with  98  per  cent,  potassium 
cyanide  without  fear  of  injury  to  the  efficiency  of  the  baths, 
while,  under  ordinary  circumstances,  a  preparation  with  less 
than  98  per  cent,  may  safely  be  used  for  the  rest  of  the  baths. 
However,  when  potassium  cyanide  has  to  be  added  to  the 
baths,  as  is  from  time  to  time  necessary,  only  the  pure  pre- 
paration free  from  potash  should  be  used,  because  the  potash 
contained  in  the  inferior  qualities  gradually  thickens  the  bath 
too  much. 

No  product  is  more  important  to  the  electro-plater  than 
potassium  cyanide.  The  pure  98  to  99  per  cent,  product  is  a 
white,  transparent,  crystalline  mass,  the  crystalline  structure 
being  plainly  perceptible  upon  the  fracture.  In  a  dry  state  it 
is  odorless,  but  when  it  has  absorbed  some  moisture  it  has  a 
strong  smell  of  prussic  acid.  It  is  readily  soluble  in  water, 
and  should  be  dissolved  in  cold  water  only,  since  when  poured 
into  hot  water  it  is  partially  decomposed,  which  is  recognized 
by  the  appearance  of  an  odor  of  ammonia.  Potassium  cyanide 
solution  in  cold  water  may,  however,  be  boiled  for  a  short 
time  without  suffering  essential  decomposition.  Potassium 
cyanide  must  be  kept  in  well-closed  vessels,  since  when  ex- 


CHEMICALS    USED    IN    ELECTRO-PLATING.  681 

posed  to  the  air  it  becomes  deliquescent,  and  is  decomposed 
by  the  carbonic  acid  of  the  air,  whereby  potassium  carbonate 
is  formed  while  prussic  acid  escapes.  It  is  a  deadly  poison 
and  must  be  used  with  the  utmost  caution. 

While  pure  fused  potassium  cyanide  of  98  to  99  per  cent, 
could  formerly  be  everywhere  obtained  in  commerce,  the  pres- 
ent commercial  product  consists,  as  a  rule,  of  a  mixture  of 
potassium  cyanide  and  sodium  cyanide.  The  reason  for  this 
is  that  the  dried  yellow  prussiate  of  potash  was  formerly  fused 
by  itself,  whereby  one-third  of  its  content  of  cyanogen  was 
lost,  while,  for  the  purpose  of  fixing  this  quantity  of  cyanogen, 
it  is  now  fused  with  metallic  sodium.  The  resultant  product 
contains  78  per  cent,  potassium  cyanide  and  21  per  cent, 
sodium  cyanide. 

While  for  many  electro-plating  purposes,  this  mixture  may 
take  the  place  of  pure  potassium  cyanide,  its  use  for  some  pro- 
cesses, for  instance,  in  the  preparation  of  more  concentrated 
gold  baths,  is  connected  with  certain  drawbacks.  While  the 
double  salt — potassium-gold  cyanide — dissolves  very  readily, 
sodium-gold  cyanide  is  less  soluble  and  separates  in  the  form 
of  a  pale  yellow  powder.  Sodium-copper  cyanide  shows  a 
similar  behavior,  it  being  less  soluble  than  the  potassium 
double  salt  and  as  the  electro-motive  forces  for  decomposing 
the  potassium  and  sodium  double  salts  vary,  the  use  of  a  mix- 
ture of  potassium  cyanide  and  sodium  cyanide  is,  to  say  the 
least,  not  rational.  For  certain  purposes  the  electro-plater 
should  demand  from  his  dealer  pure  potassium  cyanide  free 
from  sodium  cyanide. 

Potassium  cyanide  with  80,  70,  60  or  45  per  cent,  forms  a 
gray-white  to  white  mass  with  a  porcelain-like  fracture.  A 
pale  gray  coloration  is  not  a  proof  of  impurities,  being  due  to 
somewhat  too  high  a  temperature  in  fusing.  These  varieties 
are  found  in  commerce  in  irregular  lumps  or  in  sticks,  the 
use  of  the  latter  offering  no  advantage.  Their  behavior  to- 
wards the  air  and  in  dissolving  is  the  same  as  that  of  the  pure 
product. 


682  ELECTRO-DEPOSITION    OF    METALS. 

Recognition. — By  the  bitter  almond  smell  of  the  solution. 
By  mixing  potassium  cyanide  solution  with  ferric  chloride  and 
then  with  hydrochloric  acid  until  the  latter  strongly  predom- 
inates., a  precipitate  of  Berlin  blue  is  formed. 

The  pure  salt  free  from  potash  does  not  effervesce  on  add- 
ing dilute  acid,  which  is,  however,  the  case  with  the  inferior 
qualities. 

To  facilitate  the  use  of  potassium  cyanide  with  a  different 
content  than  that  given  in  a  formula  for  preparing  a  bath, 
the  following  table  is  here  given  : 


Potassium  cyanide  with 


98  per  cent. 

80  per  cent. 

70  per  cent. 

60  per  cent. 

45  per  cent. 

By  weight.  By  weight.  By  weight.  By  weight.  By  weight. 

1          part  =  1. 2;  0  parts  =:  1.400  parts  -^  1.660  parts  ==  2.180  parts. 

0.820  part  ==  1         part  =  1.143  paits  =  -    1.333  parts  =-  1.780  parts. 

0.714  part  --  0.875  part  =  1         part  =   1.170  parts  -=  1.550  parts. 

0.615  part  =  0.740  part  =  0.857  part  —   1         part  •=  1.450  parts. 

0.460  part  =  0.562  part  =  0.643  part  =  0.750  part  =  1         part. 


35.  Copper  cyanide. — There  is  a  cuprous  and  a  cupric  c}Ta- 
nide  ;  that  used  for  electro-plating  purposes  being  a  mixture 
of  both.  It  is  a  green-brown  powder,  which  should  not  be 
entirely  dried,  since  in  the  moist  state  it  dissolves  with  greater 
ease  in  potassium  cyanide  than  the  dried  product. 

It  is  chiefly  used  in  the  form  of  a  double  salt  potassium- 
copper  cyanide,  i.  e.,  a  combination  of  copper  cyanide  with 
potassium  cyanide,  in  the  preparation  of  copper,  brass,  tombac, 
and  red  gold  baths. 

Recognition. — By  evaporating  a  piece  of  copper  cyanide  the 
size  of  a  pea,  or  its  solutions,  in  hydrochloric  acid,  to  dry  ness 
on  a  water-bath,  wherein  care  must  be  taken  not  to  inhale  the 
vapors,  and  dissolving  the  residue  in  water,  a  green-blue 
solution  is  obtained  which  acquires  a  deep  blue  color  by  the 
addition  of  ammonia  in  excess. 


CHEMICALS    USED    IN    ELECTRO-PLATING.  683 

36.  Zinc  cyanide  (hydrocyanate,  of  zinc,  prussiate  of  zinc). — A 
white  powder  insoluble  in  water,  but  soluble  in  potassium 
cyanide,  ammonia  and  the  alkaline  sulphites.     The  fresher  it 
is,  the  more  readily  it  dissolves,  the  dried  product  dissolving 
with    difficulty.      Its    solution    in    potassium    cyanide    forms 
potassium-zinc  cyanide,  which  is  used  for  brass  baths. 

Recognition. — By  evaporating  zinc  cyanide,  or  its  solution, 
with  an  excess  of  hydrochloric  acid  on  the  water-bath,  zinc 
chloride  remains  behind,  which  is  recognized  by  the  same  re- 
action given  under  zinc  chloride. 

37.  Silver  cyanide  (prussiate    or  hydrocyanate  of  silver). — A 
white  powder  which  slowly  becomes  black  when  exposed  to 
light.     It  is  insoluble  in  water  and  cold  acids,  which,  how- 
ever, will  dissolve  it  with  the  aid  of  heat.     At  750°  F.  it  melts 
to  a  dark  red   fluid,  which,  on  cooling,  forms  a  yellow  mass 
with  a  granular  structure.     It  is  readily  dissolved  by  potas- 
sium cyanide,  but  is  only  slightly  soluble  in  ammonia,  differ- 
ing in  this  respect  from  silver  chloride.     It  forms  a  double 
salt  with  potassium  cyanide — potassium -silver  cyanide — and 
as  such  is  employed  in  the  preparation  of  silver  baths. 

38.  Potassium  ferro-cyanide  (yellow  prussiate  of  potash). — It 
occurs   in  the  shape  of  yellow  semi-translucent  crystals  with 
mother-of-pearl  luster,  which  break  without  noise.     Exposed 
to  heat  they  effloresce,  losing  their  water  of  crystallization,  and 
crumbling  to  a  yellowish-white  powder.     For  the  solution  of 
1  part  of  the  salt,  4  of  water  of  medium  temperature  are  re- 
quired, the  solution  exhibiting  a  pale  yellow  color.     It  pre- 
cipitates nearly   all  the  metallic   salts   from   their  solutions, 
some  of  the  precipitates  being  soluble  in  an  excess  of  the  pre- 
cipitating agent.     This  salt  is  not  poisonous.     It  serves  for 
the  preparation   of  silver  and   gold   baths  ;  its  employment, 
however,    offering    over   potassium    cyanide    no    advantages, 
unless  the  non-poisonous  properties  be  considered  as  such. 

Recognition. — When  the  yellow  solution  is  mixed  with  ferric 
chloride,  a  precipitate  of  Berlin  blue  is  formed  ;  by  blue  vitriol 
solution  a  brown-red  precipitate  is  obtained. 


684  ELECTRO- DEPOSITION    OF    METALS. 

VI.   Carbonates. 

39.  Potassium  carbonate  (potash). — It  is  found  in  commerce 
in  gray-white,  bluish,  yellowish  pieces,  the  colorations  being 
due  to   admixtures   of  small   quantities  of  various  metallic 
oxides.     When  pure  it  is  in  the  form  of  a  white  powder,  or  in 
pieces  the  size  of  a  pea.     The  salt,  being  very  deliquescent, 
has  to  be  kept  in  well-closed  receptacles.     It  is  readily  soluble, 
and  if  pure,  the  solution  in  distilled  water  should  be  clear.     It 
serves  as  an  addition  to  some  baths,  and  in  an  impure  state 
for  freeing  objects  from  grease. 

Recognition. — The'  solution  effervesces  on  the  addition  of 
hydrochloric  acid.  When  neutralized  with  hydrochloric  acid 
it  gives  with  platinum  chloride  a  heavy  yellow  precipitate  of 
platinic  potassium  chloride,  provided  it  be  not  too  dilute. 

40.  Acid  potassium  carbonate  or  monopotassic  carbonate,  com- 
monly  called    bicarbonate   of   potash. — Colorless,    transparent, 
crystals,  which  at  a  medium  temperature  dissolve  to  a  clear 
solution  in  4  parts  of  water.     It  is  not  deliquescent ;  however, 
on  boiling  its  solution  it  loses  carbonic  acid,  and  contains  then 
only  potassium  carbonate.     It  is  employed  for  the  preparation 
of  certain  baths  for  gilding  by  simple  immersion. 

41.  Sodium  carbonate  (washing  soda). — It  occurs  in  commerce 
as  crystallized  or  calcined  soda  of  various  degrees  of  purity. 
The  crystallized  product  forms  colorless  crystals  or  masses  of 
crystals,   which,    on    exposure  to   air,   rapidly   effloresce  and 
crumble  to  a  white  powder.     By  heating,  the  crystals  also  lose 
their  water,  a  white  powder,  the  so-called   calcined  soda,  re- 
maining behind.     Soda  dissolves  readily  in  water,  and  serves 
as  an  addition  to  copper  and  brass  baths,  for  the  preparation 
of  metallic  carbonates,  and  for  freeing  objects  from  grease,  the 
ordinary  impure  soda  being  used  for  the  latter  purpose. 

The  directions  for  additions  of  sodium  carbonate  to  baths 
generally  refer  to  the  crystallized  salt.  If  calcined  soda  is  to 
be  used  instead,  0.4  part  of  it  will  have  to  be  taken  for  1  part 
of  the  crystallized  product. 

42.  Sodium    bicarbonate    (baking    powder). — A     dull     white 


CHEMICALS    USED    IN    ELECTRO-PLATING.  685 

powder  soluble  in  10  parts  of  water  of  68°  F.  On  boiling,  the 
solution  loses  one-half  of  its  carbonic  acid,  and  then  contains 
sodium  carbonate  only. 

43.  Calcium  carbonate  (marble,  chalk). — When  pure  it  forms 
a  snow-white  crystalline  powder,  a  yellowish  color  indicating 
a  content  of  iron.     It  is  insoluble  in  water,  but  soluble,  with 
effervescence,   in  hydrochloric,   nitric  and  acetic  acids.      In 
nature,  calcium  carbonate  occurs  as  marble,  limestone,  chalk. 

In  the  form  of  whiting  (ground  chalk  carefully  freed  from 
all  stony  matter)  it  is  used  for  the  removal  of  an  excess  of 
acid  in  acid  copper  baths,  and  mixed  with  burnt  lime,  as  an 
agent  for  freeing  objects  from  grease. 

44.  Copper  carbonate. — Occurs  in  nature  as  malachite  and 
allied    minerals.     The   artificial   carbonate  is   an    azure-blue 
substance,  insoluble  in  water,  but  soluble,  with  effervescence, 
in  acids.     Copper  carbonate  precipitated  from  copper  solution 
by  alkaline  carbonates  has  a  greenish  color.     Copper  carbonate 
is  employed  for  copper  and  brass  baths  and  for  the  removal  of 
an  excess  of  acid  in  acid  copper  baths. 

Recognition. — Dissolves  in  acids  with  effervescence  ;  on  dip- 
ping a  ribband  of  bright  sheet-iron  in  the  solution,  copper 
separates  upon  the  iron.  On  compounding  the  solution  with 
ammonia  in  excess,  a  deep  blue  coloration  is  obtained. 

45.  Zinc  carbonate. — A  white  powder,  insoluble  in  water. 
The  product  obtained  by  precipitating  a  zinc  salt  with  alka- 
line carbonate  is  a  combination  of  zinc  carbonate  with  zinc 
oxyhydrate.     It  serves  for  brass    baths  in  connection   with 
potassium  cyanide. 

Recognition. — In  a  solution  in  hydrochloric  acid,  which  is 
formed  with  effervescence,  according  to  the  reactions  given 
under  zinc  chloride  (27). 

46.  Nickel  carbonate. — A  pale  apple-green  powder,  insoluble 
in  water,  but  soluble,  with  effervescence,  in  acids.     It  is  em- 
ployed for  neutralizing  nickel  baths  which  have  become  acid. 

Recognition. — In  hydrochloric  acid,  it  dissolves,  with  effer- 
vescence, to  a  green  fluid.  By  the  addition  of  a  small  quan- 


686  ELECTRO-DEPOSITION    OF    METALS. 

tity  of  ammonia,  nickel  oxyhydrate  is  precipitated,  which,  by 
adding  ammonia  in  excess,  is  redissolved,  the  solution  showing 
a  blue  color. 

47.  Cobaltous  carbonate. — A   reddish  powder,   insoluble  in 
water,  but  soluble  in  acids,  the  solution  forming  a  red  fluid. 

VII.  Sulphates  and  sulphites. 

48.  Sodium  sulphate  (Glauber's  salt). — Clear  crystals  of  a 
slightly  bitter  taste,  which  effloresce  by  exposure  to  the  air. 
They  are  readily  soluble  in  water.     On  heating,  the  crystals 
melt  in  their  water  of  crystallization,  and  when  subjected  to  a 
red  heat,  calcined  Glauber's  salt  remains  behind.     It  is  used 
as  an  addition  to  some  baths. 

49.  Ammonium  sulphate. — It  forms  a  neutral,  colorless  salt, 
which  is  constant  in  the  air,  readily  dissolves  in  water,  and 
evaporates  on   heating.     It   serves  as  a   conducting  salt  for 
nickel,  cobalt  and  zinc  baths. 

Recognition. — By  its  evaporating  on  heating.  A  concen- 
trated solution  compounded  with  platinic  chloride  gives  a 
yellow  precipitate  of  platoso-ammonium  chloride,  while  a 
solution  mixed  with  a  few  drops  of  hydrochloric  acid  gives 
with  barium  chloride  a  precipitate  of  barium  sulphate. 

50.  Potassium-aluminium  sulphate  (potash-alum). — Colorless 
crystals  or  pieces  of  crystals  with  an  astringent  taste.     It  is 
soluble  in  water,  12  parts  of  it  dissolving  in  100  parts  of  water 
at  the  ordinary  temperature.     On  heating,  the  crystals  melt, 
and  are  converted   into  a  white,  spongy  mass,  the  so-called 
burnt  alum.     Potash-alum  serves  for  the  preparation  of  zinc 
baths  and  for  brightening  the  color  of  gold. 

Recognition. — On  adding  sodium  phosphate  to  the  solution 
of  this  salt  a  jelly-like  precipitate  of  aluminium  phosphate  is 
formed,  which  is  soluble  in  caustic  potash,  but  insoluble  in 
acetic  acid. 

51.  Ammonium-alum  is  exactly  analogous  to  the  above,  the 
potassium  sulphate  being  simply  replaced  by  ammonium  sul- 
phate.    It  is  for  most  purposes  interchangeable  with  potash- 


CHEMICALS    USED    IN    ELECTRO-PLATING.  687 

alum.  On  exposing  ammonium-alum  to  a  red  heat,  the  am- 
monium sulphate  is  lost,  pure  alumina  remaining  behind. 
Ammonium-alum  is  used  for  preparing  a  bath  for  zincking 
iron  and  steel  by  immersion. 

Recognition. — The  same  as  potash-alum.  On  heating  the 
comminuted  ammonium-alum  with  potash-lye,  an  odor  of 
ammonia  becomes  perceptible. 

52.  Ferrous  sulphate  (sulphate  of  iron,  protosulphate  of  iron, 
copperas,  green  vitriol). — Pure  ferrous  sulphate  forms  bluish- 
green,  transparent  crystals  of  a  sweetish,  astringent  taste,  which 
readily  dissolve  in  water,  and  effloresce  and  oxidize  in  the  air. 
The  crude  article  forms  green  fragments  frequently  coated 
with  a  yellow  powder.     It  generally  contains,  besides  ferrous 
sulphate,  the  sulphate  of  copper  and  of  zinc,  as  well  as  ferric 
sulphate.     Ferrous  sulphate  is  employed  in  the  preparation 
of  iron  baths,  and  for  the  reduction  of  gold  from  its  solutions. 

Recognition. — By,  compounding  the  green  solution  with  a 
few  drops  of  concentrated  nitric  acid,  a  black-blue  ring  is 
formed  on  the  point  of  contact.  On  mixing  the  lukewarm 
solution  with  gold  chloride,  gold  is  separated  as  a  brown 
powder,  which  by  rubbing  acquires  the  luster  of  gold. 

53.  Iron- ammonium   sulphate. — Green  -crystals    which    are 
constant  in  the  air  and  do  not  oxidize  as  readily  as  green 
vitriol.     100  parts  of  water  dissolve  16  parts  of  this  salt.     It 
is  used  for  the  same  purposes  as  green  vitriul. 

54.  Copper  sulphate  (cupric  sufphate,  blue  vitriol,  or  blue  cop- 
peras).— It  forms  large,  blue  crystals,  of  which  190  parts  of 
cold  water  dissolve  about  forty  parts,  and  the  same  volume  of 
hot  water  about  200  parts.     Blue  vitriol  which  does  not  pos- 
sess a  pure  blue  color  but  shows  a  greenish  luster,  is  contam- 
inated with  green  vitriol,  and  should  not  be  used  for  electro- 
plating purposes.     Blue  vitriol  serves  for  the  preparation  of 
alkaline  copper  and  brass  baths,  acid  copper  baths,  etc. 

Recognition. — By  its  appearance,  as  it  can  scarcely  be  mis- 
taken for  anything  else.  A  content  of  iron  is  recognized  by 
boiling  blue  vitriol  solution  with  a  small  quantity  of  nitric 


688  ELECTRO-DEPOSITION    OP    METALS. 

acid,  and  adding  ammonia  in  excess  ;  brown  flakes  indicate 
iron. 

55.  Zinc  sulphate  (white  vitriol). — It   forms  small  colorless 
prisms  of  a  harsh  metallic  taste,  which  readily  oxidize  on  ex- 
posure to  the  air.     By  heating  the  crystals  melt,  and  by  heat- 
ing to  a  red  heat  they  are  decomposed  into  sulphurous  acid 
and  oxygen,  which  escape,  while  zinc  oxide  remains  behind  as 
residue.     100  parts  of  water  dissolve  about  50  parts  of  zinc 
sulphate  in  the  cold,  and   nearly   100  parts  at  the  boiling- 
point.     Zinc  sulphate  is  employed  for  the  preparation  of  brass 
and  zinc  baths,  as  well  as  for  mat  pickling. 

Recognition. — By  mixing  zinc  sulphate  solution  with  acetic 
acid  and  conducting  sulphuretted  hydrogen  into  the  mixture,  a 
white  precipitate  of  zinc  sulphide  is  formed.  A  slight  content 
of  iron  is  recognized  by  the  zinc  sulphate  solution,  made  alka- 
line by  ammonia,  giving  with  ammonia  sulphide  a  somewhat 
colored  precipitate  instead  of  a  pure  white  one.  However,  a 
slight  content  of  iron  does  no  harm. 

56.  Nickel  sulphate. — Beautiful  dark  green  crystals,  readily 
soluble  in  water,  the  solution  exhibiting  a  green  color.     On 
heating  the  crystals  to  above  536°  F.,  yellow  anhydrous  nickel 
sulphate  remains  behind.     Like  the  double  salt  described  be- 
low, it  serves  for  the  preparation  of  nickel  baths  and  for  color- 
ing zinc. 

Recognition. — By  compounding  the  solution  with  ammonia 
the  green  color  passes  into  blue.  Potassium  carbonate  pre- 
cipitates pale  green  basic  nickel  carbonate,  which  dissolves  on 
adding  ammonia  in  excess,  the  solution  showing  a  blue  color. 
A  content  of  copper  is  recognized  by  the  separation  of  black- 
brown  copper  sulphide  on  introducing  sulphuretted  hydrogen 
into  a  heated  solution  previously  strongly  acidulated  with 
hydrochloric  acid. 

57.  Nickel-ammonium  sulphate. — It  forms  green  crystals  of  a 
somewhat  paler  color  than  nickel  sulphate.     This  salt  dissolves 
with  more  difficulty  than  the  preceding,  100  parts  of  water 
dissolving  only  5.5  parts  of  it.     It  is  used  for  the  same  pur- 


CHEMICALS    USED    IN    ELECTRO-PLATING.  689 

poses  as  the  nickel  sulphate,  and  is  also  recognized  in  the  same 
manner.  The  following  reaction  serves  for  distinguishing  it 
from  nickel  sulphate :  By  heating  nickel  sulphate  in  concen- 
trated solution  with  the  same  volume  of  strong  potash  or  soda 
lye,  no  odor  of  ammonia  is  perceptible,  while  nickel-ammon- 
ium sulphate  evolves  ammoniacal  gas  which  forms  dense 
clouds  on  a  glass  rod  moistened  with  hydrochloric  acid. 

58.  Cobaltous  sulphate. — Crimson  crystals  of  a  sharp  metallic 
taste.     They  are  constant  in   the  air  and  readily  dissolve  in 
water,   the  solution   showing  a   red   color.     By   heating   the 
crystals  lose  their  water  of  crystallization  without,  however, 
melting,   and  become  thereby   transparent   and   rose-colored. 
The  salt  is  used  for  cobalt  baths  for  the  electro- deposition  of 
cobalt  and  for  cobalting  by  contact. 

Recognition. — In  the  presence  of  ammoniacal  salts,  caustic 
potash  precipitates  a  blue  basic  salt,  which  on  heating  changes 
to  a  rose-colored  hydrate  and,  by  standing  for  some  time  in 
the  air,  to  a  green-brown  hydrate.  By  mixing  a  concentrated 
solution  of  the  salt  strongly  acidulated  with  hydrochloric  acid, 
with  solution  of  potassium  nitrate,  a  reddish-yellow  precipitate 
is  formed. 

59.  Cobalt-ammonium  sulphate. — This  salt  forms  crystals  of 
the  same  color  as  cobalt  sulphate,  which,  however,  dissolve 
more  readily  in  water. 

60.  Sodium   sulphite    and    bisulphite. — a.    Sodium   sulphite. 
Clear,  colorless,  and  odorless  crystals,  which  are  rapidly  trans- 
formed into  an  amorphous  powder  by  efflorescence.     The  salt 
readily  dissolves  in  water,  the  solution  showing  a  slight  alka- 
line reaction  due  to  a  small  content  of  sodium  carbonate.     It 
is  employed  in  the  preparation  of  gold,  brass,  and  copper  baths, 
for  silvering  by  immersion,  etc. 

Recognition. — The  solution  when  mixed  with  dilute  sul- 
phuric acid  has  an  odor  of  burning  sulphur. 

b.  Sodium  bisulphite. — Small  crystals,  or  more  frequently 
in  the  shape  of  a  pale  yellow  powder  with  a  strong  odor  of  sul- 
phurous acid  and  readily  soluble  in  water.  The  solution 
44 


690  ELECTRO-DEPOSITION    OF    METALS. 

shows  a  strong  acid  reaction  and  loses  sulphurous  acid  in  the 
air.  It  is  employed  in  the  preparation  of  alkaline  copper  and 
brass  baths. 

Both  the  sulphite  and  bisulphite  must  be  kept  in  well- 
closed  receptacles,  as  by  the  absorption  of  atmospheric  oxygen 
they  are  converted  to  sulphate. 

61.  Cuprous  sulphite. — A   brownish-red   crystalline  powder 
formed  by  treating  cuprous  hydrate  with  sulphurous  acid  solu- 
tion.    It  is  insoluble  in  water,  but  readily  soluble  in  potassium 
cyanide,  with  only  slight  evolution  of  cyanogen.     It  serves  for 
the  preparation  of  alkaline  copper  baths  in  place  of  basic  ace- 
tate of  copper  (verdigris),  blue  vitriol,  or  cuprous  oxide. 

VIII.    Nitrates. 

62.  Potassium  nitrate  (saltpetre,  nitre). — It  forms  large,  pris- 
matic crystals,  generally  hollow,  but  also  occurs  in  commerce 
in  the  form  of  a  coarse  powder,  soluble  in  4  parts  of  water  at  a 
medium  temperature.     The  solution  has  a  bitter,  saline  taste 
and  shows  a  neutral  reaction.     Potassium  nitrate  melts  at  a 
red  heat,  and  on  cooling  congeals  to  an  opaque,  crystalline 
mass.     It  is  employed  in  the  preparation  of  desilvering  pickle 
and  for  producing  a  mat  luster  upon  gold  and  gilding.     For 
these  purposes  it  may,  however,  be  replaced  by  the  cheaper 
sodium  nitrate,  sometimes  called  cubic  nitre  or  Chile  saltpetre. 

Recognition. — A  small  piece  of  coal  when  thrown  upon  melt- 
ing saltpetre  burns  fiercely.  When  a  not  too  dilute  solution 
of  saltpetre  is  compounded  with  solution  of  potassium  bitar- 
trate  saturated  at  the  ordinary  temperature,  a  crystalline  pre- 
cipitate of  tartar  is  formed. 

63.  Sodium  nitrate  (cubic  nitre  or  Chile  saltpetre). — Colorless 
crystals,  deliquescent  and  very  soluble  in  water ;  the  solution 
shows  a  neutral  reaction.     It  is  used  for  the  same  purposes  as 
potassium  nitrate. 

64.  Mercurous   nitrate. — It   forms   small,   colorless  crystals, 
which  are  quite  transparent  and  slightly  effloresce  in  the  air. 
On  heating,  they  melt  and  are  transformed,  with  the  evolution 


CHEMICALS    USED    IN    ELECTRO-PLATING.  691 

of  yellow-red  vapors,  into  yellow-red  mercuric  oxide,  which, 
on  further  heating,  entirely  evaporates.  With  a  small  quan- 
tity of  water,  mercurous  nitrate  yields  a  clear  solution.  By 
the  further  addition  of  water  it  shows  a  milky  turbidity, 
which,  however,  disappears  on  adding  nitric  acid.  It  is  em- 
ployed for  quicking  the  zincs  of  the  cells,  and  the  objects 
previous  to  silvering,  and  for  brightening  (with  subsequent 
heating)  gilding.  For  the  same  purpose  is  also  used  : 

65.  Mercuric  nitrate  (nitrate  of  mercury). — This  salt  is  ob- 
tained with  difficulty  in  a  crystallized  form.     It  is  generally 
sold  in  the  form  of  an  oily,  colorless  liquid  which,  in  contact 
with  water,  separates  a  basic  salt.     This  precipitate  disappears 
upon  the  addition  of  a  few  drops  of  nitric  acid,  and  the  liquid 
becomes  clear. 

Recognition. — A  bright  ribband  of  copper  dipped  in  solution 
of  mercurous  or  mercuric  nitrate  becomes  coated  with  a  white 
amalgam,  which  disappears  upon  heating. 

66.  Silver  nitrate  (lunar  caustic). — This  salt  is  found  in  com- 
merce in  three  forms :  Either  as  crystallized  nitrate  of  silver 
in  thin,  rhombic,  and  transparent  plates ;  or  in  amorphous, 
opaque,  and  white  plates  of  fused  nitrate  ;  or  in  small  cylinders 
of  a  white,  or  gray,  or  black  color,  according  to  the  nature  of 
the  mould   employed,  in  which  form  it  constitutes  the  lunar 
caustic  for  surgical  uses.     For  our  purposes  only  the  pure, 
crystallized  product,  free  from  acid,  should  be  employed.     The 
crystals  dissolve  readily  in  water.     In  making  solutions  of  this 
and  other  silver  salts,  only  distilled  water  should  be  used  ;  all 
other  waters,  owing  to  the  presence  of  chlorine,  produce  a 
cloudiness  or  even   a  distinct  precipitate  of  silver  chloride. 
When  subjected  to  heat  the  crystals  melt  to  a  colorless,  oily 
fluid,  which,  on  cooling,  congeals  to  a  crystalline  mass.     Silver 
nitrate  is  employed  in  the  preparation  of  chloride  and  cyanide 
of  silver  for  silver  baths.     The  solution  in  potassium  cyanide 
may  also  be  used  for  silver  baths.     The  alcoholic  solution  is 
employed  for  metallizing  non-conductive  moulds  for  galvan- 
oplastic  deposits. 


692  ELE<JTRO-DEPOSITION    OF    METALS. 

Recognition. — Hydrochloric  acid  and  common  salt  solution 
precipitate  from  silver  nitrate  solution  silver  chloride,  which 
becomes  black  on  exposure  to  the  light,  and  is  soluble  in  am- 
monia. 

IX.  Phosphates  and  Pyrophosphates. 

67.  Sodium  Phosphate. — Large,  clear  crystals,  which  readily 
effloresce,  and  whose  solution  in  water  shows  an  alkaline  re- 
action.    It  is  employed  in  the  preparation  of  gold  baths  and 
for  the  production  of  metallic  phosphates  for  soldering. 

Recognition. — The  dilute  solution  compounded  with  silver 
nitrate  yields  a  yellow  precipitate  of  silver  phosphate. 

68.  Sodium  pyrophosphate. — It  forms  white  crystals,  which 
are  not  subject  to  efflorescence,  and  are  soluble  in  6  parts  of 
water  at  a  medium  temperature ;  the  solution  shows  an  alka- 
line reaction.     Sodium  pyrophosphate   also  occurs  in  com- 
merce in  the  form  of  an  anhydrous  white  powder,  though  it 
may  here  be  said  that  the  directions  for  preparing  baths  refer 
to  the  crystallized  salt.     It  is  employed  in  the  preparation  of 
gold,  nickel,  bronze,  and  tin  baths. 

Recognition. — The  dilute  solution  compounded  with  silver 
nitrate  yields  a  white  instead  of  a  yellow  precipitate. 

69.  Ammonium  phosphate. — A  colorless  crystalline  powder 
quite  readily  soluble  in  water ;    the  solution  should   be  as 
neutral  as  possible.     A  salt  smelling  of  ammonia,  as  well  as 
one  showing  an  acid  reaction,  should  be  rejected.     It  is  em- 
ployed in  the  preparation  of  platinum  baths. 

X.  Salt>8  of  Organic  Acids. 

70.  Potassium   bitartrate  (cream  of  tartar). — The   pure  salt 
forms  small  transparent  crystals,  which  have  an  acid  taste, 
and  are  slightly  soluble  in  water.     The  commercial  crude 
tartar  or  argol,  which  is  a  by-product  in  the  wine-industry, 
forms  gray  or  dirty-red  crystalline  crusts.     In  a  finely  pow- 
dered state,  purified   tartar  is  called  cream  of  tartar.     It  is 
employed  for  the  preparation  of  the  whitening  silver  baths, 


CHEMICALS    USED    IN    ELECTRO-PLATING.  693 

for  those  of  tin,  and  for  the  silvering  paste  for  silvering  by 
friction,  and  in  scratch-brushing  different  deposits. 

71.  Potassium-sodium  tartrate  (Rochelle  or  Seignelte  salt). — 
Clear  colorless  crystals,  constant  in  the  air.  of  a  cooling,  bitter, 
saline  taste,  and  soluble  in  2.5  parts  of  water  of  a  medium 
temperature.     The  solution  shows  a  neutral  reaction.     This 
salt  is  employed  in  the  preparation  of  copper  baths  free  from 
cyanide,  as  well  as  of  nickel  and  cobalt  baths,  which  are  to  be 
decomposed  in  the  single  cell  apparatus. 

Recognition. — By  the  addition  of  acetic  acid  the  solution 
yields  an  abundant  precipitate  of  tartar. 

72.  Antimony-potassium    tartrate   (tartar    emetic). — A     white 
crystalline  substance,  of  which  100  parts  of  cold  water  dissolve 
5  parts,  while  a  like  volume  of  hot  water  dissolves  50  parts. 
The  solution  shows  a  slight  acid  reaction.     The  only  use  of 
this  salt  is  for  the  preparation  of  antimony  baths. 

Recognition. — The  solution  of  the  salt  compounded  with  sul- 
phuric, nitric,  or  oxalic  acid  yields  a  white  precipitate,  in- 
soluble in  an  excess  of  the  cold  acid.  Sulphuretted  hydrogen 
imparts  to  the  dilute  solution  a  red  color.  .Hydrochloric  acid 
effects  a  precipitate,  which  is  redissolved  by  the  acid  in  excess. 

73.  Copper  acetate  (verdigris). — It  is  found  in  the  market  in 
the  form  of  dark  green  crystals  showing  an   acid  reaction,  or 
as  a  neutral  bright  green  powder. 

The  crystallized  copper  acetate  forms  opaque  dark  green 
prisms,  which  readily  effloresce,  becoming  thereby  coated  with 
a  pale  green  powder.  They  dissolve  with  difficulty  in  water, 
but  readily  in  ammonia,  forming  a  solution  of  a  blue  color. 
They  dissolve  readily  also  in  potassium  cyanide  and  alkaline 
sulphites. 

The  neutral  copper  acetate  forms  a  blue-green  crystalline 
powder,  imperfectly  soluble  in  water,  but  readily  soluble  in 
ammonia,  forming  a  solution  of  a  blue  color. 

Copper  acetate  is  used  for  preparing  copper  and  brass  baths, 
for  the  production  of  artificial  patinas,  for  coloring,  gilding,  etc. 

Recognition. — On  pouring  sulphuric  acid  over  copper  ace- 


694  ELECTRO-DEPOSITION    OF    METALS. 

tate,  a  strong  odor  of  acetic  acid  is  noticed ;  with  ammonia  it 
yields  a  blue  solution. 

74.  Lead  acetate  (sugar  of  lead). — Colorless  lustrous  prisms 
or  needles  of  a  nauseous  sweet  taste,  and  poisonous.     The 
crystals  effloresce  in  the  air,  melt  at  104°  F.,  and  are  readily 
soluble  in  water,  yielding  a  slightly  turbid  solution.     Lead 
acetate  is  employed  for  preparing  lead  baths  (Nobili's  rings) 
and  for  coloring  copper  and  brass. 

Recognition. — By  compounding  lead  acetate  solution  with 
potassium  chromate  solution,  a  heavy  yellow  precipitate  of 
lead  chromate  is  formed. 

75.  Sodium  citrate. — Colorless  crystals,  presenting  a  moist 
appearance,  which  are  readily  soluble  in  water ;  the  solution 
should  show  a  neutral  reaction.     This  salt  is  employed  in  the 
preparation  of  the  platinum  bath  according  to  Bottger's  for- 
mula, and  as  conducting  salt  for  nickel  and  zinc  baths. 


APPENDIX. 


CONTENTS  OF  VESSELS. 

To  find  the  number  of  gallons  a  tank  or  other  vessel  will 
hold,  divide  the  number  of  cubic  inches  it  contains  by  231. 

If  rectangular,  multiply  together  the  length,  breadth  and 
depth. 

If  cylindrical,  multiply  the  square  of  the  diameter  by 
0.7854,  and  the  product  by  the  depth. 

If  conical,  add  together  squares  of  diameters  of  top  and 
bottom,  and  the  product  of  the  two  diameters.  Multiply  their 
sum  by  0.7854,  and  the  resulting  product  by  the  depth. 
Divide  the  product  by  3. 

If  hemispherical,  to  three  times  the  square  of  the  radius  at 
top  add  the  square  of  the  depth.  Multiply  this  sum  by  the 
depth  and  the  product  by  0.5236. 

Avoirdupois  Weight. 


=  Ounces. 

=  Drams. 

=•  Grains. 

=  Grams. 

1  Pound       .,••.. 

16 

256 

7  000 

453  25 

1  Ounc6 

1 

16 

437  5 

28.33 

1  Dram    

0.062 

1 

27.34 

1.77 

Troy   Weight. 


=  Ounces. 

=  Dwt. 

=  Grains. 

=  Grams. 

I  Pound   

12 

240 

5,760 

372.96 

1  Ounce 

1 

20 

480 

31  08 

1  Pennyweight  .... 

0.05 

1 

24 

1.55 

(695) 


696 


APPENDIX. 

Imperial  Fluid  Measure. 


1 

£ 

II 

•ii 

faO 

II 

»i 

3  £ 

EQ 

ii 

=  Minims. 

.5 

ii 
g  % 

£o 

II 

ii 

ii 

!2 

« 

J 

=  Cubic 
Centimeters. 

8 

1  60 

1280 

76  800 

Pint  

160 

g  7  qo 

?  fte° 

I-I35 

r76  fi 

Fluid  Ounce  .  .  . 
Fluid  Dram  .  .  . 

0.025 
O.OO3I 

0.05 

0.0002 

I 
0.125 

8 

i 
0.0167 

.   480 
60 

437-5 
54-7 

i-733 
0.217 

0.0284 
0.0035 

283.8 

35-5 

i  millimeter  equals 
i  centimeter      " 
I  decimeter        " 
i  meter  " 

i  cubic  centimeter  of  1 
water  equals       J 
i  liter  "  1000 


Table  of  Useful  Numerical  Data. 

.03937  inches.  |  I  troy  pound  equals 
.39370       "       !  i  avoirdupois  ounce  "> 
3.93700       "  equals  / 

39.37000       "       I  i  troy  ounce  equals 
i    avoirdupois    drm. 

equals 
i   troy  pennyweight") 


gram. 


i  liter 


Bounces  by 
measure. 


4.536 


liters. 


i  gallon  (or  1 60  fluid  "I 

ounces)  equals  / 
i  gallon  "  277.276  cubic  ins. 

i   pint  (or  20  fluid)  •„ 

ounces  equals     J 

i  fluid  ounce    "  I-733        " 

i  liter  "  61.024        " 

i  avoirdupois  pound  \ 

equals  / 


grains. 


I  gram  equals 
I  kilogram  equals 
I  liter  of  water  equals 
i  cubic  inch  of  water  ) 

equals  / 

I  cubic  centimeter  of  \ 

water  equals        > 
I  kilogram  equals 


5760.      grains. 
437-5 
480.  " 

27-34       " 

24. 

15-43   " 
15432. 
15432. 

252.5    « 


35.274  avoir- 
dupois ozs 


To  convert  Fahrenheit  thermometer  degrees  (F.)  to  Centigrade  degrees  (C),  first 
subtract  32,  then  multiply  by  5,  and  divide  by  9. 

C  =  5(F--32) 


To  convert  Centigrade  degrees  to  Fahrenheit  degrees,  multiply  by  9,  divide  by  5 
then  add  32. 


32 


APPENDIX. 


697 


H   m  O   •*  O 


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698 


APPENDIX. 


From  the  above  table  any  ordinary  conversions  up  to  2000  units  may  be  readily 
made.  For  example :  It  is  required  to  find  the  number  of  cubic  centimeters  equal 
to  1728  cubic  inches. 

1728  =  icoo  -f  700  +  20  +  8  cubic  inches. 
But  a  reference  to  the  sixth  column  shows  that 

1000  cubic  inches  =  16,385.92  cubic  centimeters. 
700          "  ~  11,470.10      "  " 

20          "  327.72      "  " 

8          "  =       131.09      "  " 


Add  together,  and  1728 


=  28,314.83      " 


Table  of  Solubilities  of  Chemical  Compounds  Commonly  L/sed  in 
Electro -Technics 


NAMES. 

Soluble  in  100  parts  by  weight  of 
water  at 

50°  F. 
Parts  by  weight. 

212°  F. 

Parts  by  weight. 

Acid    potassium    carbonate    (bicarbonate  of 

23 
400 

35 
9 
33 
73-6 
5-2 
4 
2.7 
140 

95 
very  soluble 

!33 

1  1.6 

30.5 
7-4 
soluble 

37 
61 
soluble 
very  soluble 

45-35 
48 

31-5 

6.57 
decomposable 
decomposable 

45  at  158°  F. 
very  soluble. 

1130 
422 
73 
97-5 
28  at  167°  F. 

9-5 
29 
149 
80 
very  soluble, 
very  soluble. 

43.3  at  167°  F. 
63.7  at  i58°F. 
20 
very  soluble. 
203 

333 
soluble, 
very  soluble, 
very  soluble. 
139 
71.5 
54 
decomposable, 
decomposable. 

Aluminium  sulphate  (calculated  to  anhydrous 
salt)  ,  

Ammonium  alum  

Antimony-  potassium  tartrate  (tartar  emetic)  .  . 

Cadmium  chloride  crystallized  •«  

Cadmium  sulphate  

Cobalt-ammonium  sulphate  (calculated  to  an- 

Cobalt  sulphate  (calculated  to  anhydrous  salt) 

Copper  sulphate  (blue  vitriol)  crystallized  .  .. 
Ferrous  sulphate  (green  vitriol,  copperas)..  .. 

Mercuric  chloride  (corrosive  sublimate)  

APPENDIX. 


699 


Table  oj  Solubilities  of  Chemical  Compounds  Commonly  Used  in 
Electro-  Technics. — Continued. 


Soluble  in  100  part 
water 

s  by  weight  of 
at 

NAMES. 

• 

50°  F. 
Parts  by  weight. 

212°  F. 

Parts  by  weight. 

slightly  soluble 

Nickel-ammonium  sulphate  (calculated  to  an- 

32 

28  6 

co  to  66 

Nickel    sulphate    (calculated    to    anhydrous 
salt)  

•Jly     A 

62  at  158°  F 

soluble 

c  6c 

Potassium-aluminium  sulphate  (potash  alum), 

0.05 

Q  8 

1.25 

3C7  C 

O  A 

J57-5 

6  Q 

IOQ 

o.y 
rc6 

Q/l 

XDU 

y't 

*94 

So 

O8 

Potassium  ferrocyanide  (yellow  prussiate   of 

28 

CO 

Du 

6  AC 

•^47 

<M5 

12  C 

Potassium-sodium  tartrate  (Rochelle  or  Seig- 
nette  salO                                                  • 

•^•5 

rC 

5° 

42 

7c  c 

122  at  32°  F. 

714  at  185°  F. 

227  at  67°  F. 

1  1  1  1  at  230°  F. 

Sodium  carbonate,  anhydrous  (calcined  soda) 

12 

A.O 

45 

C.4O  at  2IQ  2     F 

lf\ 

/in  i  at  7TC  ff  F 

O° 

108  c. 

167 

06  i 

1UO 

Sodium    hyposulphite,    sodium    thiosulphate 

yv.i 

6c 

^*O 

°5 

68 

•5" 

Q7 

yo 

2C 

3-5 

^J 

271 

Zinc  chloride  • 

lzb-7 

•JQQ 

343-3 

Zinc  sulphate  (white  vitriol),  crystallized.... 

JUU 
138.2 

653.6 

700  APPENDIX. 

Content  of  Metal  in  the  Most  Commonly  Used  Metallic  Salts. 


METALLIC  COMBINATION. 

FORMULA. 

!fg' 
IP 

|SJL 

Cobalt  ammonium  sulphate,  crystallized... 

(NH4)2Co(S04)2-f6H20 
CoCl2-f  6H.2O 

14.62 
24.68 

CoSO4-f  7H2O 

2(3.  Q  2 

Copper  acetate,  crystallized  (verdigris)  .  .  • 

Cu(C2H302),+  H20 
2CuCO3(CuOH)2 

31-87 

re  2O 

CuCl2-(-2H  O 

3D"*" 

37.O7 

QuCCNV-l-sHoO 

c6.co 

CuO 

70.8^ 

Copper  sulphate  (blue  vitriol),  crystallized. 

CuS04+5H.20 
Cu2O 

25.40 
88.79 

Ferrous  sulphate   (green  vitriol),  cryslal- 

FeSO  -f-  7H2O 

2O  14. 

AuClo-l-x  asf 

CQ  to  1C2 

4.8  to  4Q 

Iron-ammonium  sulphate,  crystallized...  .. 
Lead  acetate  (sugar  of  lead),  crystallized. 

(NH4)Fe(S04)2+6H20 
Pb(C8HA)2+3H20 
PbCNO  ") 

14.62 
54-57 

H0H 

7-2  87 

Hg  (NOS)2 

7Q  ^6 

Nickel-ammonium  sulphate,  crystallized... 
Nickel     carbonate,    basic     (separated    at 
212°  F)    

(NH4)2Ni(S04)2+6H20 
NiCO,4NiO,  5H2O 

14.94 
e.7.87 

NiCL-f6H»O 

:>/•"/ 

24.6^ 

NiCl2 

4^.^O 

/Ni(OH)24H2O  (separated  \ 

67  T.A. 

t                at  212°  F.)                J 
Ni(NO  )  -|-6H  O 

l8  Q7 

Ni  O 

71  OO 

Nickel  sulphate   crystallized  •• 

L^llgV/g 

NiSO  -j-7H  O 

22.OI 

Platinic  chloride  

ptCL-l-cHoO 

4C..66 

Platoso-  ammonium  chloride  

(NH  1  PtCl 

47.QI 

Potassium-copper      cyanide,     crystallized, 

K  Cu  fCN"). 

28.83 

K  Hff(CN), 

C7.C6 

"KAfrCCN") 

CA    2O 

K  Zn(CN) 

26.  •?  c 

Silver  chloride  

AoCl 

68.20 

AffCN 

80.  C  7 

AeNO0 

64.08 

SnCl  -(-  2H  O 

C.2.4C, 

NH  ZnCl,-|-2H  O 

28.98 

ZnCO,Zn(OH)2 

29.Oi; 

ZnCl2 

47.84 

Zn(CN) 

c6.C9 

Zinc  sulphate  (white  vitriol),  crystallized  .  . 

ZnSO4+7H2O 

22.73 

APPENDIX. 


701 


Table  Showing  the  Electrical  Resistance  of  Pure  Copper  Wire 
of  Various  Diameters. 


j       Number  of 

Number  of 

No.  of  wire, 
Birmingham 

Resistance  of 

feet  required 
to  give 

No.  of  wire, 
Birmingham 

feet  required 
Resistance  ol              to  give 

wire  gauge. 

i  foot  in  ohms. 

resistance 

wire  gauge. 

i  foot  in  ohms.    '      resistance 

of  i  ohm. 

of  i  ohm. 

0000 

0.0000516 

19358 

17 

O.OD3l6 

316.1 

000 

0.0000589 

16964 

18 

0.00443                 225.5 

OO 

0.0000737 

13562 

19                0.00603             l65«7 

0 

O.OOOO922 

10857 

2O                      0.00869 

1  15.1 

I 

O.OOOIlS 

8452.6 

21                       O.OIO4O 

96.2 

2 

0.000132 

7575-» 

22                        0.01358 

73-6 

3 

0.000159 

6300.1 

23                        0.01703 

58.7 

4 

0.000188 

53I9-9 

24 

O.O22OO 

45-5 

5 

O.OOO220 

4545-9 

25 

O.O266I 

37-6 

6 

0.000258 

3870-3 

26 

0.03286 

3°-4 

7 

0.000329 

3043-4 

27 

0.04159                      24.0 

8 

0.000391 

2557.1 

28 

0.05432 

18.4 

9 

0.000486 

2057.7 

29 

0.06300                      15.9 

10 

0.000593 

1686.5 

30 

0.07393                      13.5 

ii 

0.000739 

I352-5 

31 

0.10646                        9.4 

12 

0.000896 

1116.0 

32 

0.13144                        7.6 

13 

0.001180 

847-7 

33 

o.  1  6634                 6.0 

14 

0.001546 

647.0 

34 

0.21727                  4.6 

15 

0.002053 

487.0 

35 

0.42583                 2.4 

16 

0.002520 

396.8 

36 

0.66537 

'•5 

Resistance  and  Conductivity  of  Pure  Copper  at  Different 
Temperatures. 


Centigrade 
temperature. 

Resistance. 

Conductivity. 

Centigrade 
temperature. 

Resistance. 

Conductivity. 

0° 

I.OOOOO 

I.OOOOO 

1  6° 

1.06168 

.94190 

I 

1.00381 

.99624 

17 

1.06563 

.93841 

2 

1.00756 

.99250 

18 

1.06959 

•93494 

3 

I.OII35 

.98878 

19 

1-07356 

.93148 

4 

1.01515 

.98508 

20 

1.07742 

.92814 

5 

1.01896 

.98139 

21 

1.08164 

.92452 

6 

1.02280 

.97771 

22 

l-G*5S3 

.92121 

7 

1.02663 

.97406 

23 

1.08954 

.91782 

8 

1.03048 

.97042 

24 

1.09365 

.9H45 

9 

1.03435 

.96679 

25 

1.09763 

.91110 

10 

1.03822 

.96319 

26 

1.  10161 

.90776 

ii 

1.04199 

•9597° 

27 

1.10567 

.90443 

12 

1.04599 

.95603 

28 

1.11972 

.90113 

13 

1.04990 

.95247 

29 

1.11882 

.89784 

14 

1.05406 

.94893 

3° 

1.11782 

.89457 

15 

1  -°5  774 

•9454  1 

702 


APPENDIX. 


Table  of  Hydrometer  Degrees  according  to  Baume,  at  63.5°  F., 
and  their  Weights  by  volume. 


Degrees 
Be. 

Weight 
by 
volume. 

Degrees 
Be. 

Weight 
by 
volume. 

Degrees 
Be. 

Weight 
by 
volume. 

Degrees 
Be. 

Weight 
by 
volume. 

o 

i.  0600 

19 

.1487 

38 

1-3494 

57 

1.6349 

i 

1.0068 

20 

.1578 

39 

1.3619 

58 

1.6533 

2 

1.0138 

21 

.1670 

40 

L3746 

59 

1.6721 

3 

1.0208 

22 

.1763 

4i 

1.3876 

60 

1.6914 

4 

1.0280 

23 

.1858 

42 

1.4009 

61 

1.7111 

5 

1-0353 

24 

•1955 

43 

MH3 

62 

L73I3 

6 

1.0426 

25 

.2053 

44 

1.4281 

63 

1.7520 

7 

1.0501 

26 

•2153 

45 

1.4421 

64 

L773I 

8 

1.0576 

27 

.2254 

46 

1.4564 

65 

1.7948 

9 

1.0653 

28 

•2357 

47 

1.4710 

66 

1.8171 

10 

1.0731 

29 

.2462 

48 

1.4860 

67 

1.8398 

n 

1.0810 

3° 

.2569 

49 

1.5012 

68 

1.8632 

12 

1.0890 

3i 

.2677 

50 

1.5167 

69 

1.8871 

13 

1.0972 

32 

.2788 

5i 

L5325 

70 

1.9117 

H 

1.1054 

33' 

.2901 

52 

1.5487 

71 

1-937° 

1.1138 

34 

•3015 

53 

1.5652 

72 

1.9629 

16 

1.1224 

35 

•3131 

54 

1.5820 

17 

1.1310 

36 

.3250 

55 

1-5993 

18 

1.1398 

37 

1-3370 

56 

1.6169 

Table  of  Bare  Copper  Wire  for  Low  Voltage. 


1 

i 

i 

to 

S 

<u 

ill 

!-s 

ti 

S 

OS 

£  ^  J 

•s  § 

» 

5 

rc'" 

*H 

0000 

.460" 

300 

63  Ibs. 

000 

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245 

50 

00 

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2IS 

40 

o 

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190 

31 

I 

.290" 

160 

25 

2 

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J0(- 

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115 

16 

i* 

1 

£ 

Sa 

§1  . 

i 

£ 

frll 

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si. 

L8I 

2 

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rt 

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pa 

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IOO 

13     Ibs. 

.2624 

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80 

8 

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8 

10 

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.100" 

60 

4° 

S 
3 

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1.0662 

1218 

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30 

2 

1.706 

1550 

14 

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22 

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2843 

2007 

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4.264 

INDEX. 


A  CCUMUL  ATOK,  chemical  processes 
A.         in  the,  112-116 

common  form  of,  116 

performance  of,  185 
Accumulators,  111-118 

coupling  of,  118 

installation  and,  184-187 

maintenance  of,  116-118 
Acid  copper  baths,  examination  of,  594- 
596 

free,  in  acid  copper  baths,  deter- 
mination of,  594 

potassium  carbonate,  684 

pump,  233 

regaining  of,  from  dipping  baths, 
227,  228 

residue,  54 

salt,  45,  46 

vapors,  absorbing  plant  for,  227 
Acids,  40,  41,  669-673 

formation  of  salts  from,  44 
Albert,  Dr.  E.,  on  metal  matrices,  603- 

605 

Alexander's  patents,  458,  459 
Alkalies  and  alkaline  earths,  673,  674 

poisoning  by,  557 

Alliance  magnetic-electrical  machine,  7 
Alloys,  metallic,  for  moulds,  636,  637 
Alternating  actions,  electro-magnetic,  18 

currents,  generation  of,  98 
Aluminium-bronze  baths,  359 

deposition  of,  483,  484 

upon,  484-486 
Amalgamating  articles  to  be  silvered, 

382,  383 

Amalgamation,  71,  72 
Amalgams  of  potassium  and  sodium,  4 
Ammeter,  144-147 
Ammonium,  673,  674 

alum.  686,  687 

chloride,  676 

hydrate,  673,  674 

phosphate,  692 

sulphate,  6S6 

sulphide,  675 
Ampere,  20 


hour,    electro-chemical   equivalent 


of,  126 


Ampere  turn  number,  13 
Ampere's  rule,  11 

theory,  10,  11 

Analytical  chemical  process,  32 
Anions,  47 

Anode,  definition  of,  47 
Anodes,  arrangement  of,  in  the  bath, 
158-161 

brass,  355 

choice  of,  242,  243 

copper.  336 

elliptic,  268-270 

faulty  arrangement  of,  281,  282 

for  galvanoplastic  baths,  586,  587 

gas-carbon,  272 

gold,  421-424 

insoluble,  271,  272 

in  silver  baths,  372 

lead,  472,  473 

nickel,  268-275 

platinum,  271,  272 

retort-carbon,  271 

zinc,  463-465 
Antimony  baths,  478,  479 

deposition  of,  478,  479,  515 

potassium  tartrate,  693 

properties  of,  478 

sulphide,  675 

trichloride,  676 
Antique  silvering,  405 
Aqua  fortis,  670 
Areas  silver-plating,  380,  381 
Argentiferous  paste,  504,  505 
Armature,  95,  97-100 
Arrhenius,  investigation  of,  51,  52 
Arsenic,  672 

baths,  479-483 

deposition  of,  479-482,  515 

properties  of,  479 

sulphide,  675,  676 
Arsenious  acid,  672 

chloride,  677 

sulphide,  675,  676 
Astatic  galvanometer,  12 
Atomic  weights,  34,  35 
Atoms,  33,  34 
Avogrado's  law,  51 


Avoirdupois  weight,  695 

(703) 


704 


INDEX. 


Auric  chloride,  679 
Autotypes,  bath  for,  590 

BABY  shoes,  coppering,  656 
Bacco's  coppering  bath.  495,  496 
Backing  deposit  or  shell,  617,  618 

metal,  618 

Baking  powder,  684,  685 
Balance,  voltametric,  391-394 
Balances,  metallornetric,  388-391 
Barium  cyanide,  calculation  of  quantitv 

of,  410,  411 
Bases,  41 

Basse  and  Selve's  patent,  492,  493 
Bath,  arrangement  of  objects  and  anodes 

in,  158-161 
determination  of  current-output  of 

a,  127,  128 
electro-cleaning,  arrangement  of  a, 

230,  231 

general  qualifications  of  a,  246 
Baths,  233-246 

agitation  of,  236-240 
boiling  of,  240,  241 
concentration  of.  235,  236 
current-densities  and  electro-motive 

forces  required  for,  168,  169 
distinction  between,  245 
dynamo  for  series  coupling  of,  171 
effect  of  current-density  on,  244,  245 
filtering  of,  242 
galvanoplastic,  agitation  of,  581 -586 

coupling,  570-573 
glycerin  in  place  of  water  for  pre- 
paring, 251 ,  252 
prevention  of  impurities  in,  242 
reaction  of,  245,  246 
temperature  of,  236,  240 
working  of,  with  the  current,  241, 

242 

Batteries,  plunge,  84-87 
Battery,  galvanic  or  voltaic,  31 

galvanoplastic  deposition  with,  567, 

568 
Baume   hydrometer  degrees  and  their 

weights  by  volume,  702 
Belt-attachment  combined  with  double 

grinding  lathe,  202 
strapping  attachment,  212 
Bertrand's  palladium  bath,  449 
Bicarbonate  of  potash ,  684 
Bichromate  cell,  87 
Bicycle  frames,   removing  hard  solder 

from,  221,  222 
parts,  nickeling  of.  277 
Bird,  production  of  amalgams  of  potas- 
sium and  sodium  by,  4 
Bivalent  and  trivalent  elements,  38 


Bivalent  elements,  38 
Black  lacquers,,  spray  ing,  551-553 
leading  machines,  610-613 
nickeling,  260-262 
sulphide  of  antimony,  675 
Blassett,  E. ,  Jr. ,  arsenic  baths  given  by, 

481,  482 

Blue  copperas,  687,  688 
vitriol,  687,  688 

solution,  electrolysis  of,  56 
Bobs,  cloth,  207 

construction  of,  299 
Boiling  baths,  240,  241 
Boettger's  discoveries,  6,  7 

iron  bath.  476 
Boric  acid,  671,  672 

addition   of,   to   nickel  bathsr 

250,  251 

Boudreaux  brushes,  102 
Bower-Barff.  dead  black  lacquer  as  sub- 
stitute for,  547,  548 
I  Bowls,    galvanoplastic    decorations  on, 

651-656 
Branch  conductors,  153 

wires,  26 
Brandley's  method  of  making  gelatine 

moulds,  645 
Brass  anodes,  355 
baths,  349-354 

examination  of,  360-362 
tanks  for,  355 

bedsteads,  lacquering,  545,  546 
black  on,  526,  527 
brown  on,  528.  529 
castings,  grinding  of,  206 
color  resembling  gold  on,  527,  528 
coloring  of,  525-531 
cornflower-blue  on,  529,  530 
dead  red  on,  529 
deposition  of,  348-362 
deposits,  polishing  of,  216 
Ebermayer's  experiments  in  color- 
ing, 5bO,  531 
etching,  630 
gold  color  on,  527 
nieling  upon,  404,  405 
patina  for,  524 
objects,  cleaning  of,  232,  233 

pickling  of,  223,  224 
salts,  prepared,  354,  355 
scratch-brushes  for,  214 
sheet,  brushing  of.  206 

nickeling,  306 
silver  color  on   527 
steel-gray  on,  527 
straw-color,     to    brown,     through 
golden  yellow,  and  tombac  color 
on,  527 


INDEX. 


705 


Brass,  tin  bath  for,  451,  452 
tinning  solution  for,  513 
varieties  of.  348 
various  colors  on,  525 
violet  on,  52:),  5hO 
zincking.  514 
Brassed   castings,  prevention   of  stains 

on,  337 
Brassing  by  contact.  498,  499 

execution  of.  3">o-3t;0 
Bright  dipping  bath.  223 

plating,  preparations  for,  377-379 
Platinum    Plating    Co.,    platinum 

bath  of.  445 
Britannia,  cleaning  of.  233 

direct  silvering  of,  401,  402 
Bronze  Barbed ienne,  528,  529 
baths.  3li3,  3(54 

clay  yellow  to  dark  brown  on,  529 
dead  yellow  on,  529 
deposition  on.  363.  364 
objects,  cleaning  of  232,  233 

pickling  of.  223.  224 
Browning  gun  barrels,  53-J 
Brugnatelli.    first    practical    results    in 

electro-gilding  attained  by.  3 
Brush  brass  dip  lacquer  and  brush  brass 

thinner,  5-15 
finish  lacquers.  544 
-coppering.  497,  4'J8 
-holders.  102 
-rocker,  102 
Brushes,  100,  101.  192 
Buck,  J.,  patent  of.  384 
Buffing  lathes,  electrically  driven,  211 
Bunsen  cell.  75-81 

process  which    takes   place   in 

the.  76 

treatment  of.  80.  81 

Burgess,     experiments     by,     regarding 
zincking  by  the  hot  process  and 
electro-deposition,  -155-458 
on  removing  hard  solder  from  bi- 
cycle frames.  221,  2_2 
and  Harnbuechen.  process  of  plat- 
ing aluminium  by,  485,  486 
Burnishing.  213,  216,  217 
Burnt  nickeling,  278,  279 
Busts,  coppering.  650 

galvanic  reproduction  of,  634-645 
Butter  of  antimony,  676 
of  zinc,  677 

/CADMIUM  silver  bath,  380,  381 
Vy     Calcium  carbonate,  685 

hydrate,  674 
Candelabras,  coppering,  656,  657 

45 


Cane  handles,  celluloid,  galvanoplastic 

decorations  on.  056 
Carbon,  artificial,  preparation  of,  75 
blocks,  coppering,  656 
disulphide,  (575 

addition  of,  to  nickel  baths,  263 
of,  to  silver  baths,  377-379 
pins,  coppering,  656 
Carbonates,  684-<  86 
Cast  iron,  pickling  of,  218-220 
rolls,  coppering.  656 
tanks,  enameled,  154 
tin  bath  for.  451,  452 
Castings,  pickled,  dip  lacquer  for,  542, 

513 
Cathode,  definition  of.  47 

separation  of  metal  on,  56,  57 
Cations,  47 
Caustic  potash,  673 
soda.  (i73 

electrolysis  of.  55,  56 
Cell  apparatus,  copper  bath  for.  564,  565 
galvanoplastic    deposition    in, 

561-5fi6 

galvanic  or  voltaic,  31 
Cells,  coupling.  87-90.  132-135 

for    galvanoplastic    deposition    by 

battery,  o67 
forms  of,  561-563 
installations  with.  132-164 
secondary,   111-118 
voltaic,  70-84 
Celluloid  umbrella  and   cane  handles, 

galvanoplastic  decorations  on.  (i56 
Centigrade    degrees    of    thermometer, 
conversion  of  to  Fahrenheit  degrees, 
696 

Centrifugal  dryer,  164 
Chalk,  685 

Chemical  compounds,  table  of  solubili- 
ties of,  69S,  699 
elements.  33 

energy  of,  53,  54 

symbols  of.  34 

table  of  the  atomic  weights  of 

the  most  important,  35 
valence  of.  36-38 
formulas,  35,  36 
principles,  fundamental,  31-46 
processes.  32 

in  the  accumulator,  112-116 
treatment  of  objects,  218-233 
Chemicals,  poisoning  by,  556,  557 
purity  of,  234,  235 
used  in  electroplating  and  galvano- 

plasty,  669-694 
Chile  saltpetre.  690 
China,  silver  deposit  on,  652-656 


706 


INDEX. 


Chloride  of  zinc  and  ammonia,  678 
Chlorine  combinations.  676-680 

-ions,  properties  of,  48 

poisoning  by,  557 

Christofle  &  Co.,  early  use  of  magnetic- 
electrical  machines  by,  7 
Chrome  gelatine,  626,  627 
Chromic  acid.  672 
Circuit,  closed,  80 
Citric  acid,  671 

Clamond's  thermo-electric  pile,  91,  92 
Classen's  patent,  461 
Clausius,  theory  of,  nO 
Clay  objects,  coppering.  650 
Cleaning  and  rinsing  apparatus,   161- 
164 

electro-chemical,  229-231 

polished  objects,  217.  218 
Cliches,  nickeling.  312-314 
Clock  cases,  mat  black  coating  on,  535 

gilding,  bath  for,  418,  419 
Closed  circuit.  HO 
Cloth  bobs,  207 
Cobalt-ammonium  sulphate,  689 

baths,  323.  324 

deposition  of,  323-325 

properties  of,  323 
Cobalting  by  contact  and  boiling,  494, 

495 
Cobaltous  carbonate,  686 

chloride,  678 

sulphate,  689 

Coefficient  of  temperature,  26 
Coehn  and  Siemens,  investigations  by, 

268 
Coffee  sets,  galvanoplastic  decorations 

on,  651 

Colcothar,  212 

Cold  silvering  with  paste,  504,  505 
Coloring  metals.  516-537 
Commutator,  100.  101 
Compound-wound  dynamos,  105 
Concentration  of  baths,  235,  236 
Conducting  fixtures,  157,  1£8 

salts,  249,  250 
Conductors,  29.  46.  152-154 
Connection   of  main  and   branch   con- 
ductors, 154 
Conservation  of  force  and  work,  53 

matter,  law  of,  33,  53 
Contact,  deposition  by,  487-491 

-electricity,  29-31 
discovery  of,  1,  2 

metals,  489 
Contacts,  153 
Copper  acetate,  693,  694 

alloys,  nickel  bath  for,  258,  259, 
260,  262 


Copper  anodes,  336 

bath  for  incrusting  galvarioplasty, 

649 
baths,  326-333 

acid,  examination  of,  594-596 
containing  potassium  cyanide, 

examination  of,  342-348 
determination    of    copper    in, 

345-348 
of  potassium   cyanide   in, 

343-345 

galvanoplastic,  564,  565,  574, 
"  575,  586 
without     potassium     cyanide. 

334.335 

black  on,  521,  522 
blue-black  on,  520 
brass  and  bronze,  deposition  of, 

326-364 

bronzing  of,  519 
brown  on,  518,  519 

layer  of  cuprous  oxide  on,  518 
of  various  shades  on,  518,  519 
carbonate,  685 
castings,  grinding  of,  206 
chloride,  677 
cleaning  of.  232,  233 
coloring,  517-525 
cyanide,  682 

baths.  327-334 

preparation  of,  327 
tanks  for,  335,  336 
thickening  of,  341 
dark  brown  to  black  on,  520 
deposited,  properties  of,  575 
deposition  of,  326-348 
deposits,  brittle.  578,  579 

from  metallic  surfaces,  620-622 
polishing  of,  216 
determination    of,    in    brass  baths, 

360, 361 

of,  in  copper  baths,  345-348 
galvanoplasty  in,  559-657 
gold  yellow  on,  519 
in  acid  copper  baths,  determination 

of,  594,  595 

nickel  bath  for,  258,  259,  260 
patina  for,  524 
pickling  of,  223,  224 
plates,  etching.  630 
properties  of,  326 
pure,  resistance   and   conductivity 

of,  701 
quantity  of,  liberated  from  cupric 

salts,  60 

red  to  violet  shades  on,  521 
salts,  poisoning  by,  556,  567 
scratch-brushes  for,  214 


INDEX. 


707 


Copper  sheet,  brushing  of,  206 

nickeling,  306 
steel-gray  on,  524,  525 
sulphate,  687,  688 
tin  bath  for,  451,  452 
tinning  solution  for,  513 
tubes,  production  of,  646 
various  colors  on,  525 
wire,   bare,   for  low  voltage,   table 

of,  702 

pure,  table  of  electrical  resist- 
ance of,  701 
silvering,  403 
yellowish  brown  on,  519 
zinc  alloy,  solution  for  transferring 

any,  354 
zincking,  514 
Copperas,  687,  688 

Coppered  art  castings,   inlaying  of  de- 
pressions of,  341,  342 
castings,    prevention   of  stains  on, 

337 
objects,    coating   of,    with    another 

metal,  340 

Coppering  by  contact  and  dipping,  495- 
'    498 

execution  of,  336-342 
Knight's  process  of,  591 
salts,  prepared,  333,  334 
small  articles  in  quantities,  341 
stereotypes,  622,  623 
zinc  plates,  623 
Corvin's  niello,  646,  647 
Coulomb,  20 
Counter-current,  appearance  of.  66,  67 

-force,  53 

Coupling  accumulators,  118 
cells,  87-90,  1*2-135 
main  object  wire  and  main   anode 
wire,  together  with  the  resistance 
boards,    voltmeter,    switch    and 
two  baths,  148-151 
Covering  ground,  624 
Cream  of  tartar.  692,  693 
Cruikshank,  investigations  by,  3 

trough  battery  devised  by,  2,  71 
Cubic  nitre,  690 
Cuivre  fume,  520,  521 
Cupric  oxide  cell,  82,  83 

salts,  quantity  of  copper,  liberated 

from,  60 
sulphate,  687,  688 

solution,  electrolysis  of,  56 
Cupro-cupric  sulphite,  332 
Cupron  cell,  83,  84 
Cuprous  cyanide,  336 

oxide,  regeneration  of,  83 
sulphite,  690 


Cups,  gilding  inner  surfaces  of,  428 
Current,  branching  or  distributing  the, 

26 
conditions  for  galvanoplastic  baths, 

576-578 

coupling  cells  for  quantity  of,  89 
-density,  124-130 

calculation  of  quantity  by 
weight  of  deposit  from,  125, 
126 

dependence     of,     on     electro- 
motive force,  151,  152 
effect  of  in  baths.  244,  245 

nickel  baths,  252 
for  nickeling,  279-281 
-distribution,   two   and    three-wire 

systems  of,  179.  180 
electro-motive  force  of,  20,  21 
in  a  Daniell  cell,  64,  65 
-indicator,  139-141 
-lines,  scattering  of,  132,  275 
osmotic  theory  of  the   production 

of,  63-65 
-output,  245 

of  a   bath,    determination   of, 

127,  128 
preparation  of  gold  baths  with  the 

assistance  of,  420,  4zl 
primary,  inducing  or  main,  16 
-regulation,  135-139 
secondary,  induced,  or  induction, 

16 

sources  of,  70-118 
-strength,  calculation  of,  126,  127 
calculation  of  weight  of  silver 

deposit  from,  398-400 
unit  of,  20 

working  baths  with,  241.  242 
Currents,  alternating,  generation  of,  98 
( Cyanide  combinations,  poisoning  by,  556 
Cyanides.  680-684 

metallic,  first  use  of  solutions  of, 
in  potassium  cyanide,  6 

DANEEL  on  changes  in  concentration 
of  baths,  238,  239 
Daniell  cell,  73,  74 

current  in  a,  64,  65 

process  which  takes  place  in 

the,  73,  74 
Darlay's  patented  baths,  493,  494,  496, 

497,498,  499,500,512,514 
Davy,  Sir  Humphry,  discovery  of  the 

metals  sodium  and  potassium  by,  3 
Dead  black  lacquers,  546-548 
Decomposition-pressure,  67,  68 
Deposit,  absorption  of,  243 
backing,  617,  618 


708 


INDEX. 


Deposit,  detaching  the,  from  the  mould 

615-H17 

formation  of.  213,  214 
Deposition  by  contact,  487-491 

by    boiling,    and    by 

friction,  487 

galvanoplastic,  duration  of,  579,  580 
of  aluminium,  483,  484 
antimony,  478,  479 
arsenic.  479-482 
brass,  348-862 
bronze.  363,  3B4 
cobalt,  323-325 
copper.  K26-348 
iron,  475-477 
lead,  472-175 
nickel,  247-323 
palladium,  448,  449 
plaiinu'»>,  444-448 
silver,  365-414 
tin,  450-453 
tombac,  362,  363 
zinc,  4.-. 3-472 
upon  aluminium,  484-486 
Deposits,  high  luster  on,  216,  217 
scratch-brushing  of,  213-215 
De  Ruolz.    first  deposition  of  metallic 

alloys  by.  7 
DittfFenbach    and    Limpricht's    patent, 

646 

Difference  of  potential,  21 
Dip  lacquer  for  pickled  castings  to  be 

copper-plated  or  oxidized,  542,  543 
Dipping  and  pickling,  218-228 
baskets,  294 
baths,    regaining   acid   from,    227, 

228 

Direct  acting  dynamos,  103-108 
Dissociation,  electrolytic.  50-52 
Donath's  patinizing  fluids.  523 
Drum  armature,  97,  98,  99 
Drying,  215,  216 

barrel,  steam,  164 
Du  Fresne's  process  of  gilding,  433 
Dust,  devices  for   keeping  the,  out  of 

polishing  room,  123 

Dynamo  and  accumulators,  combined 
operation  with,  in  galvanoplasty, 
573 

choice  of  a,  167-172 
electric  machines.  93-111 

fundamental     principles 

of,  94.  95 

impetus  given  by,  to  the 
electro-plating  indus- 
try, 8 

installations  with,  164- 
183 


Dynamo     electric     machines,    separate 
parts  of,  96-103 

galvanoplastic  deposition  with,  568- 
573 

impressed  electro-motive  force  of, 
168,  169 

setting  up  and  running  a,  164-167 
Dynamos,  direct  acting,  103-108 

parallel  coupling  and  series  coup- 
ling of,  172-175 

EBERMAYER'S  experiments  in  col- 
oring brass,  5HO,  531 
silver  immersion  bath,  503 
Eichstaedt,  T.  C.,  on  keeping  dust  out 

of  polishing  rooms,  123 
Egyptian  Lacquer  Manufacturing  Co., 
lacquers  made  by,  542,  543,  545,  548, 
554 
Elb's  theory  of  the  chemical  processes 

in  the  accumulator,  112-115 
Electric  current,  comparison  of,  with  a 

current  of  water,  19,  20 
induction,  discovery  of,  4 
resistance  of  pure  copper  wire,  table 

of,  701 
unit  of,  22 
units,  28  24 
work,  unit  of,  21 
Electricity,  contact,  29-31 

discovery  of,  1,  2 
frictional.  28,  29 
kinds  of.  29 

unit  of  the  quantity  of,  20 
Electro-chemical  cleaning,  229-231 
equivalent,  i>0,  61 
means,  matting  by,  434,  435 
-chemistry,  fundamental  principles 

of,  4H-69 
-deposition,  production  of  colors  on 

metals  by.  536,  537 
-engraving.  631-634 
-etching.  628-625 
-magnetic  alternating  actions,  18 

induction  machine,  first,  4 
-magnetism,  11-15 
-magnets,  12 
-metallurgy,  first  application  of  the 

term,  6 

historical  review  of,  1-8 
-motive  counter-force  of  polariza- 
tion, 130-132 

force,  coupling  cells  for,  89 
dependence  of  current-den- 
sity on,  151.  152 
difference  of,  21 
for  nickel  baths,  252 
in  cell-apparatus,  566 


INDEX. 


709 


Electro-motive  force  of  current,  20,  21 
series  of,  HO 
unit  of,  21 
-plating      apparatus,     mechanical, 

295-298 
arrangements     in     particular. 

124-132 

chemicals  used  in,  669-694 
mechanical    treatment   during 

and  after,  213-218 
treatment      previous      to, 

188-213 

plant,  actual  parts  of  a,  124 
arrangement  of,  in  general, 

119-187 
with  dynamos,  ground  plans 

of,  175-180 
process,  wrong  ideas  of,  188, 

189 

solutions,  233-246 
-silvering,  special  applications  of, 

403-405 
-technics,    fundamental    principles 

of,  18-28 

table  of  solubilities  of  chemical 
compounds,  used  in,  698,  699 
Electrochroma,  536,  537 
Electrochrorny.  473-475 
Electrodes,  definition  of,  47 
processes  on  the,  54-58 
Electrolysis,  definition  of,  47 

determination  of  copper  in  copper 

baths  by,  345.  346 
of  zinc  in  brass  baths  by,  361 
Electrolyte,  electrolysis  of  a,  between 

insoluble  electrodes,  66 
resistance  of,  128-130 
Electrolytes,  46,  47,  283-246 
Electrolytic  analysis,  319-323 
dissociation,  50-52 
pickling,  220,  221 
Electrotypes,  duration  of  deposition  for, 

580 

finishing,  618-620 
iron,  657-661 
nickel,  661-664 
Electrotypy,  561-634 
Elements,  chemical,  33 

energy  of,  53,  54 
symbols  of,  34,  36 
table     of     the     atomic 

weights  of  the,  35 
valence  of,  36-38 
Elmore's  process  of  producing  copper 

tubes,  646 
Eisner's  bronze  bath,  363 

tinning  bath,  513 
Emery,  kinds  of,  198 


Enclosure  work,  interior,    lacquer   for, 

541,  542 

Endless  belt  machine,  212 
Energy,  52-54 
Etching  ground,  624 

FAHRENHEIT  degrees  of  thermom- 
eter, conversion  of,  to  Centigrade 
degrees,  696 
Faraday,  electric   induction  discovered 

by,  4 

investigations  of,  59 
laws  of,  58-60 
Feelers,  613 

Fein's  plunge  battery,  85 
Ferric  oxide,  212 
sulphide,  676 
Ferrous  sulphate,  687 
Field,  magnetic,  11.  13 
magnets,  96 
winding,  96 
Filtering  baths,  242 
Fire     gilding,    combination     of,    with 

electro-deposition,  433 
Fischer's    method   of    making  impres- 
sions, 609 
Fleming's  hand  rule,  18 
Floors  of  plating  rooms,  121,  ll}2 
Flowers,  coppering,  650 
Fluid,  evaporation  of  a,  61 
measure,  imperial,  696 
Foerster,  experiments  of,  267 

and    Seidel  on  mechanical  proper- 
ties of  deposited  copper,  575 
Force,  53 

and  work,  conservation  of,  53 
Foreign  excitation,  97 
Forks,  calculation  of  time  for  deposi- 
tion of  determined  weight  on,  127 
extra  heavy  coating  of  silver  on, 

383,  384 

Four-polar  dynamo,  96 
French  form  of  cell  apparatus,  562,  563 
Frictional  electricity.  28,  29 
Frosting  silver.  400,  401 

GAIFFE'S  cobalt  solution,  323,  324 
Galvani,  discoverv  of  contact-elec- 
tricity by,  1,  2 
Galvanic  cell    31 
current,  31 
reproduction  of  plastic  objects,  634- 

645 
Galvanometer,    indications    made    by, 

142-144 

Galvanometers,  12,  139,  140 
Galvanoplastic     baths,     agitation     of, 
581-586 


710 


INDEX. 


Gal vano plastic  baths,  current  conditions 

for,  578 
deposition  by  battery  and  dynamo, 

566-573 

duration  of,  579,  580 
in  the  cell-apparatus,  561-566 
method  for  originals  in  high  relief. 

643,  644 

process,  discovery  of,  5 
reproduction  for  graphic  purposes, 

561-634 
Galvanoplasty,  558-668 

chemicals  used  in,  669-694 

for  graphic  purposes,  operations  in, 

596-645 

in  copper,  559-657 
iron  (steel),  657-661 
nickel,  661-667 
silver  and  gold,  667,  668 
incrusting,  647-649 
rapid,  baths  for,  590,  592 
special  applications  of,  645-657 
Galvanoscopes,  12 
Gas-carbon  anodes,  272 
Gases,  solutions  of,  48 
Gassiot's  process  for  obtaining  metallo- 

chromes,  474,  475 
Gauduin's  copper  bath,  335 
Gauze,  gilding  of,  437-440 
Gelatine  moulds,  644,  645 
German  form  of  cell  apparatus,  563 

silver,  direct  silvering  of,  401.  402 
objects,  cleaning  of,  232,  233 

pickling  of,  223,  224 
sheets,  brushing  of,  206 
Gilded  articles,   stripping    gold   from, 

440,  441 

Gilder's  wax,  436 
Gilding  by  contact,  by  immersion,  and 

by  friction,  508-511 
coloring  of,  435-437 
combination    of    fire-gilding    with 

electro-deposition,  433 
genuine,  determination  of,  441 
green,  431,  432 
improving  bad  tones  of,  437 
inner  surfaces  of  hollow-ware,  428 
mat,  434,  435 

metallic  wire  and  gauze,  437-440 
red,  430,  431 

reddish,  by  friction,  510.  511 
rose  color,  432 
without  a  battery.  426 
Girders,  wrought  iron,  zincking  of,  468, 

469 
Glass,   galvanoplastic    decorations    on, 

651-656 
silver  deposit  on,  652-656 


Glauber's  salt,  686 

Glycerin,  preparation  of  baths  with,  233 

substitution  of,  for  water,  251,  252 

Gold  and  silver,  galvanoplasty  in,  667, 

668 

anodes,  421-424 
baths,  416-421 

examination  of,  441,  442 
heating,  425 
management  of,  421-424 
recovery  of  gold  from,  442, 443 
tanks  for,  424-426 
chloride,  679 
deposition  of,  415-443 
deposits,  burnishing  of,  216,  217 

polishing,  429 

estimating  the  fineness  of.  415,  41& 
incrustations  with,  403,  404 
old,  432,  433 

plating,  execution  of,  426-430 
properties  of,  415,  416 
recovery  of,  from  gold  baths,  442r 

443 
stripping  from  gilded  articles,  440r 

441 

Goldberg's  patent,  461 
Gore's  antimony  bath,  479,  480 
brass  bath,  353,  354 
process  for  silvering,  402 
Gottig's  process  of  plating  aluminium, 

486 

Gountier's  bronze  bath,  363 
Graining,  505-508 
Gramme-equivalent,  (r'O 
Gramme's  machine,  introduction  of,  8 
Graphic  purposes,  galvanoplastic  repro- 
duction for,  561-634 
operations  in  galvanoplasty 

for,  596-645 
Grasses,  coppering,  650 
Gray,  discoveries  of,  29 
Grease,  removal  of,  228,  229 
Green  gilding,  431,  432 

vitriol,  687 
Grille  work,  interior,  lacquer  for,  541, 

542 
Grinding,  196-199 

and  brushing,  execution  of,  204-206- 

polishing  rooms,  122,  123 
lathes,  200-204 

motors,  electrically  driven,  202-204 
wheels,  196-199 

removing  emery  and  glue  from. 

199,  200 

treatment  of,  199,  200 
Group  coupling,  89 
Giilcher's  thermo-electric  pile,  92,  93 
Gun  barrels,  browning,  533 


INDEX. 


711 


Gutta-percha,  introduction  of,  6 
lacquer,  640 
moulding  in,  597 

with,  636 
moulds,      detaching      deposit 

from,  615,  616 
electrical  contact  of,  613 

HABER'S  proposition,  257 
Haen's  method  of  determination 
of  content   of  copper  in   acid 
copper  bath .  594,  595 
Haloid  acids,  41 
Hand  rule,  Fleming's,  18 
Hansjosten,  J.  H. ,  on  pickling  cast  iron, 

218-220 
Hanson  &  Van  Winkle  Co.  's  acid  pump, 

233 

belt  strapping  attach- 
ment, 212 

centrifugal  dryer,  164 

electrically        driven 

grinding       motors, 

202-204 

elliptic   anodes,    268- 

270 

independent     spindle 
polishing  and  buff- 
ing lathe,  210,  211 
mechanical       electro- 
plating    apparatus, 
296,  297 
motor-generator  sets, 

109,110 
multipolar     dynamo, 

10),  107 
patent     underwriter's 

rheostat,  140,  141 
plating  room,  179, 180 
separately         excited 

dynamo,  108 
special  rheostat,  141 
union   canvas  wheel, 

207 
universal       polishing 

wheel,  207 
walrine  wheel,  208 
Waverly      voltmeter, 

146, 147 

Hard  nickeling,  312 
Haswell's  patina,  533 
Heating  plating  rooms,  120,  121     • 
Hefner- A Iteneck's    machine,    introduc- 
tion of,  8 

Heliography,  630,  631 
Helios  dip  lacquer,  543 
Helmholtz,  law  of  Faraday  expressed 
by,  60 


Hess'    solution    for     transferring     any 
copper-zinc  alloy,  354 

Hildtbrand,  O. ,  on    regenerative   pro- 
cess of  electro-zincking,  459.  460 

Hollow-ware,  gilding  inner  surfaces  of, 
428 

Holmes  magnetic-electrical  machine,  7 

Hooks  and  eyes,  silvering.  503,  504 

Hossauer's  copper  bath,  328 

Hubl,  experiments  by,  559,  560 

Hummel' s  patent,  145 

Hydraulic  press,  601,  602 

Hydrochlorate  of  zinc,  677 

Hydrochloric  acid,  670 

dilute,  electrolysis  of,  55 
removal    of,    from    the 
pores  of  coppered  ob- 
jects, 339 

Hydrocyanate  of  silver,  083 
zinc.  683 

Hydrocyanic  acid,  670,  671 

Hydro-electric  current,  31 

Hydrofluoric  acid,  672,  673 

Hydrometer  degrees  according  to  Baume" 
and  their  weights  by  volume,  702 

Hydroxyl  groups,  41 

Hydroplatinic  chloride,  679,  680 

Hydrosulphate  of  ammonia,  675 

Hydrosulphuric  acid,  674 

Hvgienic  rules  for  the  workshop,  555- 
557 

Hyponitric  gases,  poisoning  by,  557 

TDIO-ELECTRICS,  28 
-L     Imperial  fluid  measure,  696 
Impurities  in  baths,  prevention  of,  242 
Incrusting  galvanoplasty,  647-649 
Incrustations  with  silver,  gold  and  other 

metals,  403,  404 
Induced  current,  16 
Inducing  current,  16 
Induction,  15-18 

-current,  16 

electric,  discovery  of,  4 

magnetic,  magnitude  of,  15 
Inductor,  97-100 
Insulating  joints,  157 
Ions,  47,  48 

power  of    entering   into  chemical 
processes  possessed  by,  54 

velocity  of,  68.  69 
Iridescent  colors,  473-475 
Iron-ammonium  sulphate,  687 

baths,  475,  476 

management  of,  476,  477 

black  on.  533-535 

blue  on,  535 

brassing  bath  for.  352,  353,  354 


712 


INDEX. 


Iron,  bronze  bath  for,  363 

brown-black    coating   with    bronze 

luster  on.  5S5 
cast,  tin  bath  for.  451,  452 
castings,  unground,  brassing  of,  360 
cleaning  of,  232 
coloring,  533-535 
copper  baths  for,  329,  330 
deposition  of,  475-477 
direct  silver-plating  of,  402 
electrotypes,  657-1)61 
galvanoplastv  in.  657—661 
girders,  zincking  of,  468,  409 
grinding  of,  205 
nickel  bath  for.  262 
nickeled,  prevention  of  rusting  of, 

277,  278 
patina  for,  533 
pickling  of.  218-220 
sheet,  nickeling.  306,  307 

zincking.  466,  467 
silveiing  of,  500 
silvery  appearance  with  high  luster, 

to  give,  535 
tinning  solution  for,  512,  513 

JACOB!.  Prof.,  discovery  of  the  gal- 
vanoplastic  process  by,  5 
Jordan.  C.  J.,  claim  by,  5 
Jordis's  platinum  bath.  445,  446 

standard  formula  for  copper  bath, 

328 
Joule,  law  of,  28 

KAYSER'S  process  of  coloring  brass. 
527.  528 

Kirchhoff,  law  of,  26,  27 
Klein,  production  of  iron  electrotypes 

by.  657 

Ruffe  blades,  nickeling,  310.  311 
Knight's  process  of  coppering   591 
Knives,  calculation  of  lime  for  deposi- 
tion of  determined  weight  on,  127 
nickel  bath  for,  263 
silver-plating  steel  blades  of,  385, 

38.) 
Kohlrausch,  F.  and  W.,  determinations 

by,  60 

Kruel's  brass  bath,  349 
Kugel,  Dr..  discovery  by.  266 
Kuuze's  patent,  609 

T  ACES,  coppering,  649,  650 
Ju     Lacquer,  application  of.  538 

special  invisible,  for  ornamental 

cast  and  chased  interior  grille. 

rail  and  enclosed   work,  541, 

542 


Lacquering.  538-554 
Lacquers,  dead  black,  546-548 
improvements  in,  539 
pyroxyline.  539-541 
requisites  of.  5  '9 
spraying,  548-553 
water-dip.  553,  554 
Lamp-feet,  nickeling  of,  283 
Langbein  &  Co. 's  belt-attachment  com- 
bined with  double  grind- 
ing lathe,  202 
two-polar    and    four-polar 

dynamos,  96 
two-pole  shunt-wound 

dynamo,  104,  105 
voltametric  controlling  ap- 
paratus. 39U-398 
Lathes,  grinding,  200-204 

polishing   208-212 
Law  of  Avogadro,  51 

conservation  of  matter,  33,  53 
Joule.  2<S 
Kirch  Imff1,  26,  27 
Ohm,  22  24 

proposil  ion  deduced  from,  90 
Laws  of  Faraday.  58,  00 
Lead  acetate,  694 

and   tin,  soft  alloys  of,  nickeling, 

311 

anodes.  472,  473 
baths,  472,  473 
cleaning  of.  233 
deposition  of,  472-475 
salts,  poisoning  by,  557 
Leather,  plates    for   the   production  of 

imitation  of.  647 
Leaves,  coppering.  6">0 
Le   Blanc,   decomposition  values  found 

by.  68 

Lecianchg  eel  1,8 1,82 
Le  Fort.  A.  A.,  process  for  silver  de- 
posit on  glass  and  china  by.  652-656 
Lenoir's  process  of  moulding,  643,  644 
Liebenow's  theory  of  t-he  chemical  pro- 
cesses in  the  accumulator,  115,  116 
Light  in  plating  room.  119 
Lime,  burnt  or  quick,  674 
Line,  neutral.  10 
Litmus  paper,  42 
Liver  of  sulphur,  674,  675 
Loadstone,  9 

Liid^sdorff  s  bath  for  coppering,  495 
Lunar  caustic,  691,  692 

MACHINES,  distance  between,  124 
Magnesian  stone,  9 
Magnet,  artificial,  9 
winding,  96 


INDEX. 


713 


Magnetic  field,  11,  13 

induction,  magnitude  of,  15 

iron  ore,  9 

lines  of  force,  flow  of,  13 

machine,  first,  for  the  deposition  of 

silver,  7 
meridian,  10 
needle,  deflection  of,  3,  4 
poles,  10 
Magnetism,  9-11 

and  electricity,  9-69 
remanent  or  residual,  13 
Magnitude  of  the  magnetic  induction,  15 
Main  conductors,  153 
current,  16 
wire,  26 
Manduit's  process  of  bronzing  copper, 

519 
Mannesmann    Pipe    Works    process   of 

plating  aluminium,  486 
Marble,  685 

Marino's  patent,  233,  251 
Mat  dip,  225 

dipping,  224-226 
gilding,  434,  435 

grained  surface,  production  of,  225 
silver,  400 
Matrices  in  plastic  material,  preparation 

of,  596-600 
nickel.  664-667 
Measure,  imperial  fluid.  696 
Measuring  instruments,  144-147 
Mechanical    electro-plating    apparatus, 

295-298 

treatment  during  and  after  electro- 
plating, 213-218 
previous     to     electro-plating, 

188-213 

work,  effect  of,  52 
Meidinger  cell,  74,  75 
Mercuric  nitrate,  691 
Mercurous  nitrate,  690,  691 
Mercury  salts,  poisoning  by,  557 
Meridian,  magnetic,  10 
Men  ten's   process   for   black    on    iron, 

534,  535 

Metal,  content  of,  in  metallic  salts,  700 
matrices,  602-609 

detaching  moulds  from,  617 
Metallic  alloys,  first  deposition  of,  7 
moulds,  636,  637 
objects,  preparation  of,  188-246 
paint,  preparation  of,  652,  653 
salts,  content  of  metal  in,  700 

decomposition-value    of    solu- 
tions of.  68 

Metallization  by  dry  way,  640.  641 
wet  way.  641-643 


Metallized  silver,  preparation  of,  652 
Metallizing  moulds.  640-643 
Metal lo-chromes,  473-475 
Metalloids,  classification  of,  40 
Metallometric  balances,  388-391 
Metals  and  non-metals,  38-40 

classification  of,  40 

coloring  of,  516-537 

incrustations  with,  403,  404 

series  of  electro-motive  force  of,  30 

solution-tension  of,  61-63 

specific  resistance  of,  25,  26 
Mirrors,  coppering,  651 
Mixed  coupling.  89 
Molecular  weights  of  dissolved  bodies, 

method  of  determining,  50,  51 
Molecule,  33 

Molecules,  dissociation  of,  50 
Monopotassic  carbonate,  684 
Montgomery,  Dr.,  introduction  of  gutta- 
percha  by,  6 

Motor-generators,  109,  110 
Mould,  detaching  deposit  from,  615-617 

holder,  614 

suspension  of,  in  the  bath,  615 
Moulds,  electrical  contact  of,  613-615 

further  manipulations  of,  610 

gelatine,  644,  645 

in  plastic  material,  preparation  of, 
596-600 

making  the,  conductive,  610-613 

metallic,  636,  637 

metallizing  or  rendering  conduct- 
ive, 640-643 

non-metallic,  rendering  of,  imper- 
vious. 640 

plaster  of  Paris  for  casts,  637-639 
Miiller  and  Behntje,  investigations  by, 

579 

Multipliers.  11,  12 
Muriate  of  gold,  679 
zinc,  677 

Muriatic  acid,  670 
Murray,  discovery  by,  5 
Mylius  and  Fromm,  researches  by,  560 

NAILS,  zincking,  471 
Nature  printing,  645,  646 
Needles'  eyes,  coppering,  498 
Negative  electricity,  29,  47 
Nernst's  osmotic  theory  of  production 

of  current,  63-65 
theory,  31 

Neubeck's  iron  electrotypes,  660 
tin  bath,  453 
voltametric   controlling  apparatus, 

394-596 
Neutral  line  or  zone,  10 


714 


INDEX. 


Neutral  salts,  44,  46 

Neutralization,  42 

Nicholson  and  Carlisle,  decomposition 

of  water  by.  3 

Nickel  alloys,  deposition  of.  314,  315 
-ammonium  sulphate,  688.  689 
and  cobalt,  deposition  of,  247-323 
anodes,  268-275 

reddish  tinge  on,  274,  275 
solution  of,  275 
bath,  black,  260,  261,  262 

coupling  cells  for,  133,  134 
current-strength  required   for, 
,      125 

without  nickel  salt,  264 
baths,  additions  to.  250-252 
carbon  disulphide  in,  263 
cold,   thick   deposits   in,    267, 
-      268 

correction  of  reaction  of,  265 
effect  of  current-density  in,  252' 
electro-motive  force  for,  252 
examination  of,  316-323 
faulty  arrangement  of  anodes 

in,  281.282 
formulas  for,  253-264 
hot,  thick  deposits  in.  265-267 
insoluble  anodes  for,  271,  272 
mixed  anodes  for,  257,  258 
polarization     phenomena     in, 

284,  285 
proportion    of    cast    to   rolled 

anodes  in.  273,  274 
reaction  of,  252,  253 
recovery  of  nickel  from  old,  314 
refreshing,  2HO,  291 
suspension  of  objects  in,  278 
working  of,  264 
-bronze,  315 
carbonate,  685,  686 
chloride.  678 

copper-zinc  alloy,  deposition  of,  315 
deposition  of,  247-323 
deposits,  polishing  of,  216 

thick,    in    cold    nickel    baths, 

267,  268 
in  hot  nickel  baths,  265- 

267 

very  thick,  262,  263 
electrotypes,  661-664 
galvanoplasty  in,  661-667 
matrices,  664-667 
objects,  polished,  cleaning  of,  291, 

292 

properties  of,  247,  248 
recovery  of.  314 
salts,  248.  249 

prepared,  264,  265 


Nickel,  scratch  brushes  for,  214 

solutions,  eruptions  caused  by,  556 

sulphate,  688 

various  colors  on,  525 
Nickeled  objects,  freeing  of,  from  moist- 
ure, 216 

Nickeling  by  contact  and  boiling,  491- 
494 

black,  260-262 

burnt.  278,  279 

cavities  and  profiled  objects,  282- 
284 

current  density  for,  279-281 

dark,  259,  260 

defective,  resume"  of.  288-290 
stripping.  285-288 

execution  of,  275-285 

hard,  312 

knife  blades,  310,  311 

operation,  calculation  of,  292,  293 

printing  plates,  312-314 

quick,  2ii6 

security  against  rust  in,  276-278 

sharp  surgical  instruments,  310,  311 

sheet-zinc,  2:t8-306 

small  and  cheap  objects,  293-298 

soft  alloys  of  lead  and  tin,  311 

tin-plate,  306 

treatment  of  articles  after,  291 

wire,  307-309 

yellowish  tone  of,  remedy  against, 

288 

Niel,  imitation  of,  404.  405 
Niello,  Corvin's.  646,  647 
Nitrate  baths,  580,  581 

of  mercury,  691 
Nitrates,  46,  690-692 
Nitre.  690- 
Nitric  acid,  670 

Nitrous  gases,  poisoning  by,  557 
Nobili,  production  of  iridescent  colors 

by,  4 

Nobili' s  rings,  473-475 
Noe's  thermo-electric  pile,  91 
Non-electrics,  29 
Normal  salts,  46 
North  pole,  10 

Numerical  data,  useful,  table  of,  696 
Nuts,  zincking,  471 

OERSTED,     Prof.,     discoveries    by, 
3,4 

Ohm,  22 
Ohm,  law  of,  4,  22-24 

proposition  deduced  from,  90 
Oil  gutta-percha,  moulding  with,  635, 

636 
preparation  of,  636 


INDEX. 


715 


Oil  of  vitriol,  669,  670 

Old  brass  or  brush-brass  finishes,  543, 

544 

gold,  432,  433 
silvering,  405 
Optical    instruments,    brass,    black    on, 

526,  527 

Organic  acids,  salts  of,  692-694 
Orpiment,  675,  676 
Osmotic  laws,  value  of,  50 
pressure,  49,  50 

theory  of  the  production  of  the  cur- 
rent, 63-65 
Ostwald,  Faraday's  law  expressed  by, 

60,  61 

Over-nickeling,  278,  279 
Oxidized  silvering,  405,  406 
Oxy-acids,  41 

PACINOTTI'S  ring,  invention  of,  7 
Paint,    metallic,     preparation    of, 

652,  653 

Painter's  gold,  416 
Palladium,  deposition  of,  448,  449 

properties  of,  448 
Paracyanide.  336 
Parallel  coupling  of  cells,  89 

dynamos,  172-175 
Parkes'    process  of   metallization,  642, 

643 
Patina,  522 

artificial,  522-524 
blue-green,  524 
brown,  524 

genuine,  imitation  of,  523 
Patinizing,  522,  523 
Pfanhauser  on  reddish  tinge  on  nickel 

anodes,  274,  275 
scattering    of    current- 
lines,  132,  275 

remedy  for  yellowish  tone  of  nickel- 
ing by,  238 

voltametric  balance  of,  391-394 
Philip's  process  of  coppering  laces  and 

tissues,  649,  650 
Phosphates,  46,  692 
Photo-engraving,  625-627 

-galvanography,  626,  627 
Pickling  and  dipping,  218-228 
objects  to  be  silvered,  382 
Pile  of  Volta.  2 
Pilet's  palladium  bath,  449 
Pins,  silvering,  503,  504 
Pipes,  zincking  of.  467.  468 
Pitchers,  gilding  inner  surfaces  of,  428 
Pixii,    first   electro-magnetic   induction 

machine  by,  4 
Plante"s  accumulator,  111,  112 


Plaster  of  Paris  moulds  for  casts,  637- 

639 

rendering  of,  imper- 
vious, 639,  640 
Plastic   objects,   galvanic    reproduction 

of,  634-645 

Plating,  rapid,  coupling  cells  for,  135 
room,  floor  in,  121,  122 
heating  of,  120,  121 
light  in,  119 
renewal  of  water  in,  121 
size  of,  122 

ventilation  of,  119,  120 
Platinic  chloride,  679,  680 
Platinizing  by  contact.  511 
Platinum  anodes,  271,  272 

for  gold  baths,  421,  423 
baths,  444-446 

management  of,  446 
recovery  of  platinum  from,  448 
deposition  of,  444-448 
deposits,  burnishing  of,  216,  217 
plating,  direct,  447,  448 

execution  of,  446-448 
properties  of,  444 
recovery  of,   from  platinum  baths, 

448 

Plunge  batteries,  84-87 
Poisoning  by  chemicals,  556,  557 
Polarization,  65-67 

current,  appearance  of,  66,  67 
electro-motive  counter-force  of,  130- 

132 
phenomena  in   nickel   baths.    284r 

285 

Poles,  magnetic,  10 

Polished  objects,  cleansing  of,  217,  218 
Polishing,  206-212 

and  grinding  rooms,  122,  123 
deposits.  216,  217 
lathes,  208-212 
machines,  automatic,  300,  301 
materials,  212,  213 
wheels,  207,  208 

Poole,  Moses,  first  use  of  thermo-elec- 
tricity by.  7 

Porcelain  ware,  galvanoplastic  decora- 
tions on,  651-656 
Positive  electricity,  29 

electrode,  47 
Potash,  684 

-alum,  686 

Potassium-ammonium  sulphate,  686 
and  sodium,  amalgams  of,  4 
bitartrate,  692,  693 
carbonate,  684 

in  silver  baths,  determination 
of,  409-411 


716 


INDEX. 


Potassium  cyanide.  (180-682 
as  a  pickle,  224 
determination  of.  in  brass 

baths,  360,  361 
of,    in    copper    baths, 

343-345 

first  use  of  solutions  of  me- 
tallic cyanides  in,  6 
handling  of,  556 
poisoning  by,  556 
discovery  of,  3 
disulphide,  electrolysis  of  solution 

of,  54,  55 
ferrocvanide,  683 
hydrate,  673 
nitrate,  690 
-sodium  tartrate,  693 
sulphide,  674,  675 
Potential,  30 

difference  of,  21 
Preece's  test,  456 
Preliminary  pickle,  223 
Presses,  600-602 
Pretsch,  invention   of  heliography  by, 

630 
Primary  current,  16 

salts,  46 

Prime  &  Son.  early  use  of  a  magnetic 
machine  for  the  deposition  of  silver 
by,  7 
Printing  plates,  nickeling,  312-314 

steeling,  advantage  of,  477 
Proctor,  Chas.  H..  on  electro-chemical 

cleaning.  230,  231 
on  red  gold  solution, 

432. 433 

silver-plating      the 
steel     blades     of 
knives,  385,  386 
Protosulphate  of  iron.  687 
Prussia te  of  silver,  683 

of  zinc,  683 
Prussic  acid.  670,  671 

poisoning  by,  556 
Pump-pistons,  coppering,  656 
Pyridine  in  zinc  baths,  461 
Pyrophosphates,  692 
Pyroxyline  lacquers,  539-541 

rvUADRIVALENT  elements,  38 

T)  AIL  work,  interior,  lacquer  for,  541, 
Xl     542 

Rapid  galvanoplasty,  587-593 
baths  for,  590,  592 
Ratsbane,  672 
Reaction  of  baths.  245,  246 


Reagent  papers,  42 

Raoult's   method    of    determining   the 
molecular  weights  of  dissolved  bodies, 
50,  51 
Recovery  of  silver  from  old  silver  baths. 

412-414 
Red  gilding,  430,  431 

sulphide  of  antimony,  675 
Reform  wheel,  198 
Remanent  magnetism,  18 
Reprinting,  628 
Reproduction,  558 
Residual  magnetism,  13 
Resinous  electricity,  29 
Resist,  507 

Resistance  board,  136 
electric,  unit  of,  22 
of  electrolyte,  128-130 
Resistances,  specific,  1*4-26 
Retort-carbon  anodes,  271 
Rieder's   process   of  electro-engraving, 

631-634 

Ring  armature,  97,  98 
Rings,  plating  of,  with  red  gold,  431 
Ritter,  production  of  secondary  currents 

by, 111 

Rivets,  zincking,  471 
|  Rheostat,  136 
•  Rochelle  salt,  693 
!  Rock  salt,  676 

|  Rojas,  F.   Arquimedas,  process  for  the 

production    of    colors   on    metals  by 

electro-deposition    invented    by,  536, 

537 

I  Rolls  of  steel  and  cast-iron,  coppering, 

656 
Rose-color  gilding,  432 

gold  solution,  432,  433 
Roseleur's  brass  baths,  850,  351,  353 
copper  bath,  328,  329,  334 
metallometric  balance,  388-391 
method    of    preparing    solution    of 

sodium  sulphite,  501,  502 
tin  bath,  450,  451,  511 
Rouge,  212 
Ruby  oxide,  334 
Ruolz's  bronze  bath,  363 
Russell  and  Woolrich's  brass  bath,  349 

SAL  AMMONIAC,  676 
Salt,  common,  676 
Saltpetre,  690 
Salts,  41-45 

conducting,  249,  250 
formation  of,  from  the  acids,  44 
nomenclature  of,  45,  46 
nickel.  248,  249 
of  organic  acids,  692-694 


INDEX. 


717 


SalzSde's  brass  bath,  349 

Sand,  H.,  on  agitation  of  baths,  238 

Sand-blast,  types  of,  193,  194 

Satin  finish  lacquer,  542 

Sawdust  for  drying  objects,  163 

Saw-table,  618,  619 

Scarnoni,  improvement  of  heliography 

by,  630 

Scheele,  observations  by,  6 
Schneider,     Wm.,    zinc     bath     recom- 
mended by,  463 
Schonbeck's galvanoplastic copper  bath, 

586 

Schuckert's  machine,  introduction  of,  8 
Schultz,  O.,  patent  of,  339 
Scissors,  nickel  bath  for.  263 
Scratch-brush,  construction  of  a,  191, 192 
-brushes,  189,  190 
-brushing.  189-192 
deposits,  213-215 
liquids  used  in,  214 
Screws,  zincking,  471 
Secondary  cells,  111-118 
current,  16 
salts,  46 

Sectional  silver-plating,  384 
Seignette  salt,  693 
Self-excitation,  97 
Separate  excitation.  97 
Series  coupling  of  dynamos,  172-175 

-wound  dynamos,  103 
Shaving  machines,  619.  620 
Shell,  backing,  617,  618 

detaching  the,  from  the  mould,  615- 

617 

gold,  416 
Sheet-iron,  nickeling,  306.  307 

zincking.  466.  467 
metal,  electrolytic  pickling  of,  221 
steel,  nickeling.  306,  307 
Sheets,  iridescent,  production  of,  475 

large,  polishing  lathe  for.  209 
Shunt-wound  dynamos,  103-105 
Siemens'  machine,  introduction  of,  8 
&   Halske  machines,    introduction 

of,  8 
Silver  alloys,  380,  381 

and  gold,  galvanoplasty  in.  667.  668 
bath,  coupling  cells  for.  133,  134 

electrolysis  of  a,  57 
baths,  366-370 

additions  of  organic  substances 

to,  377-379 
agitation  of,  375-377 
determination   of  proper  pro- 
portions of  silver  and  excess 
of  potassium  cyanide  in,  375 
examination  of,  409-412 


Silver  baths,  insoluble  anodes  in,  372 

old,   recovery  of  silver  from, 

412-414 

steel  sheets  as  anodes  for,  373 
tanks  for,  370 
thickening  of,  374 
treatment  of.  370-275 
brown  tone  on   406,  407 
calculation  of  time  for  deposition  of 

determined  weight  of,  127 
chloride,  678,  "79 

preparation  of  silver  bath  with. 

368  369 
cyanide,  683 

deposit,  calculation  of  the  weight 
of,  from  the  current-strength 
used,  398-400 
heavy,  baihs  for,  368-370 
on  glass  and  china,  652-656 
deposition  of.  365-414 
deposits,  burnishing  of,  216,  217 

polishing,  401 
determination  of  weight  of  deposit 

of,  386-398 
frosting.  400  401 
galvanoplasty  in,  667,  668 
in   silver   baths,  determination  ofT 

411.  412 

incrustations  with,  403,  404 
mat,  400 

metallized,  preparation  of,  652 
nitrate,  691,  692 
plating,  determination  of.  408 
execution  of,  382-400 
culinary,  401,  402 
sectional.  384 
propei ties  of.  365 
recovery  of,  from  old  silver  bathsr 

412-414 

sheets,  brushing  of,  206 
Silvered  articles,  stripping,  407,  408 
Silvering,  antique,  405 
by  contact,  499.  oOO 
immersion.  500-504 
weight,  baths  for,  368-370 
cold,  with  paste,  504,  505 
copper  wire,   10 J 
current-density  for,  125 
mechanical  and  chemical  prepara- 
tion of  objects  for,  382,  383 
nielled,  404,  405 
old.  405 

ordinarv,  bath  for,  370 
oxidized,  405,  -;06 
slinging  wires  for,  383 
yellow  tone  of,  379 
Sine  galvanometer.  12 
Skates,  nickeling,  311 


718 


INDEX. 


Slinging  wires,  160 
Smee  cell,  72,  73 

Sraee,  Dr.  Alfred,  discoveries  in  electro- 
deposition  by,  6 

experiments  by,  559 
Sodium  and  potassium,  amalgams  of,  4 

-bicarbonate,  684,  685 

bisulphite,  689,  690 

carbonate,  684 

chloride,  67G 

citrate,  694 

discovery  of,  3 

hydrate,  673 

hydroxide,  electrolysis  of,  55,  56 

nitrate,  690 

phosphate,  692 

pyrophosphate,  692 

sulphate,  686 

sulphite,  689 

preparation  of  solution  of,  501- 

503 
Solder,  hard,  removal  of,  from  bicycle 

frames,  221,  222 
Solenoid,  15 

Solution-tension  of  metals,  61-63 
Solutions,  theory  of,  48,  49 
Solvents,  233,  234 
Sources  of  current,  70-118 
South  pole,  10 
Specific  gravity  of  baths,  235,  236 

resistances,  24-26 
Spencer,  T. ,  claim  by,  5 
Spoons,  calculation  of  time  for  deposi- 
tion of  determined  weight  on,  127 

extra  heavy  coating  of  silver  on, 

383,  384 

Spirit  of  nitre,  670 
Spirits  of  hartshorn,  673,  674 
Spraying  lacquers,  548-553 

machine,  548,  549 
Springs,  coppering,  498 
Stairs,  coppering  parts  of,  656.  657 
Stannic  chloride,  677 
Stannous  chloride,  677 
Steam  drying  barrel,  164 

sawdust  box,  163 
Steel  anodes  for  gold  baths,  421-423 

baths,  475,  476 

blue  on,  535 

brassing  bath  for,  353,  354 

cleaning  of,  232 

copper  baths  for,  329,  330 

direct  silver-plating  of,  402 

galvanoplasty  in,  657-661 

grinding  of.  205 

gun  barrels,  coppering,  656 

nickeled,  prevention  of  rusting  of, 
277,  278 


Steel  pens,  coppering,  498 

plates,  etching,  630 

rolls,  coppering,  656 

sheet,  nickeling,  306,  807 

sheets  as  anodes  for  silver  baths,  373 

silvering,  500 

tanks,  welded,  154 

tapes,  zincking,  469-471 

tinning  solution  for,  512,  513 
Steeling,  475-477 

execution  of,  477 
Steinach  and  Buchner's  table  for  use  of 

barium  cyanide  solution,  410,  411 
Stereotypes,  coppering,  622,  623 

nickeling.  312-314 
Stirring  contrivances.  ri83 
Stockmeyer's  copper  bath,  330 

standard  formula  for  copper  bath,  328 
Stoehrer's  plunge  battery,  86 
Stolba's  process  of  nickeling,  491,  492 

tinning  bath,  514 
Stoneware,  coppering,  650 

tanks.  154 

Stopping-off,  402.  403 
Stripping  acid,  286 

defective  nickeling,  285-288 

gold  from  gilded  articles,  440,  441 

silvered  articles,  407,  4C8 
Sugar  of  lead,  694 
Sulphate  of  iron,  687 
Sulphates,  46 

and  sulphites,  686-690 
Sulphur  combinations,  674-676 
Sulphuretted  hydrogen,  674 

poisoning  by,  557 
Sulphuric  acid,  669,  670 

electrolysis  of,  66 

Sulphurous  acid,  poisoning  by,  557 
Sulphydrate  of  ammonia,  675 
Sulphydric  acid,  674 
Surgical  instruments,  sharp,  nickeling, 

310,  311 
Swiss  mat,  535 
Switch-boards,  180-183 
Symbols  of  chemical  elements,  34,  36 
Synthetic  chemical  process,  32 
Szirmay   and   von    Kollerich  on   addi- 
tions to  zinc  baths,  460 

rpABLE  for  freeing  objects  from  grease, 

161-163 

Table  for  inter-conversion  of  certain 
standard  weights  and  meas- 
ures, 697,  698 

of  bare  copper  wire  for  low  volt- 
age, 702 

chemical  elements  with  their 
symbols  and  atomic  weights, 
35 


INDEX. 


719 


Table  of  content  of  metal  in  metallic 

salts,  700 
electrical    resistance    of    pure 

copper  wire,  701 
electro-chemical     equivalents, 

61 

hydrometer  degrees  according 
to  Ban  me",  and  their  weight 
by  volume,  702 

resistance  and  conductivity  of 
pure  copper  at  different  tem- 
peratures, 701 

solubilities   of  chemical   com- 
pounds    used     in      electro- 
technics,  698,  699 
useful  numerical  data,  696 
Tacks,  zincking,  471 
Tampico  brush,  205 
Tangent  galvanometer,  12 
Tanks,  154-157 

for  brass  baths,  355 

galvanoplastic  baths,  587 
gold  baths,  421-426 
potassium-copper  cyanide  baths, 

835,  356 
silver  baths,  370 
zinc  baths.  465 
Tartar  emetic,  693 
Tea  sets,  galvanoplastic  decorations  on, 

651 
Temperature,  coefficient  of,  26 

of  baths,  236,  2  JO 
Terchloride  of  gold,  679 
Terra-cotta  objects,  coppering,  650 
Thermo-electric  piles,  7,  90  93 

-electricity,  first  use  of,  7 
Thermometer    degrees,    conversion    of 
Fahrenheit  to  Centigrade,  and  Centi- 
grade to  Fahrenheit.  696 
Thermometers,  coppering  mercury  ves- 
sels of,  651 
Thompson,  Sylvanus,  cobalt  solution  of, 

324 

Three-wire  system  of  current-distribu- 
tion, 180 
Tin  baths,  450-452 

management  of,  452 
chloride,  677 
coloring,  536 
deposition  of,  450-453 
deposits,  polishing  of,  216 
direct  silvering  of,  401,  402 
patina  for,  533 
plate,  nickeling,  306 
plating,  process  of,  452,  453 
properties  of,  450 
salt,  677 
sepia  brown  tone  on,  536 


Tinning  by  contact  and  by  boiling,  511- 

514 

Tissues,  coppering,  649,  650 
Toggle  press,  6UO,  601 
Tombac  bath,  362,  363 

cleaning  of,  232,  233 

deposition  of,  362,  363 

pickling  of.  223,  224 
Touchstone,  testing  gold  by,  415,  416 
Transmission,  124 
Trivalent  and  quinquavalent  elements,  38 

elements,  38 
Trough  battery,  2,  71 
Tumblers,    galvanoplastic     decorations 

on,  651-656 

Tumbling  barrel  or  drum,  194-196 
Two-polar  dynamo,  96 
Type  matrices,  preparation  of.  623 

metal,    stereotypes    of,    nickeling, 
313, 314 

TTMBRELLA  handles,  celluloid,  gal- 
«J      vanoplastic  decorations  on,  656 
Union  canvas  wheel,  207 
Units,  electric,  18-24 
Univrtlent  elements,  38 
Universal  polishing  wheel,  207 

VALENCE  of  chemical  elements,  36- 
38 

Van't  Hoff,  investigations  of,  48,  50 
Vapor-pressure,  61 
Varrentrapp's  iron  bath.  475,  476 
Vases,  galvanic  reproduction  of,  634-645 
Ventilation  of  plating  room,  119,  120 
Verdigris,  693,  694 
Vessels,  contents  of,  695 
Vienna  lime,  199,  212 
Villon's  process  of  plating  aluminium, 

485 

Vitreous  electricity,  29 
Volt,  21 

ampere.  21 

Volta,  discovery  of,  2 
Voltage,  low,  table  of  bare  copper  wire 

for,  702 
Voltaic  cell,  31 
cells,  70-84 
pile,  2 
Volta  metric  balance,  391-394 

controlling  apparatus,  394-398 
Voltmeter,  144-147 
switch,  147-151 
Volumetric  analysis,  318,  319 

determination  of  copper  in  copper 
baths,  346-348 
zinc      in       brass 
baths,  362 


720 


INDEX. 


WALENN'S  copper  ba.th,  335 
Walrine  wheel,  208 
Warren's  cobalt  solution,  324,  325 
nickel  and  cobalt  solution,  295 
Washing  soda,  684 
Watch  chains,  plating  of,  with  red  gold, 

431 
movements,    palladium     bath     for 

plating,  449 

Watches,  graining  parts  of,  505-508 
Water,  233,  234 

current  of,  comparison  of  the  elec- 
tric current  with,  19,  20 
decomposition  of,  by  electrolysis,  3 
-dip  lacquers,  553,  554 
renewal  of,  in  plating  rooms,  121 
Watt.  21 

Watt's  lead  bath,  472 
Waverly  voltmeter,  146,  147 
Wax  compositions  for  moulding,  598 

melting  kettles,  599 
•  mould,  detaching  deposit  from,  616, 
,     617 

electrical  contact  of,  614,  615 
moulding  in,  597-t  00 
Weight,  avoirdupois,  695 
Weights  and   measures,  table   for   the 

inter-conversion  of.  697 
Weill,  and  Newton's  bronze  bath,  363 

copper  bath  by,  334,  335 
Weston  ammeter,  147 

boric  acid  in  nickel  baths,  recom- 
mended by,  250 

Wheatstone's  machine,  introduction  of,  8 
Wheels,  grinding,  199,  200 

polishing,  207,  208 
White  arsenic.  672 

prussiate  of  potash,  680-682 
vitriol,  688 
Wilde's  machine,  7 
Wire,  coppering,  498 
gilding,  4S7-440 
nickeling,  307-309 
zincking,  469-471 
Wires,  26 

Wollaston,  discovery  by,  3 
Wood  cuts,  bath  for.  590 
Wooden  tanks,  155,156 
Woolrych,  first  magnetic  machine  for 

the  deposition  of  silver  by,  7 
Workshop,  hygienic  rules  for,  555-557 
Wright,  first   use   of  solutions  of  the 
metallic  cyanides  in  potassium  cya- 
nide by,  6 
Wrought  iron,  pickling  of,  218 

TfELLOW  prussiate  of  potash,  683 


Z  ILK  EN'S  bath   for  tinning  by  con- 
tact, 512 

Zinc  alloys,  production  of,  471,  472 
amalgamation  of,  71,  72 
anodes,  463-465 
baths,  4-58-463 

tanks  for,  465 
black  on,  531,532 
blue-black  on,  532 
brassing,  bath  for,  353 
bronzing  on,  533 
brown  patina  on,  532 
carbonate,  685 
castings,  brushing  of,  206 
chloride,  677 

solution,  electrolysis  of,  67 
coloring,  531-533 
copper  bath  for,  333,  334 
cyanide,  683 

determination  of,  in  brass  baths,  36T 
deposition  of,  453-472 
etchings,  nickeling,  313,  314 
gray  coating  on,  533 

-yellow,  brown  to  black  on,  532 
lamp-feet,  nickeling  of,  283 
nickel  bath  for,  259 
patina  for,  533 
pickling  of,  223 
plates,  coppering,  623 
properties  of,  453 
scratch-brushes  for,  214 
sheet,  brassing  of,  previous  to  nick- 
eling, 302,  303 

coppering  of,  previous  to  nick- 
eling, 303,  304 

freeing   of,  from   grease,  301, 
302 

nickeled,  polishing  of,  305, 306 

nickeling  of,  298-306 

polishing  of,  206,  299,  300 
red  brown  shade  on,  533 
sulphate.  688 
tin  bath  for,  451,  452 
volumetric     determination    of,    in 

brass  baths,  362 
yellow-brown  shades  on,  533 
Zincking  by  contact,  514,  515 
execution  of,  465,  466 
pipes,  467,  468 
profiled  objects,  468,  469 
regenerative  process  of,  459,  460 
screws,    nuts,    rivets,    nails,   tacksr 

etc.,  471 

sheet-iron,  466,  467 
wire,  469-471 

wrought  iron  girders.  468,  469 
Zincography,  627-630 
Zone,  neutral,  10 


The  Hanson  fr  Van  Winkle  Company,  Newark,  N.J.,  U  S. 

MULTIPOLAR  TYPE  DYNAMOS 

VXT'E   manufacture   and    are 
prepared    to   furnish  this 
type  dynamo  in  sizes  ranging 
from  50-10,000  amperes,  either 
shunt  or  compound  wound,  or 
with  fields  wound 
for  separate  exci- 
tation.     We  can 
absolutely  recom- 
mend   this    type 
machine    as    the 
most  modern  and 
complete  plating 
dynamo    on    the 
market. 

We  can  supply  low 
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rect connected  to 
motor  of  suitable  size, 
the  whole  outfit 
mounted  on  a  sub- 
stantial ironsub-base. 

Motors  can  be  fur- 
nished in  any  voltage 
to  suit  conditions. 


THE  HANSON  &  VAN  WINKLE  COMPANY 

U.  S.  A. 
Main  Office,  No.  269  Oliver  St.  NEW  YORK,  CHICAGO,  ILL. 

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Morrow  Ave.,  Toronto,  Ont.  I 


The  Hanson  «£•  Van  Winkle  Company,  Newark,  N.J.,  U.  S.  . 
The  H.  &  V.  W. 

Patented  Underwriter's  Rheostats 

For  Electroplating  TanKs 


Made  in  all  Sizes  to  suit  requirements 
WE,  MANUFACTURE: 

Multipolar  Dynamos  in  various  sizes,  giving  5  and  10  volts,  and  ranging 
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10,000  amperes  on  two-wire  system. 

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Special  itemized. estimates  furnished  for  complete  plants. 
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THE  HANSON  &  VAN  WINKLE  CO. 


Main  Office 

No.  269  Oliver  St. 

Newark,  N.  J. 


U.  S.  A. 

New  York 

No.  79  Walker  St. 


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The  Hanson  Sr  Van  Winkle  Company,  Newark,  N.J.,  U.  S.  ^. 

United  States  Patents  June  22,  1897— February  24,  1903— Oct.  11,  1904, 

March  24,  1908 -May  19,  1908. 
Canadian  Patents  Nos.  58,205  and  97,852. 

Other  Patents   P    tiding. 


THe  H. 


V.    W. 


Mechanical   E,leetro-Plating  Apparatus 

Type    B.        Gear  Drive. 

Used  in  Plating  Nickel,  Copper,  Brass,  Bronze, 

These  machines  are  particularly  adapted  for  electro-plating  quantities 
of  small  work  in  bulk,  saving  time,  labor,  and  expense.  They  have  for  a 
long  time  been  a  recognized  necessity  in  the  metal  manufacturing  industry. 

Our  patented  perforated  celluloid  panel  construction  is  particularly 
adapted  for  use  with  very  small  work.  These  panels  are  made  with  round 
perforations  as  small  as  TV  in.  and  with  oblong  perforations  \  x  ^  in.  The 
celluloid  being  thin  and  tough  allows  for  free  circulation  of  the  solution. 

We  have  installed  over  800  of  these  outfits,  many  of  them  among  the 
largest  and  best  known  manufacturers  in  the  United  States  and  Canada, 
which  are  giving  perfect  satisfaction. 


THE  HANSON  &  VAN  WINKLE  CO. 


Newark,  N.  J. 
269  Oliver  Street 


New  York 
79  Walker  Street 


Chicago,  111. 
110  North  Clinton  St. 


Canada  Office:  Canadian  Hanson  &  Van  Winkle  Co. 
Morrow  Ave.,  Toronto,  Ont. 


The  Hanson  Sr  Van  Winkle  Company,  Newark,  N  J.,  U.  S.  Jl. 


NICKEL  ANODES 


WITH  the  advances  made  in 
nickel  plating  in  the  past 
years  the  tendency  has  been 
to  use  larger  containers,  which 
naturally  require  anodes  of  increas 
ed  dimensions.  To  meet  this  ne- 
cessity various  devices  have  been 
tried  in  the  way  of  crowding  a  lar- 
ger number  of  plates  into  the  tank 
or  using  irregular  shapes,  some- 
times with  cumbersome  attach- 
ments. After  exhaustive  experi- 
ments we  have  at  last  solved  the 
question,  and  now  offer  to  the  trade 
our  patented  Elliptic  anode. 

For  many  years  it  has  been  cus- 
tomary to  use  flat  nickel  Anodes, 
only  because  there  was  nothing  else 
obtainable,  and  these  flat  plates  are 
still  in  general  use  in  many  large 
establishments,  which  have  not  tak- 
en time  to  investigate  the  decided 
advantage  and  economy  in  our  late 
developments. 

The  patented  Elliptic  Anodes 
possess  many  points  of  real  merit; 
they  are  the  result  of  careful  ex- 
periments covering  several  years, 
and  they  overcome  the  disadvant- 
ages in  all  other  shapes. 

Elliptic  Anodes  are  2^  inches 
wide  by  i%  inches  thick,  and  are 
cast  in  any  ordinary  length. 

Experience  showsthat  all  Anodes 
work  more  from  the  edges  than 
from  the  centre,  showing  conclu- 
sively that  circulation  around  the 
Anode  is  necessary  to  get  the  great- 
est amount  of  corrosion  or  disin- 
tegration. 


THE  HANSON  &  VAN  WINKLE  CO. 

U.  S.  A. 

Newark,  N.  J.  New  York  Chicago,  111. 

269  Oliver  Street  79  Walker  Street  110  North  Clinton  St. 

Canada  Office:  Canadian  Hanson  &  Van  Winkle  Co. 
4  Morrow  Ave.,  Toronto,  Ont. 


The  Hanson  Sr  Van  Winkle  Company,  Newark,  M.J.,  U.  S.  ^?. 

Electro- Galvanizing' 

Cold  Process.  No  Royalties 


Complete  Outfits  Furnished 


Samples    Finished   Without  Charge,  Estimates 
and  Information  Furnished  On  Request. 


An  Economical  and  Practical  Substitute  For  Hot  Galvanizing 

We  have  fitted  up  a  large  number  of  plants  which  are  operating  pro- 
fitably at  an  increased  economy  over  the  old  method.  The  Electro-depo- 
sition of  Zinc  has  been  attempted  for  many  years,  but  within  a  short  period 
only  have  practical  commercial  results  been  obtained.  With  the  advan- 
tages secured  by  the  use  of  our  Compound  Wound  Dynamos  as  a  source  of 
current,  we  are  now  prepared  to  fit  up  complete  plants  for  galvanizing  all 
iron  or  steel  articles,  from  small  castings  to  a  ship's  anchor  and  chain. 


A  PLANT  FOR  ELECTRO-GALVANIZING  COMPRISES 

Special  Low  Voltage  Compound  Wound  Dynamo. 
Electrical  Measuring  Instruments. 

tlectrical  Connections. 
Tank  or  Tanks  for  Solution,  with  Fittings. 

Solution  or  Material  for  Solution. 

Cast  Anodes  of  superior  quality  are  absolutely  without  Waste. 

Cleaning  Outfit  for  preparing  work,  including  all  tanks  and 

supplies  necessary. 

WHEN  REQUIRED  WE  SEND  OUR  EXPERT  FOR 
LARGE  INSTALLATIONS. 


THE  HANSON  &  VAN  WINKLE  CO. 

Newark,  N.  J.  New  York  Chicago,  111. 

269  Oliver  Street  79  Walker  Street  110  North  Clinton  St. 

Canada  Office:  Canadian  Hanson  &  Van  Winkle  Co. 

Morrow  Ave.,  Toronto,  Ont.  5 


The  Hanson  fr  Van  Winkle  Company,  Mewark,  X.  J.,  U.  S. 


Aluminum  Dipping  Baskets. 

We  illustrate  herewith  our  patented  perforated  sheet  aluminum  dipping 
baskets,  also  aluminum  wire  baskets  which  we  are  prepared  to  furnish  in 
any  style  or  shape. 


Aluminum  dipping  baskets  are  practically  acid  proof  but  must  not  be 
used  in  potash,  muriatic  or  hydrofluoric  acid.  They  are  particularly  adap- 
ted for  use  in  washing  and  dipping.  After  a  thorough  test  we  do  not  hes- 
itate to  recommend  them.  They  are  very  light,  very  durable  and  will  out- 
last the  ordinary  dipping  baskets. 


THE  HANSON  &  VAN  WINKLE  CO. 


Newark,  N.  J. 
269  Oliver  Street 


u.  S.  A. 

New  York 
79  Walker  Street 


Chicago,  111. 
110  North  Clinton  St. 


Canada  Office:  Canadian  Hanson  &  Van  Winkle  Co. 
Morrow  Ave.,  Toronto,  Ont. 


CATALOGUE 

OF 

Practical  and  Scientific  Books 

PUBLISHED    BY 

Henry  Carey  Baird  &  Co. 

INDUSTRIAL  PUBLISHERS,   BOOKSELLERS  AND  IMPORTERS 

810  Walnut  Street,  Philadelphia. 


ST"  Any  ot  the   Books  comprised  in   this  Catalogue  will  be  sent  by  mail, 
free  of  postage,  to  any  address  in  the  world,  at  the  publication  prices. 

'  A    Descriptive    Catalogue,  94    pages,  8vo,   will   be  sent  free  and  free 
of  postage,  to  any  one  in  any  part  of  the  world,  who   will   furnish   his 
address. 

®~  "Where    not    otherwise    stated,    all    ot    the  Books  in   this  Catalogue 
are  bound  in  muslin. 


AMATEUR  MECHANICS'  WORKSHOP: 

A  treatise  containing  plain  and  concise  direction  for  the 
manipulation  of  Wood  and  Metals,  including  Casting,  Forg- 
ing, Brazing,  Soldering  and  Carpentry.  By  the  author  of 
the  "Lathe  and  Its  Uses."  Ninth  edition.  Illustrated. 
8vo $1.50 

ARLOT.— A  Complete  Guide  for  Coach  Painters: 

Translated  from  the  French  of  M.  ARLOT,  Coach  Painter,  for 
eleven  years  Foreman  of  Painting  to  M.  Eherler,  Coach 
Maker,  Paris  By  A.  A.  FESQUET,  Chemist  and  Engineer. 
To  which  is  added  an  Appendix,  containing  Information  re- 
specting the  Materials  and  the  Practice  of  Coach  and  Car 
Painting  and  Varnishing  in  the  United  States  and  Great 
Britain  12mo $1.25 

1 


2        HENRY  CAREY  BAIRD  &  GO'S.  CATALOGUE 

ARMENGAUD,  AMOROUX,  AND  JOHNSON.— The  Prac- 
tical Draughtsman's  Book  of  Industrial  Design,  and 
Machinist's  and  Engineer's  Drawing  Companion: 

Forming  a  Complete  Course  of  Mechanical  Engineering  and 
Architectural  Drawing.  From  the  French  of  M.  Armengaud 
the  elder,  Prof,  of  Design  in  the  Conservatoire  of  Arts  and 
Industry,  Paris,  and  M.  Armengaud  the  younger,  and  Amo- 
roux,  Civil  Engineers.  Rewritten  and  arranged  with  addi- 
tional matter  and  plates,  selections  from  and  examples  of 
the  most  useful  and  generally  employed  mechanism  of  the 
day.  By  WILLIAM  JOHNSON,  Assoc.  Inst.  C.  E.  Illustrated 
by  fifty  folio  steel  plates,  and  fifty  wood-cuts.  A  new  edi- 
tion, 4to.,  cloth $5.00 

ARROWSMITH. — The  Paper-Hanger's  Companion 

Comprising  Tools,  Pastes,  Preparatory  Work;  Selection  and 
Hanging  of  Wail-Papers;  Distemper  Painting  and  Cornice- 
Tinting;  Stencil  Work;  Replacing  Sash-Cord  and  Broken 
Window  Panes;  and  Useful  Wrinkles  and  Receipts.  By 
JAMES  ARROWSMITH.  A  New,  Thoroughly  Revised,  and 
Much  Enlarged  Edition.  Illustrated  by  25  engravings,  162 
pages.  (1905) $1.00 

ASHTON.— The  Theory  and  Practice  of  the  Art  of  Design- 
ing Fancy  Cotton  and  Woolen  Cloths  from  Sample: 

Giving  full  instructions  for  reducing  drafts,  as  well  as  the 
methods  of  spooling  and  making  put  harness  for  cross  drafts 
and  finding  any  required  reed;  with  calculations  and  tables 
of  yarn.  By  FREDERIC  T.  ASHTON,  Designer,  West  Pittsfield, 
Mass.  With  fifty-two  illustrations.  One  vol.  folio $4.00 

ASKINSON.— Perfumes  and  Cosmetics: 

A  Comprehensive  Treatise  on  Perfumery,  containing  Com- 
plete Directions  for  Making  Handkerchief  Perfumes,  Smelling- 
Salts,  Sachets,  Fumigating  Pastils;  Preparations  for  the  Care 
of  the  Skin,  the  Mouth,  the  Hair;  Cosmetics,  Hair  Dyes,  and 
other  Toilet  Articles.  By  G.  W.  ASKINSON.  Translated 
from  the  German.  Revised  by  W,  L.  DUDLEY.  32  illustra- 
tions. 8vo $5.00 

BAIRD. — The  American  Cotton  Spinner,  and  Manager's 
and  Carder's  Guide: 

A  Practical  Treatise  on  Cotton  Spinning;  giving  the  Dimen- 
sions and  Speed  of  Machinery,  Draught  and  Twist  Calcula- 
tions, etc;  with  notices  of  recent  Improvements;  together 
with  Rules  and  Examples  for  making  changes  in  the  size  and 
numbers  of  Roving  and  Yarn.  Compiled  from  the  papers 
of  the  late  ROBERT  H.  BAIRD.  256  pp.,  12mo $1.50 


HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE       3 

BEANS. — A  Treatise  on  Railway  Curves  and  Location  of 
Railroads : 

By  E.  W.  BEANS,  C.  E.    Illustrated.      12mo.    Morocco  $1.00 
BELL. — Carpentry  Made  Easy: 

Or,  The  Science  and  Art  of  Framing  on  a  New  and  Improved 
System.  With  Specific  Instructions  for  Building  Balloon 
Frames,  Barn  Frames,  Mill  Frames,  Warehouses,  Church 
Spires,  etc.  Comprising  also  a  System  of  Bridge  Building, 
with  Bills,  Estimates  of  Cost,  and  valuable  Tables.  Illus- 
trated by  forty- four  plates,  comprising  nearly  200  figures. 
By  WILLIAM  E.  BELL,  Architect  and  Practical  Builder. 
8vo $5.00 

BERSCH. — Cellulose,    Cellulose    Products,    and    Rubber 

Substitutes: 

Comprising  the  Preparation  of  Cellulose,  Parchment-Cellu- 
lose, Methods  of  Obtaining  Sugar,  Alcohol,  and  Oxalic  Acid 
from  Wood-Cellulose;  Production  of  Nitro-Cellulose  and  Cellu- 
lose Esters;  Manufacture  of  Artificial  Silk,  Viscose,  Celluloid, 
Rubber  Substitutes,  Oil-Rubber,  and  Faktis.  By  Dr.  JOSEPH 
BERSCH.  Translated  by  WILLIAM  T.  BRANNT.  41  Illustra- 
tions. (1904) $3.00 

BILLINGS.— Tobacco : 

Its  History,  Variety,  Culture,  Manufacture,  Commerce,  and 
Various  Modes  of  Use.  By  E.  R.  BILLINGS.  Illustrated  by 
nearly  200  engravings.  8vo $3.00 

BIRD. — The  American  Practical  Dyers'  Companion: 

Comprising  a  Description  of  the  Principal  Dye-Stuffs  and 
Chemicals  used  in  Dyeing,  their  Nature  and  Uses;  Mordants 
and  How  Made;  with  the  best  American,  English,  French 
and  German  processes  for  Bleaching  and  Dyeing  Silk,  Wool, 
Cotton,  Linen.  Flannel,  Felt,  Dress  Goods,  Mixed  and 
Hosiery  Yarns,  Feathers,  Grass,  Felt,  Fur,  Wool,  and 
Straw  Hats,  Jute  Yarn,  Vegetable  Ivory,  Mats,  Skins,  Furs, 
Leather,  €tc.,  etc.,  by  Wood,  Aniline,  and  other  Processes, 
together  with  Remarks  on  Finishing  Agents,  and  Instructions 
in  the  Finishing  of  Fabrics,  Substitutes  for  Indigo,  Water- 
Proofing  of  Materials,  Tests  and  Purification  of  Water. 
Manufacture  of  Aniline  and  other  New  Dye  Wares,  Harmoniz- 
ing Colors,  etc.,  etc.,;  embracing  in  all  over  800  Receipts  for 
Colors  and  Shades,  accompanied  by  170  Dyed  Samples  of  Raw 
Materials  and  Fabrics.  By  F.  J.  BIRD,  Practical  Dyer, 
Author  of  "The  Dyers'  Hand-Book. "  8vo $4.00 

BLINN.— A    Practical    Workshop    Companion    for    Tin, 
Sheet- Iron,  and  Copper-plate  Workers: 

Containing  Rules  for  describing  various  kinds  of  Patterns 


4       HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE 

used  by  Tin,  Sheet-Iron  and  Copper-plate  Workers;  Practical 
Geometry;  Mensuration  of  Surface  and  Solids;  Tables  of  the 
Weights  of  Metals,  Lead-pipe,  etc.;  Tables  of  Areas  and 
Circumferences  of  Circles;  Japan,  Varnishes,  Lacquers,  Ce- 
ments, Compositions,  etc.,  etc.  By  LEROY  J.  BLINN,  Master 
Mechanic.  With  One  Hundred  and  Seventy  Illustrations. 
12mo $2.50 

BOOTH.— Marble  Worker's  Manual: 

Containing  Practical  Information  respecting  Marbles  in 
general,  their  Cutting,  Working  and  Polishing;  Veneering  of 
Marble;  Mosaics;  Composition  and  Use  of  Artificial  Marble, 
Stuccos,  Cements,  Receipts,  Secrets,  etc.,  etc.  Translated 
from  the  French  by  M.  L.  BOOTH.  With  an  Appendix  con- 
cerning American  Marbles.  12mo.,  cloth  $1.50 

BRANNT. — A  Practical  Treatise  on  Animal  and  Vegetable 
Fats  and  Oils: 

Comprising  both  Fixed  and  Volatile  Oils,  their  Physical  and 
Chemical  Properties  and  Uses,  the  Manner  of  Extracting  and 
Refining  them,  and  Practical  Rules  for  Testing  them;  as  well 
as  the  Manufacture  of  Artificial  Butter  and  Lubricants,  etc., 
with  lists  of  American  Patents  relating  to  the  Extraction, 
Rendering,  Refining,  Decomposing  and  Bleaching  of  Fats 
and  Oils.  By  WILLIAM  T.  BRANNT,  Editor  of  the  "Techno- 
Chemical  Receipt  Book."  Second  Edition,  Revised  and 
in  great  part  Rewritten.  Illustrated  by  302  Engravings. 
In  Two  Volumes.  1304  pp.  8vo $10.00 

BRANNT. — A  Practical  Treatise  on  Distillation  and  Rec- 
tification of  Alcohol: 

Comprising  Raw  Materials;  Production  of  Malt,  Preparation 
of  Mashes  and  of  Yeast;  Fermentation;  Distillation  and 
Rectification  and  Purification  of  Alcohol;  Preparation  of 
Alcoholic  Liquors,  Liqueurs,  Cordials,  Bitters,  Fruit  Essences, 
Vinegar,  etc.;  Examination  of  Materials  for  the  Preparation 
of  Malt  as  well  as  of  the  Malt  itself;  Examination  of  Mashes 
before  and  after  Fermentation;  Alcoholometry,  with  Numer- 
ous Comprehensive  Tables;  and  an  Appendix  on  the  Manu- 
facture of  Compressed  Yeast  and  the  Examination  of  Alcohol 
and  Alcoholic  Liquors  for  Fusel  Oil  and  other  Impurities. 
By  WILLIAM  T.  BRANNT,  Editor  of  "The  Techno-Chemical 
Receipt  Book."  Second  Edition.  Entirely  Rewritten.  Il- 
lustrated by  105  engravings.  460  pages.  8vo.  (Dec., 
1903) $10.00 

BRANNT.— India  Rubber,  Gutta-Percha  and  Balata: 

Occurrence,  Geographical  Distribution,  and  Cultivation,  Ob- 
taining and  Preparing  the  Raw  Materials,  Modes  of  Working 


HENRY  CAREY  BAIRD  &  CQ.'S  CATALOGUE       5 

and  Utilizing  them,  including  Washing,  Maceration,  Mixing, 
Vulcanizing,  Rubber  and  Gutta-Percha  Compounds,  Utiliza- 
tion of  Waste,  etc.  By  WILLIAM  T.  BRANNT.  Illustrated. 
12mo.  A  new  edition  in  preparation. 

BRANNT. — A  Practical  Treatise  on  the  Manufacture  of 
Vinegar  and  Acetates,  Cider,  and  Fruit-Wines: 

Preservation  of  Fruits  and  Vegetables  by  Canning  and  Evap- 
oration; Preparation  of  Fruit-Butters,  Jellies,  Marmalades, 
Catchups,  Pickles,  Mustards,  etc.  Edited  from  various 
sources.  By  WILLIAM  T.  BRANNT.  Illustrated  by  101  En- 
gravings. 575  pp.  8vo;  3d  edition Net,  $6.00 

BRANNT.— The  Metallic  Alloys:  A  Practical  Guide: 

For  the  Manufacture  of  all  kinds  of  Alloys,  Amalgams,  and 
Solders,  used  by  Metal  Workers:  together  with  their  Chem- 
ical and  Physical  Properties  and  their  Application  in  the  Arts 
and  the  Industries;  with  an  Appendix  on  the  Coloring  of 
Alloys  and  the  Recovery  of  Waste  Metals.  By  WILLIAM 
T.  BRANNT.  45  Engravings.  Third,  Revised,  and  Enlarged 
Edition.  570  pages.  8vo Net,  $5.00 

BRANNT.— The  Metal  Worker's  Handy-Book  of  Receipts 
and  Processes: 

Being  a  Collection  of  Chemical  Formulas  and  Practical 
Manipulations  for  the  working  of  all  Metals;  including  the 
decoration  and  Beautifying  of  Articles  Manufactured  there- 
from, as  well  as  their  Preservation.  Edited  from  various 
sources.  By  WILLIAM  T.  BRANNT.  Illustrated.  '  12mo.$2.50 

BRANNT. — Petroleum : 

Its  History,  Origin,  Occurrence,  Production,  Physical  and 
Chemical  Constitution,  Technology,  Examination  and  Uses; 
Together  with  the  Occurrence  and  Uses  of  Natural  Gas. 
Edited  chiefly  from  the  German  of  Prof.  Hans  Hoefer  and  Dr. 
Alexander  Veith  by  Wm.  T.  BRANNT.  Illustrated  by  3 
Plates  and  284  Engravings.  743  pp.  8vo .. .  .$12.50 

BRANNT.— The    Practical    Dry     Cleaner,     Scourer    and 
Garment  Dyer: 

Comprising  Dry,  Chemical,  or  French  Cleaning;  Purifica- 
tion of  Benzine;  Removal  of  Stains,  or  Spotting;  Wet  Clean- 
ing; Finishing  Cleaned  .Fabrics;  Cleaning  and  Dyeing  Furs, 
Skin  Rugs  and  Mats:  Cleaning  and  Dyeing  Feathers;  Clean- 
ing and  Renovating  Felt,  Straw  and  Panama  Hats;  Bleach- 
ing and  Dyeing  Straw  and  Straw  Hats;  Cleaning  and  Dyeing 
Gloves;  Garment  Dyeing;  Stripping;  Analysis  of  Textile 
Fabrics.  Edited  by  WILLIAM  T.  BRANNT,  Editor  of  "The 
Techno-Chemical  Receipt  Book."  Fourth  Edition,  Revised 


6       HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE 

and  Enlarged.  Illustrated  by  Forty-One  Engravings.  12 
mo.  371  pp .' $2.50 

CONTENTS  :  I.  Dry  Chemical  or  French  Cleaning.  II.  Removal 
of  Stains  or  Spotting.  III.  Wet  Washing.  IV.  Finishing  Cleaned 
Fabrics.  V.  Cleaning  and  Dyeing  Furs,  Skin  Rugs  and  Mats.  VI. 
Cleaning  and  Dyeing  Feathers.  VII.  Cleaning  and  Renovating  Felt, 
Straw  and  Panama  Hats  ;  Bleaching  and  Dyeing  Straw  and  Straw 
Hats.  VIII.  Cleaning  and  Dyeing  Gloves.  IX.  Garment  Dyeing. 
X.  Stripping  Colors  from  Garments  and  Fabrics.  XI.  Analysis  of 
Textile  Fabrics.  Index. 

BRANNT. — The  Soap  Maker's  Hand-Book  of   Materials, 

Processes  and  Receipts  for  every  description  of  Soap;  includ- 
ing Fats,  Fat  Oils  and  Fatty  Acids;  Examination  of  Fats  and 
Oils;  Alkalies;  Testing  Soda  and  Potash;  Machines  and 
Utensils;  Hard  Soaps;  Soft  Soaps;  Textile  Soaps;  Washing 
Powders  and  Allied  Products;  Toilet  Soaps,  Medicated 
Soaps,  and  Soap  Specialties;  Essential  Oils  and  other  Perfum- 
ing Materials;  Testing  Soaps.  Edited  chiefly  from  the  Ger- 
man of  DR.  C.  DEITE,  A.  ENGELHARDT,  F.  WILTNER,  and 
numerous  other  Experts.  With  Additions  by  WILLIAM  T. 
BRANNT,  Editor  of  "The  Techno-Chemical  Receipt  Book." 
Illustrated  by  Fifty-four  Engravings.  Second  edition,  Re- 
vised and  in  great  part  Re- Written.  535pp.  8vo $6.00 

BRANNT. — Varnishes,  Lacquers,  Printing  Inks  and  Seal- 
ing Waxes : 

Their  Raw  Materials  and  their  Manufacture,  to  which  is 
added  the  Art  of  Varnishing  and  Lacquering,  including  the 
Preparation  of  Putties  and  of  Stains  for  Wood,  Ivory,  Bone, 
Horn,  and  Leather.  By  WILLIAM  T.  BRANNT.  Illustrated 
by  39  Engravings,  338  pages.  12mo $3.00 

BRANNT-WAHL.— The  Techno-Chemical  Receipt  Book: 

Containing  several  thousand  Receipts  covering  the  latest, 
most  important,  and  most  useful  discoveries  in  Chemical 
Technology,  and  their  Practical  Application  in  the  Arts  and 
the  Industries.  Edited  chiefly  from  the  German  of  Drs. 
Winckler,  Eisner,  Heintze,  Mierzinski,  Jacobsen,  Roller  and 
Heinzerling,  with  additions  by  WM.  T.  BRANNT  and  WM.  H. 
WAHL,  Ph.  D.  Illustrated  by  78  engravings.  12mo.  495 
pages $2.00 

BROWN. — Five  Hundred   and   Seven  Mechanical  Move- 
ments: 

Embracing  all  those  which  are  most  important  in  Dynamics, 
Hydraulics,  Hydrostatics,  Pneumatics,  Steam  Engines,  Mill 
and  other  Gearing,  Presses,  Horology,  and  Miscellaneous 
Machinery;  and  including  many  movements  never  before 
published,  and  several  of  which  have  only  recently  come  into 
use.  By  HENRY  T.  BROWN $1.00 


HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE        7 

BULLOCK.— The  Rudiments  of  Architecture  and  Build- 
ing: 

For  the  use  of  Architects,  Builders,  Draughtsmen,  Machin- 
ists, Engineers  and  Mechanics.  Edited  by  JOHN  BULLOCK, 
author  of  "The  American  Cottage  Builder."  Illustrated 
by  250  Engravings.  8vo $2.50 

BYRNE. — Hand-Book    for    the    Artisan,    Mechanic,    and 
Engineer: 

Comprising  the  Grinding  and  Sharpening  of  Cutting  Tools, 
Abrasive  Processes,  Lapidary  Work,  Gem  and  Glass  En- 
graving, Varnishing  and  Lacquering,  Apparatus,  Materials 
and  Processes  for  Grinding  and  Polishing,  etc.  By  OLIVER 
BYRNE.  Illustrated  by  185  wood  engravings.  8vo ....  $4.00 

BYRNE.— Pocket-Book  for  Railroad  and  Civil  Engineers: 

Containing  New,  Exact  and  Concise  Methods  for  Laying  out 
Railroad  Curves,  Switches,  Frog  Angles  and  Crossings;  the 
Staking  out  of  work;  Levelling;  the  Calculation  of  Cuttings; 
Embankments;  Earthwork,  etc.  By  OLIVER  BYRNE.  18mo., 
full  bound,  pocketbook  form. $1.50 

BYRNE.— The  Practical  Metal- Worker's  Assistant: 

Comprising  Metallurgic  Chemistry;  the  Arts  of  Working  all 
Metals  and  Alloys;  Forging  of  Iron  and  Steel;  Hardening  and 
Tempering;  Melting  and  Mixing;  Casting  and  Founding; 
Works  in  Sheet  Metals;  the  Process  Dependent  on  the  Duc- 
tility of  the  Metals;  Soldering;  etc.  By  JOHN  PERCY.  The 
Manufacture  of  Malleable  Iron  Castings,  and  Improvements 
in  Bessemer  Steel.  By  A.  A.  FESQUET,  Chemist  and  En- 
gineer. With  over  Six  Hundred  Engravings,  Illustrating 
every  Branch  of  the  Subject.  8vo $3.50 

CABINET    MAKER'S    ALBUM    OF    FURNITURE: 

Comprising  a  Collection  of  Designs  for  various  Styles  of 
Furniture.  Illustrated  by  Forty-eight  Large  and  Beauti- 
fully Engraved  Plates.  Oblong,  8vo 

CALLINGHAM.— Sign  Writing  and  Glass  Embossing: 
A  complete  Practical  Illustrated  Manual  of  the  Art.    By 
JAMES  CALLINGHAM.    To  which  are  added  Numerous  Alpha- 
bets and  the  Art  of  Letter  Painting  Made  Easy.    By  JAMES 
C.   BADENOCH.    258  pages.    12mo c $1.50 

CAREY.— A   Memoir   of   Henry   C.    Carey: 
By  DR.  WM.  ELDER.    With  a  portrait.    8vo.,  cloth 75 

CAREY.— The  Works  of  Henry  C.  Carey: 
Manual    of    Social    Science.     Condensed    from    Carey's 
"Principles  of  Social  Science."    By  KATE  McKEAN    1  vol. 
12mo ..$2.00 


8        HENRY  CARiY  BAIRD  &  CO.'S  CATALOGUE 

Miscellaneous  Works.    With  a  Portrait.  2  vols.  8vo.  $10.00 

Past,  .Present  and  Future.     8vo $2.50 

Principles  of  Social  Science.     3  volumes,  8vo $10.00 

The  Slave-Trade,  Domestic  and  Foreign;    Why  it  Exists, 

and  How  it  may  be  Extinguished  (1853).    8vo $2.00 

The  Unity  of  Law:  As  Exhibited  in  the  Relations  of  Phys- 
ical, Social,  Mental  and  Moral  Science  (1872).  8vo $2.50 

COOLEY. — A  Complete  Practical  Treatise  on  Perfumery: 

Being  a  Hand-book  of  Perfumes,  Cosmetics  and  other  Toilet 
Articles,  with  a  Comprehensive  Collection  of  Formulae.  By 
ARNOLD  COOLEY.  12mo $1.00 

COURTNEY.— The  Boiler  Maker's  Assistant  in  Drawing, 
Templating,  and  Calculating  Boiler  Work  and  Tank 
Work,  etc. 

Revised  by  D.  K.  CLARK.     102  ills.    Fifth  edition 80 

COURTNEY.— The  Boiler  Maker's  Ready  Reckoner: 

With  Examples  of  Practical  Geometry  and  Templating.  Re- 
vised by  D.  K.  CLARK,  C.  E.  37  illustrations.  Fifth  edi- 
tion  $1.60 

CRISTIANI.— A  Technical  Treatise  on  Soap  and  Candles: 

With  a  Glance  at  the  Industry  of  Fats  and  Oils.  By  R.  S. 
Cristiani,  Chemist.  Author  of  "Perfumery  and  Kindred 
Arts."  Illustrated  by  176  Engravings.  581  pages,  8vo 

$15.00 

CROSS.— The  Cotton  Yarn  Spinner: 
Showing  how  the  Preparation  should  be  arranged  for  Differ- 
ent Counts  of  Yarns  by  a  System  more  uniform  than  has  hith- 
erto been  practiced;  by  having  a  Standard  Schedule  from 
which  we  make  all  our  Changes.  By  RICHARD  CROSS.  122 
pp.  12mo 75 

DAVIDSON. — A  Practical  Manual  of  House  Painting, 
Graining,  Marbling,  and  Sign-Writing: 

Containing  full  information  on  the  processes  of  House  Paint- 
ing in  Oil  and  Distemper,  the  Formation  of  Letters  and 
Practice  of  Sign- Writing,  the  Principles  of  Decorative  Art, 
a  Course  of  Elementary  Drawing  for  House  Painters,  Writers, 
etc.,  and  a  Collection  of  Useful  Receipts.  With  nine  colored 
illustrations  of  Woods  and  Marbles,  and  numerous  wood  en- 
gravings. By  ELLIS  A.  DAVIDSON.  12mo $2.00 

DAVIES.— A  Treatise  on  Earthy  and  Other  Minerals  and 
Mining: 

By  D.  C.  DAVIES.  F.  G.  S.,  Mining  Engineer,  etc.  Illustrated 
by  76  Engravings.  12mo $5.00 


HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE       9 

DA  VIES  .—A    Treatise    on    Metalliferous    Minerals    and 
Mining: 

By  D.  C.  DAVIES,  F.  G.  S.,  Mining  Engineer,  Examiner  of 
Mines,  Quarries  and  Collieries.  Illustrated  by  148  engrav- 
ings of  Geological  Formations,  Mining  Operations  and  Ma- 
chinery, drawn  from  the  practice  of  all  parts  of  the  world. 
Fifth  Edition,  thoroughly  Revised  and  much  Enlarged  by 
his  son,  E.  Henry  Davies.  12mo.  524  pages . .  .$5.00 

DAVIS. — A    Practical   Treatise   on    the   Manufacture   of 
Brick,  Tiles  and  Terra-Gotta: 

Including  Stiff  Clay,  Dry  Clay,  Hand  Made,  Pressed  or 
Front,  and  Roadway  Paving  Brick,  Enamelled  Brick,  with 
Glazes  and  Colors,  Fire  Brick  and  Blocks,  Silica  Brick,  Carbon 
Brick,  Glass  Pots,  Retorts,  Architectural  Terra-Cotta,  Sewer 
Pipe,  Drain  Tile,  Glazed  and  Unglazed  Roofing  Tile,  Art  Tile, 
Mosaics,  and  Imitation  of  Intrarsia  or  Inlaid  Surfaces.  Com- 
prising every  product  of  Clay  employed  in  Architecture,  En- 
gineering, and  the  Blast  Furnace.  With  a  Detailed  Descrip- 
tion of  the  Different  Clays  employed,  the  Most  Modern  Ma- 
chinery, Tools,  and  Kilns  used,  and  the  Processes  for  Handling 
Disintegrating,  Tempering,  and  Moulding  the  Clay  into  Shape, 
Drying,  Setting,  and  Burning.  By  CHARLES  THOMAS  DAVIS. 
Third  Edition.  Revised  and  in  great  part  rewritten.  Il- 
lustrated by  261  engravings.  662  pages ..  (Scarce.) 

DAVIS.— The  Manufacture  of  Paper: 

Being  a  Description  9f  the  various  Processes  for  the  Fabrica- 
tion, Coloring  and  Finishing  of  every  kind  of  Paper,  Includ- 
ing the  Different  Raw  Materials  and  the  Methods  for  De- 
termining their  Values,  the  Tools,  Machines  and  Practical 
Details  connected  with  an  intelligent  and  a  profitable  prose- 
cution of  the  art,  with  special  reference  to  the  best  American 
Practice.  To  which  are  added  a  History  of  Paper,  complete 
Lists  of  Paper-Making  Materials,  List  of  American  Machines, 
Tools  and  Processes  used  in  treating  the  Raw  Materials,  and 
in  Making,  Coloring  and  Finishing  Paper.  By  CHARLES  T. 
DAVIS.  Illustrated  by  156  Engravings.  608  pages.  8vo .  $6.00 

DAWIDOWSKY-BRANNT.— A  Practical  Treatise  on  the 
Raw  Materials  and  Fabrication  of  Glue,  Gelatine, 
Gelatine  Veneers  and  Foils,  Isinglass,  Cements, 
Pastes,  Mucilages,  etc.: 

Based  upon  Actual  Experience.  By  F.  DAWIDOWSKY,  Tech- 
nical Chemist.  Translated  from  the  German,  with  extensive 
additions,  including  a  description  of  the  most  Recent  Ameri- 
can Processes,  by  WILLIAM  T.  BRANNT.  2d  revised  edition, 
350  pages.  (1905)  Price $3.00 


10     HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE 

DEITE. — A   Practical   Treatise   on    the   Manufacture   of 
Perfumery : 

Comprising  directions  for  making  all  kinds  of  Perfumes, 
Sachet  Powders,  Fumigating  Materials,  Dentrifices,  Cos- 
metics, etc.,  with  a  full  account  of  the  Volatile  Oils,  Balsams, 
Resins,  and  other  Natural  and  Artificial  Perfume-substances, 
including  the  Manufacture  of  Fruit  Ethers,  and  tests  of  their 
purity.  By  DR.  C.  DEITE,  assisted  by  L.  BORCHERT,  F. 
EICHBAUM,  E.  KUGLER,  H.  TOEFFNER,  and  other  experts. 
From  the  German,  by  WM.  T.  BRANNT.  28  Engravings. 
358  pages.  8vo $3.00 

DE  KONINCK-DIETZ.— A  Practical  Manual  of  Chemical 
Analysis  and  Assaying: 

As  applied  to  the  Manufacture  of  Iron  from  its  Ores,  and  to 
Cast  Iron,  Wrought  Iron,  and  Steel,  as  found  in  Commerce. 
By  L.  L.  DEKONINCK,  Dr.  Sc.,  and  E.  DIETZ,  Engineer.  Ed- 
ited with  Notes,  by  ROBERT  MALLET,  F.  R.  S.,  F.  S.  G.,  M. 
I.  C.  E.,  etc.  American  Edition,  Edited  with  Notes  and  an 
Appendix  on  Iron  Ores,  by  A.  A.  FESQUET,  Chemist  and 
Engineer.  12mo $1.00 

DIETERICHS. — A    Treatise    on    Friction,     Lubrication, 
Oils  and  Fats: 

The  Manufacture  of  Lubricating  Oils,  Paint  Oils,  and  of 
Grease,  and  the  Testing  of  Oils.  By  E.  F.  DIETERICHS, 
Member  of  the  Franklin  Institute;  Member  National  Associa- 
tion of  Stationary  Engineers;  Inventor  of  Dietrichs'  Valve- 
Oleum  Lubricating  Oils.  Second  Edition  Revised.  12mo. 
A  practical  book  by  a  practical  man $1.25 

DUNCAN. — Practical  Surveyor's  Guide: 

Containing  the  necessary  information  to  make  any  person  of 
common  capacity,  a  finished  land  surveyor,  without  the  aid 
of  a  teacher.  By  ANDREW  DUNCAN.  Revised.  72  Engrav- 
ings. 214  pp.  12mo $1.50 

DUPLAIS. — A   Treatise   on    the   Manufacture   and    Dis- 
tillation of  Alcoholic  Liquors: 

Comprising  Accurate  and  Complete  Details  in  Regard  to 
Alcohol  from  Wine,  Molasses,  Beets,  Grain,  Rice,  Potatoes, 
Sorghum,  Asphodel,  Fruits,  etc.;  with  the  Distillation  and 
Rectification  of  Brandy,  Whiskey,  Rum,  Gin,  Swiss  Absinthe, 
etc.,  the  Preparation  of  Aromatic  Waters,  Volatile  Oils  or 
Essences,  Sugars,  Syrups,  Aromatic  Tinctures,  Liqueurs, 
Cordial  Wines,  Effervescing  Wines,  etc.,  the  Ageing  of  Brandy 
and  the  Improvement  of  Spirits,  with  Copious  Directions 
and  Tables  for  Testing  and  Reducing  Spirituous  Liquors,  etc., 


HENRY  CAR2Y  BAIRD  &  CO.'S  CATALOGUE      11 

etc.  Translated  and  Edited  from  the  French  of  MM.  Du- 
PLAIS.  By  M.  McKENNiE,  M.  D.  Illustrated.  743  pp. 
8vo $15.00 

EDWARDS. — A  Catechism  of  the  Marine  Steam-Engine: 

For  the  use  of  Engineers,  Firemen,  and  Mechanics.  A  Prac- 
tical Work  for  Practical  Men.  By  EMORY  EDWARDS,  Me- 
chanical Engineer.  Illustrated  by  sixty-three  Engravings, 
including  examples  of  the  most  modern  Engines.  Third 
edition,  thoroughly  revised,  with  much  additional  matter. 
12mo.  414  pages $1.50 

EDWARDS. — American     Marine     Engineer,     Theoretical 
and   Practical: 

With  Examples  of  the  latest  and  most  approved  American 
Practice.  By  EMORY  EDWARDS.  85  Illustrations.  12mo.  $1.50 

EDWARDS. — Modern  American  Locomotive  Engines: 

Their  Design,  Construction  and  Management.  By  EMORY 
EDWARDS.  Illustrated.  12mo $1.50 

EDWARDS.— Modern  American  Marine  Engines,  Boilers, 
and  Screw  Propellers: 

Their  Design  and  Construction.     146  pp.    4to $2.00 

EDWARDS. — 900    Examination   Questions   and   Answers: 

For  Engineers  and  Firemen  (Land  and  Marine)  who  desire 
to  obtain  a  United  States  Government  or  State  License. 
Pocket-book  form,  gilt  edge $1.50 

EDWARDS.— The  American  Steam  Engineer: 

Theoretical  and  Practical,  with  examples  of  the  latest  and 
most  approved  American  practice  in  the  design  and  con- 
struction of  Steam  Engines  and  Boilers.  For  the  use  of 
Engineers,  machinists,  boiler-makers,  and  engineering  stu- 
dents. By  EMORY  EDWARDS.  Fully  illustrated.  419  pages. 
12mo $1.50 

EDWARDS.— The  Practical  Steam  Engineer's  Guide: 

In  the  Design,  Construction,  and  Management  of  American 
Stationary,  Portable,  and  Steam  Fire-Engines,  Steam  Pumps, 
Boilers,  Injectors,  Governors,  Indicators,  Pistons  and  Rings, 
Safety  Valves  and  Steam  Gauges.  For  the  use  of  Engineers, 
Firemen,  and  Steam  Users.  By  EMORY  EDWARDS.  Illus- 
trated by  119  engravings.  420  pages.  12mo $2.00 

ELDER. — Conversations    on    the    Principal    Subjects    of 
Political  Economy: 

By  DR.  WILLIAM  ELDER.    8vo $1.50 


12      HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE 

ELDER. — Questions  of  the  Day: 

Economic  and  Social.    By  DR.  WILLIAM  ELDER,    8vo..$3.00 

ERNI  AND  BROWN.— Mineralogy  Simplified: 

Easy  Methods  of  Identifying  Minerals,  including  Ores,  by 
Means  of  the  Blow-pipe,  by  Flame  Reactions,  by  Humid 
Chemical  Analysis,  and  by  Physical  Tests.  By  HENRI 
ERNI,  A.  M.,  M.  D.  Fourth  Edition,  revised,  re-arranged 
and  with  the  addition  of  entirely  new  matter,  including  Tables 
for  the  Determination  of  Minerals  by  Chemicals  and  Pyrog- 
nostic  Characters,  and  by  Physical  Characters.  By  AMOS 
P.  BROWN,  A.  M.,  Ph.  D.  464  pp.  Illustrated  by  123  En- 
gravings, pocket-book  form-,  full  flexible  morocco,  gilt  edges. 

$2.50 

FAIRBAIRN.— The  Principles  of  Mechanism  and  Machi- 
nery of  Transmission: 

Comprising  the  Principles  of  Mechanism,  Wheels,  and  Pul- 
leys, Strength  and  Proportion  of  Shafts,  Coupling  of  Shafts, 
and  Engaging  and  Disengaging  Gear.  By  SIR  WILLIAM 
FAIRBAIRN,  Bart.,  C  E.  Beautifully  illustrated  by  over  150 
wood-cuts.  In  one  volume.  12mo $2.00 

FLEMING. — Narrow  Gauge  Railways  in  America: 

A  Sketch  of  their  Rise,  Progress,  and  Success.  Valuable 
Statistics  as  to  Grades,  Curves,  Weight  of  Rail,  Locomotives, 
Cars,  etc.  By  HOWARD  FLEMING.  Illustrated.  8vo.  .$1.00 

FLEMMING.— Practical  Tanning: 

A  Handbook  of  Modern  Processes,  Receipts,  and  Sugges- 
tions for  the  Treatment  of  Hides,  Skins,  and  Pelts  of  Every 
Description.  By  LEWIS  A.  FLEMMING,  American  Tanner. 
Third  Edition  Revised  and  in  great  part  rewritten,  over  600 
pp.  8vo  1916 $6.00 

FORSYTH. — Book  of  Designs  for  Headstones,  Mural,  and 

other  Monuments: 

Containing  78  Designs.  By  JAMES  FORSYTH,  With  an  In- 
troduction by  CHARLES  BOUTELL,  M.  A.  4to.  Cloth.  .$3.00 

GARDNER.— Everybody's  Paint  Book: 
A  Complete  Guide  to  the  Art  of  Outdoor  and  Indoor  Paint- 
ing    38  Illustrations.     12mo.     183  pp $1.00 

GARDNER. — The  Painter's  Encyclopedia: 
Containing  Definitions  of  all  Important  Words  in  the  Art  of 
Plain  and  Artistic  Painting,  with  Details  of  Practice  in  Coach, 
Carriage,  Railway  Car,  House,  Signe  and  Ornamental  Paint- 
ing, including  Graining,  Marbling,  Staining,  Varnishing, 
Polishing,  Lettering,  Stenciling,  Gilding,  Bronzing,  etc.  By 
FRANKLIN  B.  GARDNER  158  illustrations.  12mo.  427  pp 

$2.00 


HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE      13 

GEE. — The  Goldsmith's  Handbook: 

Containing  full  instructions  for  the  Alloying  and  Working  of 
Gold,  including  the  Art  of  Alloying,  Melting,  Reducing,  Color- 
ing, Collecting,  and  Refining;  the  Processes  of  Manipulation, 
Recovery  of  Waste;  Chemical  and  Physical  Properties  of 
Gold;  with  a  New  System  of  Mixing  its  Alloys;  Solders,  En- 
amels; and  other  Useful  Rules  and  Recipes.  By  GEORGE  E. 

GEE.     12mo. $1.25 

GEE. — The  Jeweler's  Assistant  in  the  Art  of  Working  in 

Gold: 
A  Practical  Treatise  for  Masters  and  Workmen.  12mo   $3.00 

GEE. — The  Silversmith's  Handbook: 

Containing  full  instructions  for  the  Alloying  and  Working  of 
Silver,  including  the  different  modes  of  Refining  and  Melting 
the  Metal;  its  Solders;  the  Preparation  of  Imitation  Altoys; 
Methods  of  Manipulation;  Prevention  of  Waste;  Instructions 
for  Improving  and  Finishing  the  Surface  of  the  Work;  together 
with  other  Useful  Information  and  Memoranda.  By  GEORGE 
E.  GEE.  Illustrated.  12mo $1.25 

GOTHIC   ALBUM    FOR   CABINET-MAKERS: 

Designs  for  Gothic  Furniture  Twenty-three  plates.  Ob- 
long   $1.00 

GRANT.— A   Handbook  on   the  Teeth  of   Gears: 
Their  Curves,   Properties,  and  Practical  Construction     By 
GEORGE  B.  GRANT     Illustrated.    Third  Edition,  enlarged. 
8vo $1.00 

GREGORY.— Mathematics  for  Practical  Men: 
Adapted  to  the  Pursuits  of  Surveyors,  Architects,  Mechan- 
ics,  and  Civil  Engineers.    By  OLINTHUS  GREGORY.    8vo., 
plates \ $3.00 

GRISWOLD. — Railroad    Engineer's    Pocket    Companion 

for  the  Field:  • 
Comprising  Rules  for  Calculating  Deflection  Distances  and 
Angles,  Tangential  Distances  and  Angles  and  all  Necessary 
Tables  for  Engineers;  also  the  Art  of  Levelling  from  Prelim- 
inary Survey  to  the  Construction  of  Railroads,  intended 
Expressly  for  the  Young  Engineer,  together  with  Numerous 
Valuable  Rules  and  Examples.  By  W.  GRISWOLD  12mo 
Pocketbook  form $1.50 

GRUNER.— Studies    of    Blast    Furnace   Phenomena: 
By  M.  L.  GRUNER,  President  of  the  General  Council  of  Mines 
of  France,  and  lately  Professor  of  Metallurgy  at  the  Ecole 
des  Mines.    Translated,  with  the  author's  sanction,  with  an 
Appendix,  by  L.  D.  B.  GORDON,  F  R.  S.  E.,  F.  G.  S.    8vo. 

$2.50 


14      HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE 

Hand-Book  of  Useful  Tables  for  the  Lumberman,  Farmer 
and  Mechanic: 

Containing  Accurate  Tables  of  Logs  Reduced  to  Inch  Board 
Measure,  Plank,  Scantling  and  Timber  Measure;  Wages  and 
Rent,  by  Week  or  Month;  Capacity  of  Granaries,  Bins  and 
Cisterns;  Land  Measure,  Interest  Tables  with  Directions 
for  finding  the  Interest  on  any  sum  at  4,  5,  6,  7  and  8  per 
cent.,  and  many  other  Useful  Tables.  32mo.,  boards.  186 
pages 25 

HASERIGK.— The   Secrets   of   the  Art   of   Dyeing   Wool, 
Cotton  and  Linen: 

Including  Bleaching  and  Coloring  Wool  and  Cotton  Hosiery 
and  Random  Yarns.  A  Treatise  based  on  Economy  and 
Practice  By  E.  C.  HASERICK.  Illustrated  by  323  Dyed 
Patterns  of  the  Yarns  or  Fabrics  8vo $4.50 

HATS  AND  FELTING: 

A  Practical  Treatise  on  their  Manufacture.  By  a  Practical 
Hatter.  Illustrated  by  Drawings  of  Machinery,  etc.  8vo. 

$1.00 
HAUPT. — A  Manual   of   Engineering   Specifications   and 

Contracts : 

By  LEWIS  M.  HAUPT,  C.  E.  Illustrated  with  numerous 
maps.  328pp.  8vo $2.00 

HAUPT. — The  Topographer,  His  Instruments  and  Meth- 
ods: 

By  LEWIS  M.  HAUPT,  A.  M.,  C.  E.  Illustrated  with  numer- 
ous plates,  maps  and  engravings.  247  pp.  8vo $2.00 

HAUPT. — Street  Railway  Motors: 

With  Descriptions  and  Cost  of  Plants  and  Operation  of  the 
various  systems  now  in  use.  12mo $1.50 

HULME. — Worfced     Examination     Questions     in     Plane 
Geometrical   Drawing: 

For  the  Use  of  Candidates  for  the  Royal  Military  Academy. 
Woolwich;  the  Royal  Military  College,  Sandhurst;  the  In- 
dian Civil  Engineering  College,  Cooper's  Hill;  Indian  Public 
Works  and  Telegraph  Department;  Royal  Marine  Light  In- 
fantry; the  Oxford  and  Cambridge  Local  Examinations,  etc. 
By  F.  EDWARD  HULME,  F.  L.  S.,  F.  S.  A.,  Art-Master  Marl- 
borough  College.  Illustrated  by  300  examples.  Small 
quarto $1.00 

KELLEY. — Speeches,  Addresses,  and  Letters  on  Industria. 
and  Financial  Questions: 

By  HON.  WILLIAM  D.  KELLEY,  M.  C.    544  pages.    8vo  $.200 


HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE      15 

KEMLO. — Watch  Repairer's  Hand-Book: 

Being  a  Complete  Guide  to  the  Young  Beginner,  in  Taking 
Apart,  Putting  Together,  %  and  Thoroughly  Cleaning  the 
English  Lever  and  other  Foreign  Watches,  and  all  American 
Watches.  By  F.  KEMLO,  Practical  Watchmaker.  With 
Illustrations.  12mo. $1.25 

KICK. — Flour  Manufacturer: 

A  Treatise  on  Milling  Science  and  Practice  By  FREDERICK 
KICK,  Imperial  Regierungsrath,  Professor  of  Mechanical 
Technology  in  the  Imperial  German  Polytechnic  Institute, 
Prague.  Translated  from  the  second  enlarged  and  revised 
edition  with  supplement  by  H.  H.  P.  POWLES,  Assoc.  Memb. 
Institution  of  Civil  Engineers.  Illustrated  with  28  Plates, 
and  167  Wood-cuts.  367  pages.  8vo $7.50 

KINGZETT.— The   History,   Products,   and   Processes   of 
the  Alkali  Trade: 

Including  the  most  Recent  Improvements.  By  CHARLES 
THOMAS  KINGZETT,  Consulting  Chemist.  With  23  illustra- 
tions. 8vo $2.00 

KIRK.— A  Practical  Treatise  on  Foundry  Irons: 

Comprising  Pig  Iron,  and  Fracture  Grading  of  Pig  and  Scrap 
Irons;  Scrap  Irons;  Mixing  Irons;  Elements  and  Metalloids"; 
Grading  Iron  by  Analysis;  Chemical  Standards  for  Iron; 
Castings;"  Testing  Cast  Iron;  Semi-Steel;  Malleable  Iron; 
Etc.,  Etc.  By  EDWARD  KIRK,  Practical  Moulder  and  Melter, 
Consulting  Expert  in  Melting.  Illustrated.  294  pages. 
8vo.  1911 $3.00 

KIRK. — The  Cupola  Furnace: 

A  Practical  Treatise  on  the  Construction  and  Management  of 
Foundry  Cupolas.  By  EDWARD  KIRK,  Practical  Moulder  and 
Melter,  Consulting  Expert  in  Melting.  Illustrated  by  106 
Engravings.  Third  Edition,  revised  and  enlarged.  482 
pages.  8vo.  1910 $3.50 

KOENIG.— Chemistry  Simplified: 

A  Course  of  Lectures  on  the  Non-Metals,  Based  upon  the 
Natural  Evolution  of  Chemistry.  Designed  Primarily  for 
Engineers.  By  GEORGE  AUGUSTUS  KOENIG,  Ph.  D.,  A.  M , 
E.  M.,  Professor  of  Chemistry,  Michigan  College  of  Mines, 
Houghton.  Illustrated  by  103  Original  Drawings.  449  pp. 
12mo.  (1906) $2.25 

LANGBEIN.— A  Complete  Treatis'e  on  the  Electro-Deposi- 
tion of  Metals: 

Comprising  Electro-Plating  and  Galvanoplastic  Operations, 
The  Deposition  of  Metals  by  the  Contract  and  Immersion 


16     HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE 

Processes,  the  Coloring  of  Metals,  the  Methods  of  Grinding 
and  Polishing,  as  well  as  the  Description  of  the  Voltaic  Cells, 
Dynamo-Electric  Machines,  Thermopiles,  and  of  the  Materi- 
als and  Processes  Used  in  Every  Department  of  the  Art. 
Translated  from  the  latest  German  Edition  of  DR.  GEORGE 
LANGBEIN,  Proprietor  of  a  Manufactory  for  Chemical  Pro- 
ducts, Machines,  Apparatus  and  Utensils  for  Electro-Platers, 
and  of  an  Electro-Plating  Establishment  in  Leipzig.  With 
Additions  by  WILLIAM  T.  BRANNT,  Editor  of  "The  Techno- 
Chemical  Receipt  Book."  Seventh  Edition,  Revised  and 
Enlarged.  Illustrated  by  163  Engravings.  8vo.  725  pages. 
1913 $5.00 

LARKIN. — The     Practical     Brass     and     Iron     Founder's 
Guide: 

A  Concise  Treatise  on  Brass  Founding,  Moulding,  the  Metals 
and  their  Alloys,  etc.;  to  which  are  added  Recent  Improve- 
ments in  the  Manufacture  of  Iron,  Steel  by  the  Bessemer 
Process,  etc.,  etc.  By  JAMES  LARKIN,  late  Conductor  of  the 
Brass  Foundry  Department  in  Reany,  Neafie  &  Co.'s  Penn 
Works,  Philadelphia.  New  edition,  revised,  with  extensive 
additions.  414  pages.  12mo .$2.50 

LEHNER. — The  Manufacture  of  Ink: 

Comprising  the  Raw  Materials,  and  the  Preparation  of 
Writing,  Copying  and  Hektograph  Inks,  Safety  Inks,  Ink 
Extracts  and  Powders,  etc.  Translated  from  the  German 
of  SIGMUND  LEHNER,  with  additions  by  WILLIAM  T.  BRANNT. 
Illustrated.  12mo $2.00 

LEROUX.— A  Practical  Treatise  on  the  Manufacture  of 
Worsteds  and  Carded  Yarns: 

Comprising  Practical  Mechanics,  with  Rules  and  Calcula- 
tions applied  to  Spinning;  Sorting,  Cleaning,  and  Scouring 
Wools;  the  English  and  French  Methods  of  Combing,  Draw- 
ing, and  Spinning  Worsteds,  and  Manufacturing  Carded 
Yarns.  Translated  from  the  French  of  CHARLES  LEROUX, 
Mechanical  Engineer  and  Superintendent  of  a  Spinning-Mill, 
by  HORATIO  PAINE,  M.  D.,  and  A.  A.  FESQUET,  Chemist  and 
Engineer.  Illustrated  by  twelve  large  Plates.  8vo $3.00 

LESLIE. — Complete  Cookery: 

Directions  for  Cookery  in  its  Various  Branches.  By  Miss 
LESLIE.  Sixtieth  thousand.  Thoroughly  revised,  with  the 
additions  of  New  Receipts.  12mo $1.00 

LE  VAN. — The  Steam  Engine  and  the  Indicator: 

Their  Origin  and  Progressive  Development;  including  the 
Most  Recent  ExamQles  of  Steam  and  Gas  Motors,  together 


HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE      17 

with  the  Indicator,  its  Principles,  its  Utility,  and  its  Applica- 
tion. By  WILLIAM  BARNET  LE  VAN.  Illustrated  by  205 
Engravings,  chiefly  of  Indicator-Cards.  469  pp.  8vo.  $2.00 

LIEBER. — Assayer's  Guide: 

Or,  Practical  Directions  to  Assayers,  Miners,  and  Smelters, 
for  the  Tests  and  Assays,  by  Heat  and  by  Wet  Processes,  for 
the  .Ores  of  all  the  principal  Metals,  of  Gold  and  Silver  Coins 
and  alloys,  and  of  Coal,  etc.  By  OSCAR  M.  LIEBER.  Re- 
vised. 283  pp.  12mo $1.50 

Lockwood's  Dictionary  of  Terms : 

Used  in  the  Practice  of  Mechanical  Engineering,  embracing 
those  Current  in  the  Drawing  Office,  Pattern  Shop,  Foundry, 
Fitting,  Turning,  Smith's  and  Boiler  Shops,  etc.,  etc.,  com- 
prising upwards  of  Six  Thousand  Definitions.  Edited  by  a 
Foreman  Pattern  Maker,  author  of  "Pattern  Making."  417 
pp.  12mo $3.75 

LUKIN.— The  Lathe  and  Its  Uses: 

Or  Instruction  in  the  Art  of  Turning  Wood  and  Metal.  In- 
cluding a  Description  of  the  Most  Modern  Appliances  for  the 
Ornamentation  of  Plane  and  Curved  Surfaces,  an  Entirely 
Novel  Form  of  Lathe  for  Eccentric  and  Rose-Engine  Turn- 
ing. A  Lathe  and  Planing  Machine  Combined;  and  Other 
Valuable  Matter  Relating  to  the  Art.  Illustrated  by  462 
engravings.  Seventh  Edition.  315  pages  8vo $4.25 

MAUCHLINE.— The  Mine  Foreman's  Hand-Book: 

Of  Practical  and  Theoretical  Information  on  the  Opening, 
Ventilating,  and  Working  of  Collieries.  Questions  and  An- 
swers on  Practical  and  Theoretical  Coal  Mining.  Designed 
to  Assist  Students  and  Others  in  Passing  Examinations  for 
Mine  Foremanships.  By  ROBERT  MAUCHLINE.  ,  3d  Edition. 
Thoroughly  Revised  and  Enlarged  by  F.  ERNEST  BRACKETT. 
134  Engravings.  8vo.  378  pages.  (1905.) $3.75 

MOLESWORTH.— Pocket-Book  of  Useful  Formulas  and 
Memoranda  for  Civil  and  Mechanical  Engineers: 

By  GUILFORD  L.  MOLESWORTH,  Member  of  the  Institution  of 
Civil  Engineers,  Chief  Resident  Engineer  of  the  Ceylon 
Railway.  Full-bound  in  Pocketbook  form $1.00 

MOORE.— The    Universal   Assistant   and    the    Complete 
Mechanic: 

Containing  over  one  million  Industrial  Facts,  Calculations, 
Receipts,  Processes,  Trades  Secrets,  Rules,  Business  Forms, 
Legal  Items,  etc.,  in  every  occupation,  from  the  Household 
to  the  Manufactory.  By  R.  MOORE.  Illustrated  by  500 
Engravings.  12mo $2.50 


18      HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE 

NAPIER. — A  System  of  Chemistry  Applied  to  Dyeing: 

By  JAMES  NAPIER,  F.  C.  S.  A  New  and  Thoroughly  Revised 
Edition.  Completely  brought  up  to  the  present  state  of  the 
Science,  including  the  Chemistry  of  Coal  Tar  Colors,  by  A. 
A.  FESQUET,  Chemist  and  Engineer.  With  an  Appendix  on 
Dyeing  and  Calico  Printing,  as  shown  at  the  Universal  Ex- 
position, Paris,  1867.  Illustrated.  8vo.  422  pages. .  .$2.00 

NICHOLLS.— The  Theoretical  and  Practical  Boiler-Maker 
and  Engineer's  Reference  Book: 

Containing  a  variety  of  Useful  Information  for  Employers 
of  Labor,  Foremen  and  Working  Boiler-Makers,  Iron,  Copper, 
and  Tinsmiths,  Draughtsmen,  Engineers,  the  General  Steam- 
using  Public,  and  for  the  Use  of  Science  Schools  and  classes 
By  SAMUEL  NICHOLLS.  Illustrated  by  sixteen  plates.  12mo. 

$2.50 

NYSTROM.— On  Technological  Education  and  the  Con- 
struction of  Ships  and  Screw  Propellers 
For  Naval  and  Marine  Engineers.  By  JOHN  W.  NYSTROM, 
late  Acting  Chief  Engineer,  U.  S.  N.  Second  Edition,  Re- 
vised, with  additional  matter.  Illustrated  by  seven  En- 
gravings. 12mo $1.00 

O'NEILL.— A  Dictionary  of  Dyeing  and  Calico  Printing: 

Containing  a  brief  account  of  all  the  Substances  and  Pro- 
cesses in  use  in  the  Art  of  Dyeing  and  Printing  Textile  Fabrics; 
with  Practical  Receipts  and  Scientific  Information.  By 
CHARLES  O'NEILL,  Analytical  Chemist.  To  which  is  added 
an  Essay  on  Coal  Tar  Colors  and  their  application  to  Dyeing 
and  Calico  Printing.  By  A.  A.  FESQUET,  Chemist  and  En- 
gineer. With  an  appendix  on  Dyeing  and  Calico  Printing, 
as  shown  at  the  Universal  Exposition,  Paris,  1867.  8vo. 
491  pages $2.00 

ORTON.— Underground  Treasures: 

How  and  Where  to  Find  Them.  A  Key  for  the  Ready  De- 
termination of  all  the  Useful  Minerals  within  the  United 
States.  By  JAMES  ORTON,  A.  M.,  Late  Professor  of  Natural 
History  in  Vassar  College,  N.  Y.;  author  of  the  "Andes  and 
the  Amazon,"  etc.  A  New  Edition,  with  An  Appendix  on 
Ore  Deposits  and  Testing  Minerals.  (1901.)  Illustrated. 

$1.50 

OSBORN. — A  Practical  Manual  of  Minerals,  Mines  and 
Mining: 

Comprising  the  Physical  Properties,  Geologic  Position;  Local 
Occurrence  and  Associations  of  the  Useful  Minerals,  their 
Methods  of  Chemical  Analysis  and  Assay;  together  with 
Various  Systems  of  Excavating  and  Timbering,  Brick  and 


HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE      19 

Masonry  Work,  during  Driving,  Lining,  Bracing  and  other 
Operations,  etc.  By  PROF.  H.  S.  OSBORN,  LL.  D.,  Author  of 
"The  Prospector's  Field-Book  and  Guide. "  171  Engravings. 
Second  Edition,  Revised.  8vo $4.50 

OSB3RN. — The  Prospector's  Field  Book  and  Guide: 

In  the  Search  For  and  the  Easy  Determination  of  Ores  and 
Other  Useful  Minerals.  By  PROF.  H.  S.  OSBORN,  LL.  D. 
Illustrated  by  66  Engravings.  Eighth  Edition.  Revised 
and  Enlarged.  401  pages.  12mo  (1910.) .$1.50 

OVERMAN. — The  Moulder's  and  Founder's  Pocket  Guide: 

A  Treatise  on  Moulding  and  Founding  in  Green-sand,  Dry- 
sand,  Loam,  and  Cement;  the  Moulding  of  Machine  Frames, 
Mill-gear,  Hollow  Ware,  Ornaments,  Trinkets,  Bells,  and 
Statues;  Description  of  Moulds  for  Iron,  Bronze,  Brass,  and 
other  Metals;  Plaster  of  Paris,  Sulphur,  Wax,  etc.;  the  Con- 
struction of  Melting  Furnaces,  the  Melting  and  Founding  of 
Metals;  the  Composition  of  Alloys  and  their  Nature,  etc., 
etc  By  FREDERICK  OVERMAN,  M.  E.  A  new  Edition,  to 
which  is  added  a  Supplement  on  Statuary  and  Ornamental 
Moulding,  Ordnance,  Malleable  Iron  Castings,  etc.  By  A. 
A.  FESQUET.  Chemist  and  Engineer.  Illustrated  by  44 
engravings.  12mo .$2.00 

PAINTER,  GILDER,  AND  VARNISHER'S  COMPANION: 

Comprising  the  Manufacture  and  Test  of  Pigments,  the  Arts 
of  Painting,  Graining,  Marbling,  Staining,  Sign-writing, 
Varnishing,  Glass-staining,  and  Gilding  on  Glass;  together 
with  Coach  Painting  and  Varnishing,  and  the  Principles  of 
the  Harmony  and  Contrast  of  Colors.  Twenty-seventh 
Edition.  Revised,  Enlarged,  and  in  great  part  Rewritten. 
By  WILLIAM  T.  BRANNT,  Editor  of  "Varnishes,  Lacquers, 
Printing  Inks  and  Sealing  Waxes."  Illustrated.  395  pp. 
12mo $1.50 

PERCY.— The  Manufacturing  of  Russian  Sheet- Iron: 
By  JOHN  PERCY,  M.  D.,  F.  R.  S.    Paper 25 

POSSELT.— Cotton  Manufacturing: 

Part  I.  Dealing  with  the  Fibre,  Ginning,  Mixing,  Picking, 
Scutching  and  Carding.  By  E.  A.  POSSELT.  104  Illustra- 
tions, 190  pp .- $3.00 

Part  II.    Combing,  Drawing,  Roller  Covering  and  Fly  Frame, 

$3.00 

POSSELT.— The   Jacquard   Machine   Analysed   and   Ex- 
plained : 

With  an  Appendix  on  the  Preparation  of  Jacquard  Cards,  and 
Practical  Hints  to  Learners  of  Jacquard  Designing.  By  E. 
A.  POSSELT.  With  230  Illustrations  and  numerous  diagrams. 
127  pp.  4to $3.00 


20     HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE 

POSSELT. — Recent  Improvements  in  Textile  Machinery 
Relating  to  Weaving: 

Giving  the  Most  Modern  Points  on  the  Construction  of  all 
Kinds  of  Looms,  Warpers,  Reamers,  Slashers,  Winders, 
Spoolers,  Reeds,  Temples,  Shuttles,  Bobbins,  Heddles,  Heddle 
Frames,  Pickers,  Jacquards,  Card  Stampers,  Etc.,  Etc.  By 
E.  A.  POSSELT.  4to.  Part  I,  600  ills.;  Part  II,  600  ills. 
Each  part $1.50 

POSSELT. — Recent  Improvements  in  Textile  Machinery, 
Part  III: 

Processes  Required  for  Converting  Wool,  Cotton,  Silk,  from 
Fibre  to  Finished  Fabric,  Covering  both  Woven  and  Knit 
Goods;  Construction  of  the  most  Modern  Improvements  in 
Preparatory  Machinery,  Carding,  Combing,  Drawing,  and 
Spinning  Machinery,  Winding,  Warping,  Slashing  Machinery, 
Looms,  Machinery  for  Knit  Goods,  Dye  Stuffs,  Chemicals, 
Soaps,  Latest  Improved  Accessories  Relating  to  Construc- 
tion and  Equipment  of  Modern  Textile  Manufacturing  Plants 
By  E.  A.  POSSELT.  Completely  Illustrated.  4to .....  $5.00 

POSSELT.— Technology  of  Textile  Design: 

The  Most  Complete  Treatise  on  the  Construction  and  Appli- 
cation of  Weaves  for  all  Textile  Fabrics  and  the  Analysis  of 
Cloth.  By  E.  A.  POSSELT.  1,500  Illustrations.  4to.  .$5.00 

POSSELT.— Textile  Calculations: 

A  Guide  to  Calculations  Relating  to  the  Manufacture  of  all 
Kinds  of  Yarns  and  Fabrics,  the  Analysis  of  Cloth,  Speed, 
Power  and  Belt  Calculations,  By  E.  A.  POSSELT.  Illus- 
trated. 4to $2.00 

REGNAULT. — Elements  of  Chemistry: 
By  M.  V.  REGNAULT.  Translated  from  the  French  by  T. 
FORREST  BETTON,  M.  D.,  and  edited,  with  Notes,  by  JAMES 
C.  BOOTH,  Melter  and  Refiner  U.  S.  Mint,  and  WILLIAM  L. 
FABER,  Metallurgist  and  Mining  Engineer.  Illustrated  by 
nearly  700  wood-engravings  Comprising  nearly  1,500  pages. 
In  two  volumes,  8vo.,  cloth $5.00 

RICH.— Artistic  Horse-Shoeing: 

A  Practical  and  Scientific  Treatise,  giving  Improved  Methods 
of  Shoeing,  with  Special  Directions  for  Shaping  Shoes  to  Cure 
Different  Diseases  of  the  Foot,  and  the  Correction  of  Faulty 
Action  in  Trotters.  By  GEORGE  E.  RICH.  362  Illustrations. 
217  pages.  12mo $2.00 

RICHARDSON.— Practical  Blacksmithing : 

A  Collection  of  Articles  Contributed  at  Different  Times  by 
Skilled  Workmen  to  the  columns  of  "The  Blacksmith  and 
Wheelwright,"  and  Covering  nearly  the  Whole  Range  ot 
Blacksmithing,  from  the  Simplest  Job  of  Work  to  some  of  the 


HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE     21 

most  Complex  Forgings  Compiled  and  Edited  by  M.  T. 
RICHARDSON. 

Vol.     I.     210  Illustrations.       224  pages.     12mo $1.00 

Vol.     II.     230  Illustrations.     262  pages.     12mo $1.00 

Vol.    III.    390  Illustrations.    307  pages.     12mo $1.00 

Vol.    IV.    226  Illustrations.    276  pages.     12mo $1.00 

RICHARDSON.— Practical  Carriage  Building: 
Comprising  Numerous  Short  Practical  Articles  upon  Carriage 
and  Wagon  Woodwork;  Plans  for  Factories;  Shop  and  Bench 
Tools;  Convenient  Appliances  for  Repair  Work;  Methods  of 
Working;  Peculiarities  of  Bent  Timber;  Construction  of 
Carriage  Parts;  Repairing  Wheels;  Forms  of  Tenons  and  Mor- 
tises; Together  with  a  Variety  of  Useful  Hints  and  Sugges- 
tions to  Woodworkers.  Compiled  by  M.  T.  RICHARDSON. 

Vol.  I.  228  Illustrations.  222  pages $1.00 

Vol.    II.    283  Illustrations.    280  pages $1.00 

RICHARDSON.— The  Practical  Horseshoer: 
Being  a  Collection  of  Articles  on  Horseshoeing  in  all  its 
Branches  which  have  appeared  from  time  to  time  in  the  col- 
umns of  "The  Blacksmith  and  Wheelwright,"  etc.    Compiled 
and  edited  by  M.  T.  RICHARDSON.     174  Illustrations,  $1.00 

RIFFAULT,  VERGNAUD,  and  TOUSSAINT.— A  Practical 
Treatise  on  the  Manufacture  of  Colors  for  Painting: 
Comprising  the  Origin,  Definition,  and  Classification  of  Colors, 
the  Treatment  of  the  Raw  Materials;  the  best  Formulae  and 
the  Newest  Processes  for  the  Preparation  of  every  description 
of  Pigment,  and  the  Necessary  Apparatus  and  Directions  for 
its  use;  Dryers;  the  Testing,  Application,  and  Qualities  of 
Paints,  etc.,  etc.  By  MM.  RIFFAULT,  VERGNAUD,  and 
TOUSSAINT,  Revised  and  Edited  by  M.  F.  MALPEYRE,  Trans- 
lated from  the  French  by  A.  A.  FESQUET.  Illustrated  by 
Eighty  Engravings.  659  pp.  8vo $5.00 

ROPER.— Catechism    for    Steam    Engineers    and    Elec- 
tricians : 

Including  the  Construction  and  Management  of  Steam  En- 
gines, Steam  Boilers  and  Electric  Plants.  By  STEPHEN 
ROPER  Twenty-first  edition,  rewritten  and  greatly  enlarged 
by  E.  R.  KELLER  and  C.  W.  PIKE.  365  pages.  Illustrations. 
18mo.,  tucks,  gilt $2.00 

ROPER.— Engineer's  Handy  Book: 
Containing  Facts,  Formulae,  Tables  and  Questions  on  Power, 
its  Generation,  Transmission  and  Measurement;  Heat,  Fuel, 
and  Steam;  The  Steam  Boiler  and  Accessories;  Steam  Engines 
and  their  Parts;  Steam  Engine  Indicator;  Gas  and  Gasoline 
Engines;  Materials;  their  Properties  and  Strength;  Together 
with  a  Discussion  of  the  Fundamental  Experiments  in  Elec- 
tricity, and  an  Explanation  of  Dynamos,  Motors,  Batteries, 
etc..  and  Rules  for  Calculating  Sizes  of  Wires.  By  STEPHEN 


22     HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE 

ROPER  15th  edition.  Revised  and  Enlarged  by  E.  R. 
KELLER,  M.  E.,  and  C.  W.  PIKE,  B.  S.  With  numerous 
Illustrations.  Pocket-book  form.  Leather $3.50 

ROPER. — Hand-Book  of  Land  and  Marine  Engines: 
Including  the  Modeling,  Construction,  Running,  and  Man- 
agement of  Land  and  Marine  Engines  and  Boilers.     With 
Illustrations.    By  STEPHEN  ROPER,  Engineer.    Sixth  Edition. 
12mo.,  tucks,  gilt  edge $3.50 

ROPER. — Hand-Book  of  the  Locomotive: 

Including  the  Construction  of  Engines  and  Boilers,  and  the 
Construction,  Management,  and  Running  of  Locomotives. 
By  STEPHEN  ROPER.  Eleventh  Edition.  18mo.,  tucks,  gilt 
edge $2.50 

ROPER. — Hand-Book  of  Modern  Steam  Fire-Engines; 
With  Illustrations.  By  STEPHEN  ROPER,  Engineer.  Fourth 
Edition,  12mo.,  tucks,  gilt  edge $3.50 

ROPER. — Instructions  and  Suggestions  for  Engineers  and 

Firemen : 
By  STEPHEN  ROPER,  Engineer.     18mo.,  Morocco $2.00 

ROPER. — Questions    and    Answers    for    Stationary    and 

Marine  Engineers  and  Electricians: 
With  a  Chapter  of  What  to  Do  in  Case  of  Accidents.  By 
STEPHEN  ROPER,  Engineer.  Sixth  Edition,  Rewritten  and 
Greatly  Enlarged  by  EDWIN  R.  KELLER,  M.  E.,  and  CLAYTON 
W.  PIKE,  B.  A.  306  pp.  Morocco,  pocketbook  form,  gilt 
edges $2.00 

ROPER. — The  Steam  Boiler:  Its  Care  and  Management: 
By  STEPHEN  ROPER,  Engineer.  12mo.,  tuck,  gilt  edges.  $2.00 

ROPER. — Use  and  Abuse  of  the  Steam  Boiler: 
By  STEPHEN  ROPER,  Engineer.    Ninth  Edition,  with  Illus- 
trations.    18mo.,  tucks,  gilt  edge $2.00 

ROPER — The  Young  Engineer's  Own  Book: 

Containing  an  Explanation  of  the  Principle  and  Theories  on 
which  the  Steam  Engine  as  a  Prime  Mover  is  based.  By 
STEPHEN  ROPER,  Engineer.  160  Illustrations,  363  pages. 
18mo.,  tuck $2.50 

ROSE. — The  Complete  Practical  Machinist: 

Embracing  Lathe  Work,  Vise  Work,  Drills  and  Drilling,  Taps 
and  Dies,  Hardening  and  Tempering,  the  Making  and  Use  of 
Tools,  Tool  Grinding,  Marking  out  work,  Machine  Tools,  etc. 
By  JOSHUA  ROSE.  395  Engravings.  Nineteenth  Edition, 
greatly  Enlarged  with  New  and  Valuable  Matter.  12mo., 
504  .pages $2.50 

ROSE. — Mechanical  Drawing  Self -Taught: 

Comprising  Instructions  in  the  Selection  and  Preparation  of 
Drawing  Instruments,  Elementary  Instruction  in  practical 


HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE      23 

Mechanical  Drawing,  together  with  Examples  in  Simple 
Geometry  and  Elementary  Mechanism,  including  Screw 
Threads,  Gear  Wheels,  Mechanical  Motions,  Engines  and 
Boilers.  By  JOSHUA  ROSE,  M.  E.  Illustrated  by  330  En- 
gravings. 8vo.  313  pages $3.50 

ROSE. — The  Slide- Valve  Practically  Explained: 

Embracing  simple  and  complete  Practical  Demonstrations  of 
the  operation  of  each  element  in  a  Slide-valve  Movement, 
and  illustrating  the  effects  of  Variations  in  their  Proportions 
by  examples  carefully  selected  from  the  most  recent  and 
successful  practice.  By  JOSHUA  ROSE,  M.  E.  Illustrated 
by  35  Engravings $1.00 

ROSE. — Steam  Boilers: 

A  Practical  Treatise  on  Boiler  Construction  and  Examination, 
for  the  Use  of  Practical  Boiler  Makers,  Boiler  Users,  and  In- 
spectors; and  embracing  in  plain  figures  all  the  calculations 
necessary  in  Designing  or  Classifying  Steam  Boilers.  By 
JOSHUA  ROSE,  M.  E.  Illustrated  by  73  Engravings.  250 
pages.  8vo $2.00 

ROSS. — The    Blowpipe    in    Chemistry,    Mineralogy    and 
Geology : 

Containing  all  Known  Methods  of  Anhydrous  Analysis,  many 
Working  Examples,  and  Instructions  for  Making  Apparatus. 
By  LIEUT  COLONEL  W  A.  Ross,  R.  A..  F.  G.  S.  With  120 
Illustrations.  12mo $2.00 

SCHRIBER.— The  Complete  Carriage  and  Wagon  Painter: 

A  Concise  Compendium  of 'the  Art  of  Painting  Carriages, 
Wagons,  and  Sleighs,  embracing  Full  Directions  in  all  the 
Various  Branches,  including  Lettering,  Scrolling,  Ornament- 
ing, Striping,  Varnishing,  and  Coloring,  with  numerous  Re- 
cipes for  Mixing  Colors.  73  Illustrations.  177  pp.  12mo. 

$1.00 

SHAW.— Civil  Architecture: 

Being  a  Complete  Theoretical  and  Practical  System  of  Build- 
ing, containing  the  Fundamental  Principles  of  the  Art.  By 
EDWARD  SHAW,  Architect.  To  which  is  added  a  Treatise  on 
Gothic  Architecture,  etc.  By  THOMAS  W.  SILLOWAY  and 
GEORGE  M.  HARDING,  Architects.  The  whole  illustrated  by 
102  quarto  plates  finely  engraved  on  copper.  Eleventh  Edi- 
tion 4to ." .  .$5.00 

SHERRATT.— The  Elements  of  Hand-Railing: 

Simplified  and  Explained  in  Concise  Problems  that  are  Easily 
Understood.  The  whole  illustrated  with  Thirty-eight  Ac- 
curate and  Original  Plates,  Founded  on  Geometrical  Principles, 
and  showing  how  to  Make  Rail  Without  Centre  Joints,  Mak- 
ing Better  Rail  of  the  Same  Material,  with  Half  the  Labor, 


24      HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE 

and  Showing  How  to  Lay  Out  Stairs  of  all  Kinds.  By  R.  J. 
SHERRATT.  Folio $2.50 

SHUNK. — A  Practical  Treatise  on  Railway  Curves  and 
Location  for  Young  Engineers: 

By  W.  F.  SHUNK,  C.  E.  12mo.  Full  bound  pocket-book 
form $2.00 

SLOANE. — Home  Experiments  in  Science: 
By  T.  O'CoNOR  SLOANE,  E.  M..  A  M.,  Ph.  D.    Illustrated 
by  91  Engravings.     12mo $1.00 

SLOAN. — Homestead  Architecture : 
Containing  Forty  Designs  for  Villas,  Cottages,  and  Farm- 
houses, with  Essays  on  Style,  Construction,  Landscape  Gar- 
dening, Furniture,  etc.,  etc.     Illustrated  by  upwards  of  200 
Engravings.    By  SAMUEL  SLOAN,  Architect.    8vo $2.00 

SMITH. — The  Dyer's  Instructor: 

Comprising  Practical  Instructions  in  the  Art  of  Dyeing  Silk, 
Cotton,  Wool,  and  Worsted,  and  Woolen  Goods;  containing 
nearly  800  Receipts.  To  which  is  added  a  Treatise  on  the 
Art  of  Padding;  and  the  Printing  of  Silk  Warps,  Skeins,  and 
Handkerchiefs,  and  the  various  Mordants  and  Colors  for  the 
different  styles  of  such  work.  By  DAVID  SMITH,  Pattern 
Dyer.  12mo $1.00 

SMITH. — A  Manual  of  Political  Economy: 
By  E.  PESHINE  SMITH.    A  New  Edition,  to  which  is  added 
a  full  Index.     12mo $1.25 

SMITH. — Parks  and  Pleasure- Grounds: 
Or  Practical  Notes  on  Country  Residences,  Villas,  Public 
Parks,  and  Gardens.    By  CHARLES  H.  J.  SMITH,  Landscape 
Gardener  and  Garden  Architect,  etc.,  etc.     12mo $2.00 

SNIVELY.— The    Elements     of     Systematic     Qualitative 

Chemical  Analysis: 

A  Hand-book  for  Beginners.  By  JOHN  H.  SNIVELY,  Phr.  D. 
16mo $2.00 

STOKES.— The  Cabinet  Maker  and  Upholsterer's  Com- 
panion : 

Comprising  the  Art  of  Drawing,  as  applicable  to  Cabinet 
Work;  Veneering,  Inlaying,  and  Buhl- Work;  the  Art  of  Dye- 
ing and  Staining  Wood,  Ivory,  Bone,  Tortoise-Shell,  etc. 
Directions  for  Lacquering,  Japanning,  and  Varnishing;  to 
make  French  Polish,  Glues,  Cements,  and  Compositions; 
with  numerous  Receipts,  useful  to  workmen  generally.  By 
J.  STOKES.  Illustrated.  A  New  Edition,  with  an  Appendix 
upon  French  Polishing,  Staining,  Imitating,  Varnishing,  etc., 
etc.  12mo $1.25 

STRENGTH   AND   OTHER   PROPERTIES   OB    METALS: 
Reports  of  Experiments  on  the  Strength  and  other  Properties 


HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE      25 

of  Metals  for  Cannon  With  a  Description  of  the  Machines 
for  Testing  Metals,  and  of  the  Classification  of  Cannon  in 
service.  By  Officers  of  the  Ordnance  Department,  U.  S. 
Army.  By  authority  of  the  Secretary  of  War.  Illustrated 
by  25  large  steel  plates.  Quarto $3.00 

SULZ. — A  Treatise  on  Beverages: 

Or  the  Complete  Practical  Bottler.  Full  Instructions  for 
Laboratory  Work  with  Original  Practical  Recipes  for  all 
kinds  of  Carbonated  Drinks,  Mineral  Waters,  Flavoring 
Extracts,  Syrups,  etc.  By  CHARLES  HERMAN  SULZ,  Tech- 
nical Chemist  and  Practical  Bottler.  Illustrated  by  428 

Engravings.     818  pp.     8vo $7.50 

SYME.— Outlines  of  an  Industrial  Science: 
By  DAVID  SYME.    12mo $2.00 

TABLES  SHOWING  THE  WEIGHT  OF  ROUND,  SQUARE 
AND  FLAT  BAR  IRON,  STEEL,  ETC. 

By  Measurement.    Cloth 63 

TEMPLETON. — The  Practical  Examinator  on  Steam  and 
the  Steam-Engine: 

With  Instructive  References  relative  thereto,  arranged  for 
the  Use  of  Engineers,  Students,  and  others.  By  WILLIAM 

TEMPLETON,  Engineer     12mo $1.00 

THALLNER.— Tool-Steel: 

A  Concise  Hand-book  on  Tool-Steel  in  General.  Its  Treat- 
ment in  the  Operations  of  Forging,  Annealing,  Hardening, 
Tempering,  etc.,  and  the  Appliances  Therefor.  By  OTTO 
THALLNER,  Manager  in  Chief  of  the  Tool-Steel  Works,  Bis- 
marckhutte,  Germany.  From  the  German  by  WILLIAM  T. 
BRANNT.  Illustrated  by  69  Engravings.  194  pages  8vo. 
1902 $2.00 

THAUSING.— The  Theory  and  Practice  of  the  Preparation 
of  Malt  and  the  Fabrication  of  Beer: 

With  especial  reference  to  the  Vienna  Process  of  Brewing. 
Elaborated  from  personal  experience  by  JULIUS  E.  THAUSING, 
Professor  at  the  School  for  Brewers,  and  at  the  Agricultural 
Institute,  Modling,  near  Vienna.  Translated  from  the  Ger- 
man by  WILLIAM  T.  BRANNT.  Thoroughly  and  elaborately 
edited,  with  much  American  matter,  and  according  to  the 
latest  and  most  Scientific  Practice,  by  A.  SCHWARZ  and  DR. 
A.  H.  BAUER  Illustrated  by  140  Engravings.  8vo.  815 

pages $10.0 

TOMPKINS.— Cotton  and  Cotton  Oil: 
Cotton:    Planting,  Cultivating,  Harvesting  and  Preparation 
for  Market.    Cotton  Seed  Oil  Mills:    Organization,  Construc- 
tion and  Operation.    Cattle  Feeding:    Production  of  Beef 
and  Dairy  Products,  Cotton  Seed  Meal  and  Hulls  as  Stock 


26     HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE 

Feed.  Fertilizers:  Manufacture,  Manipulation  and  Uses. 
By  D.  A.  TOMPKINS.  8vo.  494pp.  Illustrated $7.50 

TOMPKINS.— Cotton  Mill,  Commercial  Features: 

A  Text-Book  for  the  Use  of  Textile  Schools  and  Investors. 
With  Tables  showing  Cost  of  Machinery  and  Equipments 
for  Mills  making  Cotton  Yarns  and  Plain  Cotton  Cloths.  By 
D.  A.  TOMPKINS.  8vo.  240  pp.  Illustrated .$5.00 

TOMPKINS. — Cotton  Mill  Processes  and  Calculations: 

An  Elementary  Text-Book  for  the  Use  of  Textile  Schools  and 
for  Home  Study.  By  D.  A  TOMPKINS.  312  pp.  8vo. 
Illustrated $5.00 

TURNER'S  (THE)  COMPANION: 

Containing  Instructions  in  Concentric,  Elliptic,  and  Eccen- 
tric Turning;  also  various  Plates  of  Chucks,  Tools,  and  In- 
struments; and  Directions  for  using  the  Eccentric  Cutter, 
Drill,  Vertical  Cutter,  and  Circular  Rest;  with  Patterns  and 
Instructions  for  working  them.  12mo $1.00 

VAN  CLEVE.— The  English  and  American  Mechanic: 
Comprising  a  Collection  of  Over  Three  Thousand  Receipts, 
Rules,  and  Tables,  designed  for  the  Use  of  every  Mechanic 
and  Manufacturer.    By  B.  FRANK  VAN  CLEVE.    Illustrated. 
500  pp.     12mo $2.00 

VAN  DER  BURG.— School  of  Painting  for  the  Imitation 

of  Woods  and  Marbles: 

A  Complete,  Practical  Treatise  on  the  Art  and  Craft  of  Grain- 
ing and  Marbling  with  the  Tools  and  Appliances.  36  Plates. 
Folio,  12x20  inches $6.00 

VILLE. — The  School  of  Chemical  Manures: 
Or,  Elementary  Principles  in  the  Use  of  Fertilizing  Agents 
From  the  French  of  M.  GEO.  VILLE,  by  A.  A.  FESQUET, 
Chemist  and  Engineer.     With  Illustrations.     12mo $1.25 

VOGDES. — The   Architect's   and   Builder's   Pocket-Com- 
panion and  Price-Book: 

Consisting  of  a  Short  but  Comprehensive  Epitome  of  Deci- 
mals, Duodecimals,  Geometry  and  Mensuration;  with  Tables 
of  United  States  Measures,  Sizes,  Weights,  Strength,  etc,,  of 

'  Iron,  Wood,  Stone,  Brick,  Cement  and  Concretes,  Quanti- 
ties of  Materials  in  given  Sizes  and  Dimensions  of  Wood, 
Brick  and  Stone;  and  full  and  complete  Bills  of  Prices  for 
Carpenter's  Work  and  Painting;  also,  Rules  for  Computing 
and  Valuing  Brick  and  Brick  Work,  Stone  Work,  Painting, 
Plastering,  with  a  Vocabulary  of  Technical  Terms,  etc.  By 
FRANK  W.  VOGDES,  Architect,  Indianapolis,  Ind.  Enlarged, 
Revised  and  Corrected.  In  one  volume  368  pages,  full- 
bound,  pocketbook  form,  gilt  edges $2.00 

Cloth..  ..$150 


HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE      27 

WAHNSGHAFFE.— A  Guide  to  the  Scientific  Examina- 
tion of  Soils: 

Comprising  Select  Methods  of  Mechanical  and  Chemical 
Analysis  and  Physical  Investigation.  Translated  from  the 
German  of  DR  F.  WAHNSCHAFFE.  With  additions  by  WIL- 
LIAM T.  BRANNT.  Illustrated  by  25  Engravings.  12mo. 
177  pages $1.50 

WARE.— The  Sugar  Beet: 

Including  a  History  of  the  Beet  Sugar  Industry  in  Europe, 
Varieties  of  the  Sugar  Beet,  Examinatioi,  Soils,  Tillage 
Seeds  and  Sowing,  Yield  and  Cost  of  Cultivation,  Harvest- 
ing, Transportation,  Conservation,  Feeding  Qualities  of  the 
Beet  and  of  the  Pulp,  etc.  By  LEWIS  S.  WARE,  C.  E., 
M.  E.  Illustrated  by  ninety  Engravings.  8vo .$2.00 

WARN. — The  Sheet-Metal  Worker's  Instructor: 
For  Zinc,  Sheet-Iron,  Copper,  and  Tin-Plate  Workers,  etc. 
Containing  a  selection  of  Geometrical  Problems;  als:>  Prac- 
tical and  Simple  Rules  for  Describing  the  various  Patterns 
required  in  the  different  branches  of  the  above  Trades.  By 
REUBEN  H.  WARN,  Practical  Tin-Plate  Worker.  To  which  is 
added  an  Appendix,  containing  Instructions  for  Boiler-Mak- 
ing, Mensuration  of  Surfaces  and  Solids,  Rules  for  Calculat- 
ing the  Weights  of  different  Figures  of  Iron  and  Steel,  Tables 
of  the  Weights  of  Iroi,  Steel,  etc.  Illustrated  by  thirty- 
two  Plates  and  thirty-seven  Wood  Engravings.  8vo. . .  $2.00 

WANNER. — New  Theorems,   Tables,   and   Diagrams,   for 

the  Computation  of  Earth- work: 

Designed  for  the  use  of  Engineers  in  Preliminary  and  Final 
Estimates,  of  Students  in  Engineering  and  of  Contra^rs 
and  other  non-professional  Computers.  In  two  parts,  with 
an  Appendix.  Part  I.  A  Practical  Treatise;  Part  II.  A 
Theoretical  Treatise,  and  the  Appendix  Contaiiing  Notes  to 
the  Rules  and  Examples  of  Part  I.;  Explanations  of  the  Con- 
struction of  Scales,  Tables,  and  Diagrams,  and  a  Treatise 
upon  Equivalent  Square  Bases  and  Equivalent  Level  Heights. 
By  JOHN  WARNER,  A.  M.,  Mining  and  Mechanical  Engineer. 
Illustrated  by  14  Plates.  8vo $3.00 

WATSON  —A  Manual  of  the  Hand-Lathe: 
Comprising  Concise  Directions  for  Working  Metals  of  all 
kinds,  Ivory,  Bone  and  Precious  Woods;  Dyeing,  Coloring, 
and  French  Polishing;  Inlaying  by  Veneers,  and  various 
methods  practised  to  produce  Elaborate  work  with  dispatch, 
and  at  Small  Expense.  By  EGBERT  P.  WATSON,  Author  of 
"The  Modern  Practice  of  American  Machinists  and  En- 
gineers." Illustrated  by  78  Engravings  ...  "51.00 

WATSON. — The  Modern  Practice  of  American  Machinists 

and  Engineers: 
Including  the  Construction,  Application,  and  Use  of  Drills, 


28      HENRY  CAREY  BAIRD  &  CO.'S  CATALOGUE 

Lathe  Tools,  Cutters  for  Boring  Cylinders,  and  Hollow-work 
generally,  with  the  most  economical  Speed  for  the  same;  the 
Results  verified  by  Actual  Practice  at  the  Lathe,  the  Vise, 
and  on  the  floor.  Together  with  Workshop  Management, 
Economy  of  Manufacture,  the  Steam  Engine,  Boilers,  Gears, 
Belting,  etc.,  etc.  By  EGBERT  P.  WATSON  Illustrated  by 
eighty-six  Engravings.  12mo $2.00 

WEATHERLY. — Treatise  on  the  Art  of  Boiling  Sugar, 
Crystallizing,  Lozenge-making,  Comfits,  Gum  Goods : 
And  other  processes  for  Confectionery,  including  Methods 
for  Manufacturing  every  Description  of  Raw  and  Refined 
Sugar  Goods.  A  New  and  Enlarged  Edition,  with  an  Appen- 
dix on  Cocoa,  Chocolate,  Chocolate  Confections,  etc.  196 
pages.  12mo $1.50 

WILL. — Tables  of  Qualitative  Chemical  Analysis: 
With  an  Introductory  Chapter  on  the  Course  of  Analysis 
By  PROFESSOR  HEINRICH  WILL,  of  Giessen,  Germany.  Third 
American,  from  the  eleventh  German  Edition.  Edited  by 
CHARLES  F.  HIMES,  Ph.  D  ,  Professor  of  Natural  Science 
Dickinson  College,  Carlisle,  Pa.  8vo $1.00 

WILLIAMS.— On  Heat  and  Steam: 
Embracing  New  Views  of  Vaporization,  Condensation  and 
Explosion.    By  CHARLES  WYE  WILLIAMS,  A.  I.  C.  E.    Illus- 
trated.   8vo $2.00 

WILSON. — The  Practical  Tool-Maker  and  Designer: 
A  Treatise  upon  the  Designing  of  Tools  and  Fixtures  for 
Machine  Tools  and  Metal  Working  Machinery,  Comprising 
Modern  Examples  of  Machines  with  Fundamental  Designs 
for  Tools  for  the  Actual  Production  of  the  work;  Together 
with  Special  Reference  to  a  Set  of  Tools  for  Machining  the 
Various  Parts  of  a  Bicycle.  Illustrated  by  189  Engravings 

(1898) $2.50 

CONTENTS  :  Introductory.  Chapter  I.  Modern  Tool  Room  and 
Equipment.  II.  Files,  Their  Use  and  Abuse.  III.  Steel  and  Tem- 
pering. IV.  Making  Jigs.  V.  Milling  Machine  Fixtures.  VI.  Tools 
and  Fixtures  for  Screw  Machines.  VII.  Broaching.  VIII.  Punches 
and  Dies  for  Cutting  and  Drop  Press.  IX.  Tools  for  Hollow-ware. 

X.  Embossing:   Metal,   Coin  and  Stamped  Sheet-Metal  Ornaments. 

XI.  Drop  Forging.     XII.  Solid  Drawn  Shells  or  Ferrules  ;  Cupping 
or  Cutting  and  Drawing ;  Breaking  Down  Shells.     XIII.  Annealing, 
Pickling  and  Cleaning.     XIV.  Tools  for  Draw  Bench.     XV.  Cutting 
and  Assembling  Pieces  by  Means  of   Ratchet  Dial   Plates   at  One 
Operation.     XVI.  The  Header.     XVII.  Tools  for  Fox  Lathe.    XVIII. 
Suggestions  for  a  set  of  Tools  for  Machining  the  Various  Parts  of 
a  Bicycle.     XIX.  The  Plater's  Dynamo.     XX.  Conclusion — With  a 
few  Random  Ideas.     Appendix.     Index. 

WORSSAM.— On  Mechanical  Saws: 

From  the  Transaction  of  the  Society  of  Engineers,  1869.  By 
S.  W.  WORSSAM,  JR.  Illustrated  by  Eighteen  large  Plates. 
8vo...  ...$1.50 


BRANNTS  "SOAP  MAKER'S  HAND  BOOK.1 


The  most  helpful  and  up-to-date  book  on  the  Art  of  Soap 
Making  in  the  English  language. 

In  one  volume,  8vo,  535  pages,  illustrated  by  54:  engravings. 
Price  $6.OO  net,  Free  of  Postage  to  any  Address  in  the  World, 
or  by  Express  C.  O.  D.  freight  paid  to  any  Address  in  the 
United  States  or  Canada. 


PUBLISHED   APRIL,  1912. 


THE 

SOAP  MAKER'S  HAND  BOOK 

OF 

MATERIALS,  PROCESSES  AND  RECEIPTS  FOR 
EVERY  DESCRIPTION  OF  SOAP 

INCLUDING 

FATS,  FAT  OILS,  AND  FATTY  ACIDS ;   EXAMINATION  OF  FATS  AND  OILS  ; 

ALKALIES  ;   TESTING  SODA  AND  POTASH  ;   MACHINES  AND  UTENSILS  J 

HARD  SOAPS  ;  SOFT  SOAPS  ;  TEXTILE  SOAPS  ;  WASHING  POWDERS 

AND  ALLIED  PRODUCTS  J    TOILET  SOAPS,  MEDICATED  SOAPS, 

AND  SOAP  SPECIALTIES  ;    ESSENTIAL  OILS  AND   OTHER 

PERFUMING   MATERIALS  ;    TESTING  SOAPS. 

EDITED   CHIEFLY   FROM   THE   GERMAN   OF 
DR.  C.  DEITE,     A.  ENGELHARDT,     F.  WILTNER, 

AND  NUMEROUS  OTHER  EXPERTS. 

WITH  ADDITIONS 
BY 

WILLIAM  T.  BRANNT, 

EDITOR  OF  "THE  TECHNO  CHEMICAL  RECEIPT  BOOK." 

ILLUSTRATED  BY  FIFTY-FOUR  ENGRAVINGS. 
SECOND  EDITION.  REVISED  AND  IN  GREAT  PART  RE-WRITTEN. 

PHILADELPHIA  : 
HENRY  CAREY  BAIRD  &  CO., 

INDUSTRIAL  PUBLISHEES,  BOOKSELLERS,  AND  IMPORTERS, 

810  WALNUT  STBEET. 

1912 


KIRK'S  CUPOLA   FURNACE.. 


An  Eminently,  Practical,  Up-to-Date  Book,  by  an  Expert. 

Third  Thoroughly  Revised  and  Partly  Re-written  Edition. 
In  one  volume,  8vo.9  482  pages,  illustrated  by  one  hundred 
and  sioc  engravings.  Price  $3.50.  Free  of  Postage  to  any 
Address  in  the  World,  or  by  Express  C,  O.  D.,  freight  paid  to 
any  Address  in  the  United  States  or  Canada. 


PUBLISHED  AUGUST,  1910. 


THE    CUPOLA    FURNACE 

A  PRACTICAL  TREATISE  ON  THE 

CONSTRUCTION  AND  MANAGEMENT 


OF 

FOUNDRY  CUPOLAS: 

COMPRISING 

IMPROVEMENTS   IN   CUPOLAS  AND  METHODS   OF  THEIR  CONSTRUCTION  AND   MANAGE- 
MENT; TUYERES;  MODERN  CUPOLAS;  CUPOLA  FUELS;  FLUXING  OF  IRON;  GETTING 

UP  CUPOLA   STOCK;    RUNNING  A  CONTINUOUS   STREAM;    SCIENTIFICALLY 

DESIGNED  CUPOLAS;  SPARK-CATCHING  DEVICES;  BLAST-PIPES  AND 
BLAST;  BLOWERS;  FOUNDRY  TRAM  RAIL,  ETC.,  ETC. 


BY 

EDWARD   KIRK, 

PRACTICAL  MOULDER  AND   MELTER,  CONSULTING   EXPERT  IN  MELTING. 

Author  of  "  The  Founding  of  Metals"  and  of  Numerous  Papers  on  Cupola  Practice* 

ILLUSTRATED  BY  ONE  HUNDRED  AND  SIX  ENGRAVINGS. 

THIRD  THOROUGHLY  REVISED  AND  PARTLY  RE-WR.TTEN   EDITION. 


PHILADELPHIA  : 
HENRY  CAREY  BAIRD  &  CO., 

INDUSTRIAL  PUBLISHERS,  BOOKSELLERS,  AND  IMPOETERS, 

810  WALNUT  STREET. 

1912 


KIRK'S    FOUNDRY   IRONS. 


A.  Practical,  Up-to-Date  Book,  by  the  well  known  Expert. 

In  one  volume,  8vo,  294:  pages,  illustrated.  Price  $3.OO  net. 
free  of  Postage  to  any  Address  in  the  World,  or  by  Express 
C.  O.  D.,  freight  paid  to  any  Address  in  the  United  States  or 
Canada.  * 


PUBLISHED  JUNE,   1911. 


A  PRACTICAL  TREATISE 

ON 

FOUNDRY   IRONS 

COMPRISING 

PIG    IRON,  AND   FRACTURE   GRADING   OF   PIG   AND   SCRAP   IRONS  ; 
SCRAP  IRONS  ;    MIXING  IRONS  ;    ELEMENTS  AND  METALLOIDS  ; 
GRADING   IRON   BY   ANALYSIS  ;    CHEMICAL   STANDARDS 
FOR  IRON  CASTINGS  ;   TESTING  CAST  IRON  ;    SEMI- 
STEEL  ;    MALLEABLE   IRON  ;    ETC.,  ETC. 


BY 

EDWARD   KIRK, 

PRACTICAL  MOULDER  AND  MELTER;  CONSULTING  EXPERT  IN  MELTING. 

AUTHOR  OF  "THK  CUPOLA  FURNACE,"  AND  OF  NUMEROUS 

PAPEKS  ON  CUPOLA  PRACTICE. 


ILLUSTRATED 


PHILADELPHIA : 
HENRY  CAREY  BAIRD  &  CO., 

INDUSTRIAL  PUBLISHERS,  BOOKSELLERS  AND  IMPORTERS, 

810  WALNUT  STREET. 

1911 


BRANNT'S  DRY  CLEANER. 


The  only  book  including  Hat  Cleaning  and  ^Reno- 
vating in  any  language,  in  one  volume,  12mo,  371 
pages,  illustrated.  Price  $2. SO  net.  Free  of  postage 
to  any  address  in  the  world,  or  by  express  freight 
paid  to  any  address  in  the  United  States  or  Canada. 

PUBLISHED  OCTOBER,  1911. 

THE  PRACTICAL 

DRY  CLEANER,  SCOURER,  AND 
GARMENT  DYER: 

COMPRISING 

DRY,  CHEMICAL,  OR  FRENCH  CLEANING;  PURIFICATION  OF  BENZINE; 

REMOVAL  OF  STAINS,  OR  SPOTTING;  WET  CLEANING;  FINISHING 

CLEANED  FABRICS;  CLEANING  AND  DYEING  FURS,  SKIN  RUGS 

AND  MATS;  CLEANING  AND  DYEING  FEATHERS;  CLEANING 

AND  RENOVATING  FELT,  STRAW  AND  PANAMA  HATS; 

BLEACHING  AND  DYEING  STRAW  AND  STRAW  HATS; 

CLEANING  AND  DVEING  GLOVES;  GARMENT 

DYEING;  STRIPPING;  ANALYSIS  OF 

TEXTILE  FABRICS. 

/ 

EDITED    BY 

WILLIAM  T.  BRANNT, 

EDITOR  OF  "THE  TECHNO-CHEMICAL  RECEIPT  BOOK." 

FOURTH  EDITION,  REVISED  AND  ENLARGED. 

ILLUSTRATED  BY  FORTY-ONE  ENGRAVINGS. 

PHILADELPHIA: 

HENRY  CAREY  BAIRD  &  CO, 

INDUSTRIAL   PUBLISHERS,    BOOKSELLERS    AKD   IMPORTERS, 

810  WALNUT  STREET. 
1911. 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
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